Needle shim modification

[clark911dispatcher]

The GZ in its stock form comes ridiculously lean from the factory in order to satisfy the EPA. Here is the modification that I, as well as Pat Henry, documented over on the Yahoo board. Hopefully it will be a help to those who want to fatten up the mix just a bit.


How to remedy the lean carb setting:


Original Post:

After reading a lot about shimming the needle on the carburetor to counteract the leanness of the bike, I decided to do just that this afternoon.

Went to the hardware store, bought the appropriate washer and headed back home to tear into my little project.

On the GZ, the carburetor sits directly beneath the frame and where it makes a "Y" to split down both sides of the bike. The two screws that hold the top on the carburetor are easy to get to but watch which Phillips screwdriver you use, as a #2 doesn't like that screw.

Once you have the screws almost removed, grab hold of the top of the carb. The reason for this is when you remove that top there is a spring, approximately 5-6 inches long that will come flying out of the carb. It takes a little finesse, but if you will hold the carb top with your left hand, and take two fingers and compress the spring down into the carb then you can remove the top between the forks of the "Y" that I spoke of earlier.

Removing the diaphragm is a delicate proposition. I sincerly think that body prophylactics are stronger than this particular diaphragm. :D Again, you can remove it between the forks of the "Y", just don't manhandle it. It is a VERY delicate membrane and will tear easily if handled wrong.

Once you have the diaphragm and the needle body pulled, there is a plastic "thing" -- for lack of a better term, that has a rubber washer on the end of it that holds the needle assembly in place. Be careful when you remove this (with needle nose pliers). It is not threaded, and simply pulls straight out. The caution comes because there is a tiny spring underneath that plastic piece, which allows the needle to move up and down. It can be lost VERY easily. Also, there is a tiny washer that sits on the very top of the needle beneath that spring I just spoke of. Again, easy to lose if you aren't expecting it.

Once that plastic piece is removed, you can then lift the needle out of the slide assembly. You will then slide the washer up the needle and against the plastic shim that is already provided stock on the needle. [please read the beginning notes for suggestions before continuing] Once you have done this reassemble carefully, taking care to make sure everything is free, with no binding, and that all parts are replaced in the order you removed them.

My result from this. I took a test ride afterwards, and the bike does seem more confident moving up through the rpm range. I occasionally would notice a bit of lag in spots during acceleration, and this seems to be gone. I'm going back out in a bit to ride it for several miles and should have an even better feel for this mod then.

It is a modification that is easy to undo if you decide you don't like the resulting effect.

Thought I'd share this with the group if anyone has been toying with the idea and wants to try it.

Tom


Here is Pat's addition to the needle shim modification...

After Tom's excellent description, I finally got the chance to go out and do this mod today. What a pleasant-to-ride bike this has become after the modification (not that it was bad before). But it now has a much more linear and even throttle response - at least under the cool/humid conditions that I rode under today! Very nice.

Some important notes in addition to Tom's excellent comments (which should be read carefully). Suzuki makes it really easy to do this modification on the GZ250: you don't really need to buy an additional washer! Just take the washer that's already there, the one directly above the needle circlip and underneath the spring, and move it to just below the circlip (where it will raise the needle slightly). The spring will seat directly on the circlip after the mod., which I figure is OK since there is no movement - the spring just keeps everything seated in place.

Some additional notes in addition to Tom's: It's probably best to put the washer directly underneath the circlip and above the longer plastic spacer that's alread there (remove the plastic spacer and place the washer above it), rather than below the plastic spacer. Reason? This long plastic spacer has a flat spot at the bottom on one side that must match the mating flat spot in the slide/diaphragm that it sets on in order to seat properly (I almost didn't see
this). If you insert the washer at the bottom of the plastic spacer, it could sit a little cock-eyed on this indentation causing an alignment problem.

All in all this is a simple mod. to do provided you take your time and are careful not to lose or damage anything. For those that believe a picture is worth a 1000 words: take 9 in this picture and put it between 10 and 11. You've done the mod!!

http://www.ronayers.com/fiche/300_0304/ ... arent=6620 (http://www.ronayers.com/fiche/300_0304/carburetor/carburetor.cfm?man=su&groupid=6680&parent=6620)
or
http://tinyurl.com/8s4qv

This Suzuki washer seems to be slightly thicker than an equivalent hardware store version. And it fits perfectly without modification.

Amazing, I've had this thing (GZ250) 5 years and am still learning!

Pat

[Dupo]

Good deal, was hoping one of you guys would post this. If you want, you can put a copy of this in the HowTo section as well.

[clark911dispatcher]

If you want to move it, feel free to. I guess I overlooked the How-To section! :D

[Rebel13]

That's all you have to do? Any noticable gain after doing this? Also, is there a way to get it even more richer?

[Dupo]

Yes, look in the how to section for my muffler swap. I have in there how to get the plug off the carb to gain access to the mixture screw.

[jokerbluffer]

Do you need to remove the tank to ba able to access carb better?

[Dupo]

Yes.

[Badbob]

I did this yesterday and the flat spots completely vanished. I used the move the washer method described above. It worked great. I removed the clip and moved the washer to the other side and reinstalled the clip. At some point I'm going to get a washer and put the stock washer back where it is supposed to be.

To do this I had to remove the gas tank, both side panels, air box bolts, and the carburetor. I tried getting the diaphragm out with out removing the carburetor but found this difficult. In my garage dropped parts vanish. I suggest removing the carburetor and doing the disassembly in the bottom of a clean white 5 gallon bucket so when the spring pops out it will be in the bucket. Working inside a clear plastic bag also works well.

I think my wifes bike has already had this done when we got it because it has no flat spots. It's still smoother and quieter than mine.

[Dupo]

Hmm, diaphragm came out pretty easy on mine. Putting it back on was a 'little' tricky but went ok. Its good knowing about the spring BEFORE you take it off, so i was careful lol.

[Badbob]

in the tight space when the cap didn't come right off I stopped and considered that there are springs in there I don't want to bend tiny little parts I don't want to loose. Safe is better than sorry in my book. Anyway I got to look in side my carburetor after 13,000 mile. Very clean. Shiny.

[Jordan310]

After conversing with several very knowledgeable people en here on this board.on this board, and with the EDGE motorcycle club in Lawndale, California, I proceeded to complete some mods described here on this board.

1. The Free Flow Air Filter Mod

This modification did not require a K&N, or any other aftermarket filter. I will eventually get around to replacing the modified stock filter to a K&N, but in reality, not much improvement as far as horsepower would be gained. Looks wise, yes, performance wise, .. not really. So I removed the seat, took a look at the restrictive airbox, and proceeded to find an easy way to remove it. I found one - A big hammer. After (very carefully, and after removing the air filter) smashing the crap out of it, it slid quite nicely out of the frame (in a few pieces). Ok, so with that done, I looked at the rubber connecting tube that once led from the carb, to the airbox. Ok, so it looked as though I could take the stock air filter and place it flush against the rubber piece. There are 4 little nubs on the air filter where the diverter piece used to be. I sliced them off with a razor so that the face of the filter was flat, and would sit against the rubber hose flush. If you don't do this, you WILL get some leakage, a good seal wont be made. I then wedged the air filter in-between the carb, and the toolbox/storage compartment, and tada! a free flow air filter. =)

2. The Holes In The Stock Exhaust Mod

Ok, so all looked good, I put the seat back on, proceeded to clumsily drill 8 1/8" holes around the outside ring of the baffle plate on my stock exhaust.
I hit a sort of flange cutting into it, but didn't cut through it. In any case the holes were in, and my 1/8" drill bit, and 9v drill were exhausted. I promptly returned them to home depot =) ... and then ran back home. Turning the engine on, I got a roar. not a tiny one, but a good sized growl. Wow. All I can say is wow, what a difference. But I did get a little popping. It sounded great overall however, and concluded that this mod was worth it. I considered de-flanging the pipe, but was advised my a great motorcycle mechanic against it. Not enough back pressure, an odd sound, and just not worth the trouble. I think for now I'm fine with this until I get a new bolt on pipe all together.

3. The Carb Adjustment

Well, it was time for the test ride, and WOW. After riding this new set up, .. it ran like ... Shit.
Literally a piece of dung. In fact, it seemed to change the way everything ran altogether. Not great. It was running way too lean, and this was not good at all.
Taking it to Edge Motorcycle Club in Lawndale, Ca fixed all of this. In an hours time, my buddy opened everything up, and proceeded to modify the carb.
Now I described what many have said on this board as far as how to rejet their carbs, and went into detail as to how he should go about it. The only problem is, that the carb needle was stock, and did not have grooves to move the washer, or slider down into. If I would have had a jet kit, this might have been different, but it was stock, so he decided to do a few other things. First, he drilled out the main jet to make it a 150th jet. He then adjusted the air screw to tune the pilot jet circuit. He had to make several holes where there weren't any, to access the adjustment screws, but he decided that this tune would be just fine and didn't require the needle adjustment.

Now came the road test. He started it up. Woosh! Vroom! MUCH DIFFERENT. The bike, I kid you not runs MUCH better than stock, my top speed has increased from a stock 55-65 to 65-70. The power boost is amazing, and It is a much better ride in every way. I am impressed. Wow.

The next mod I was suggested to give it was an upgrade from a 15 tooth front sprocket, to a 16 tooth. With this upgrade, I will gain a better top speed, and the loss of low end power will be so slight that wouldn't matter. Especially for a 250cc bike. I'm told I should hit 75-80 after the sprocket mod, a K&N, and a new pipe. This is good enough for me, as I will be riding this on the highway in Florida where the speed limit is 55mph. Most people cruise at 65. That's all right with me.

Removing The Rear Seat Mod:

Too easy to explain.

I do ahve a question. Does anyone know of the largest, and best K&N to use on this bike, the size needed, and any adaptor hose used?
As well, what bolt on pipes would look/work best on this fun little bike? I have head a lot about straight pipes, and others, but can anyone reccomend a few? I dont want it much louder than it already is now, and it does not need to be a Harley, but some more free flow, as well as a deep rumble sound as opposed to a 250cc sound would be awesome.

Anyone?

Thanks guys. =)

I love my bike, and as a fist time rider, Im already outgrowing it. My next bike I think is going to be the Suzuki M50 for sure.

http://img251.imageshack.us/img251/8487/gz250002dj1.jpg
http://img251.imageshack.us/img251/5082/gz250003ps6.jpg
http://img251.imageshack.us/img251/3851/gz250004uz2.jpg
http://img251.imageshack.us/img251/9218/gz250005nx0.jpg
http://img412.imageshack.us/img412/7663/gz250006ly0.jpg
http://img412.imageshack.us/img412/15/gz250007mu5.jpg

[Jordan310]

YES!

With just the needle shim, the free flow stock air mod, a re-jet of the carb, and drilling holes, I got my GZ250 on the Los Angeles Freeway today up to 80 Mph (More like 78-79Mph.).

Yes, it is possible, and no, I havent even done the freeflow exaust yet. I plan on putting a large K&N filter on it, finding a perfect free-flow pipe, getting a custom made jet-kit from The Motorcycle Doctor in Torrance, and drilling out the carb a bit more making the jet larger. As well, I am going to add a 16 sprocket front disc, and add a better rear tire.

I want to put in a hotter cam, and then have it tuned once more on the machine.

I have no doubt that this machine will reach 85Mhp easy after these mods. And get this, .. its not even broken in yet ...
I love this bike.

:neener:

[bigfour]

Nice bike, I don't have a reccomendation for a good exhaust but from personal experience, a straight pipe would do real well on this bike as long as you've got the carb set up right. I cut off the exhaust on my bike and it sounds real good--a nostalgic roar, nothing a cop will pull you over for.
For now, I've put a restictor cap on my exhaust to provide a little backpressure until I've got the carb fine tuned. If your bike runs good with the exhaust drilled out that much, you might not even need to make any adjustments moving up to a freer flowing exhaust.

[Jordan310]

Honestly, the bike runns pretty lean still!
It still pops on occasion, and has a tendancy to stall untill super warm. It baby backfires a few times ...

The holes are ok, but no, putting a better pipe on it would do much better for it.
I was told to find a good aftermarket 2 in 1 that will let the thing breath like crazy. All the carb adjustments can be made after that, and its not that difficult to drill it. The bike will scream.

I do notice that when hitting about 70-78Mph in 5th gear, the bike tends to whine a lot. Not too bad, but it does shake.
Not like crazy, but it gets a little squirly.

DOES ANYONE know where I can find THE BEST aftermarket pipe setup, and at the least, just the exhaust. Nothing fancy, just good looking and clean, and plain.

Also, does anyone know the correct K&N filter that might lend itself well to this carb? The bigger the better?
One more thing.

I relocated the horn to where the orage reflector was, .. just looked better. Then I tested it.
When I pressed the horn, it just barely made a sound. After that, the lights dimmed ever so slightly. Every time you press the horn button, the lights dim just a bit.

Any idea what happened here?

A horn is a good thing to have on L.A. freeways. :sad:


EDIT: I had the carb adjusted a little bit, and its all fixed.

[caroledee1]

I finally did the needle shim mod last week. I did the 16 tooth sprocket one day and the needle shim the next. I like the lower gearing with the 16 tooth

but definitely felt a lack of power. The needle shim brought that power back and my mpg has improved about 4 mpg. One thing I don't believe was mentioned

in the "How To" was : Loosen clamps in front and back of the carb. Then tilt the top of the carb to the right side(normal riding position) for better access.

[Jordan310]

The needle shim is ok, but the bottom of the needle may not seat propery if done as specified in the instruction manual.
Best to rejet. Bigger jets, and tune. =)

[Badbob]

After months and thousands of miles of riding with the needle shim mod here is my cost in mpg:


Before - 64.92 mpg
After - 56.88 mpg
Difference - 8.04 mpg

[Gadzooks Mike]

And how is the difference in running and ride?

[Badbob]

And how is the difference in running and ride?

Smoothed out the acceleration flat spots. Thats about it.

[Regular Guy]

FYI good info on setting up a carb mod.http://www.factorypro.com/tech/carbtune.html. Hope this is helpful!

[jonathan180iq]

Here is a photo showing the placement of washers that have been in described in the first few messages of this thread.
http://www.postimage.org/aV209bri.jpg (http://www.postimage.org/image.php?v=aV209bri)

NOTICE. My bike is a 2006 and I do not have the selectable circlip grooves that have been described in other posts on the forum.

[Canuck]

So far i have done the 16t and the Needle Shim

Having ridden awhile with the 16t I decided to try this shimming idea.

I'm pretty happy with it.. cruising in 5th gear is smoother and toned down abit
At minimal throttle before the shim i went from 60 kms down to 55 km at the same setting so it was definitely a great change.

not sure how i feel about the loss in mileage as noted by badbob but we will see..

[Easy Rider]

not sure how i feel about the loss in mileage as noted by badbob but we will see..

That depends a LOT on your riding conditions and habits.
I predict that, unless you keep really good records, you won't notice any significant difference.
I didn't......with just the 16T and no carb mods, that is.

[Canuck]

I took the washer and put it underneath...

Is it better to keep the stock washer on top and get another one for underneath...does it matter or will it be alright with the switched stock washer...??

any bad experiences yet with the needle shim modification? or is everyone all thumbs for it ?

[Badbob]

I switched the washer position about 18,000 miles (guess) ago. No problems yet.

[Canuck]

Switched back my washer position to original and now only with a 16 tooth modifying the bikes gear.

Just wasnt worth the lost gas mileage and probably isnt great for overall longevity of the bike.. ? perhaps

I did like the flat spots eliminated but.. it wasnt that great of a different overall.

[Easy Rider]

Switched back my washer position to original and now only with a 16 tooth modifying the bikes gear.


OK, so now that you are getting closer to stock, how does your idle speed act? Is it a LOT different when thoroughly HOT than it is when just coming down off the choke?

[Canuck]

Easy, since the valve adjustment the bikes only problem is needing new rear brake cables and rear hub rubber shock absorber

running great at idle but i do miss the flat spot elimination.

not gonna bother changing it back
and the next sprocket i have in the toolbox is a 15t so.. this summer will be stock riding all the way.

Something tells me i shouldn't have messed with a good thing. haha

Ill see how it goes and see if i can keep my hands off the shim mod.

[Easy Rider]

and the next sprocket i have in the toolbox is a 15t so.. this summer will be stock riding all the way.


Have you decided that you don't like the 16T......or are you just cheap? :biggrin:

[Canuck]

hahahah no not cheap Easy.

I always think back to Pacific Motorcycle schools fleet of GZ's

I know most motorcycle schools obviously have the know how on what to do with a GZ to keep it running optimal. Lesson after lesson those bikes have to be near perfect.

My GZ does not ride like the GZ i rode back then.

I know it is my own fault. 90 bucks an hour at the shop just doesn't suit my budget when something goes wrong everytime. Perhaps frugality does play a factor in what happens to the bike. I try my best with the greatest of intentions for the bike. Obviously somewhere along the line Ive neglected the wrong problem(s).

I just know that those bikes had a 15tooth and were well maintained or pulled off the lineup if faulty. Mark was a 5 time super bike champion who has his own Q and A on the schools website. I am sure his decisions were best among anyone I have met or discussed the GZ with. However he is a busy man whom i do not want to bother on a constant basis when i have problems. Opening to a variety of people who have shared my beginner status and are on the same level if not a few tiers higher seems more plausible and to also allow others to read a learn from my mistakes and what led to a solution seems beneficial.

I want the bike the way that school ran theirs if not closer to it. I liked the 16tooth with the Shim Mod.
But I THINK you can get a similar ride that was originally designed for the bike ( by the engineers who built it) without wondering if your screwing the bike up in the long run.

Maybe there is a reason the GZ has been unchanged and unmodified from 99-present....

[Sarris]

Maybe there is a reason the GZ has been unchanged and unmodified from 99-present....

Yep.

:plus1:

[Easy Rider]

I know most motorcycle schools obviously have the know how on what to do with a GZ to keep it running optimal. Lesson after lesson those bikes have to be near perfect.

My GZ does not ride like the GZ i rode back then.



Me thinks you worry too much......or about the wrong things.

The bike school has NO reason to be making ANY changes to their machines....NONE.

Of course it doesn't ride the same with a different sprocket; that's the whole point.

By all means, if you don't like the altered gearing, go back, but if you are doing it out of some twisted notion that you might be "hurting" the bike somehow, forget it; it isn't.

Mine is not idling right at the moment. Do you think I should put back the 15T sprocket? :roll:

[alanmcorcoran]

(Warning, piling it on...) I don't know about the rest of you guys, but the bikes in my class ran ok, but beyond that, they were thrashed! No mirrors, gas tanks looked like used aluminum foil, bent bars, stuffing coming out of seats, chipped controls, etc. Each day, they would trot out 36 bikes or so, and inevitably four or five wouldn't even start, and one or two would give up the ghost duing the session. There were a couple of dirt bikes that looked like they'd been driven into trees. There was a little bit of jostling in the morning for people trying to get on the least piece of shit bike. "Hey, I rode that one yesterday!" "Well, I'm riding it today!"

(I, on the other hand, was sitting astride my brand new silver/grey GZ steed in pristine condition! Everyone else in the class had bikes that were too big to be used. Oh, the irony!)

[mrlmd1]

Those bikes in LA were probably impounds or stolen/police donations - my class in Florida had pretty much pristine Rebels and a few dirt bikes. All started, ran well, were not dented or beat up, and we had the same bike on day 2 as day 1.

[buck-gz]

I did the needle shim mod yesterday. WOW! I wish I had done it sooner.

What a difference a little piece of steel in the right place makes. The flat spot in the power is gone, and I have more confidence in the bike. I may try an upgraded exhaust and new jet in the carburetor.

Kudos to all of the contributors on this topic. Well done!

:2tup:

[Sarris]

I'm interested in hearing how much your gas mileage drops. Most report a 10+ mpg loss.

:)

[buck-gz]

I have read about that. I will keep track and send an update. :??:

[tommygun]

can someone tell me if after the needle shim it is necessary to open the air filter up for increased airflow?

[tommygun]

The reason I ask is that I just did the 16t sprocket mod and am having difficulty getting up the most simple of hills here in NE Georgia. I love the low rpms that I get with the mod but miss the little bit of power I got with the 15t in 5th gear. Will the needle shim help with this? What is the difference in this mod vs the "gz power increase" mod listed elsewhere?

[Easy Rider]

The reason I ask is that I just did the 16t sprocket mod and am having difficulty getting up the most simple of hills here in NE Georgia.

Well you may not be a good candidate for the 16T
.....OR......
you just need to "adapt" your riding style a bit.

IIRC, you can do 50 mph with no sweat in 4TH gear and even 60 for short periods. That gives you a jump on 5th and might solve most of your problem. You also need to learn to anticipate the hills and build up a little extra speed going in. I found that I could pull most hills in 5th but had to run it up to 60-65 going IN to be able to maintain 55 going up.

If you change to something like a K&N filter, you should consider doing ALL the power mods; needle shim, jet change and idle air adjustment........but even with all three, most folks don't notice much difference. If you are not experienced in working with carbs, I would recommend that you NOT try it yourself. The actual changes are fairly simple but getting it all back together right can be somewhat of a challange.

P.S. As there are NO hills to speak of in Illinios, my experience was on a trip to Atlanta. There were some places that I had to run in 4th.....but not many....if there was no traffic pushing me to go more than 50.

[tommygun]

After the needle shim is it nessesary/helpful to modify the air filter? or shoul a complete rejeting be done first?

[Easy Rider]

After the needle shim is it nessesary/helpful to modify the air filter? or shoul a complete rejeting be done first?

You need to go back and read the carb modification threads carefully.
Those who have actually DONE it know more than those of us that have NOT !!! :roll:

IIRC, if you ONLY do the needle shim, you don't really need to mess with anything else.

After that, the jet change and idle air screw adjustment goes along with better air flow; you should consider those as a package and be prepared to do both together.....if you do any part of it.

[tommygun]

Well I shimmed the needle the other day and noticed alot more throttle overall. I also did the 16t sprocket mod the day prior to shimming the needle. Best results came from going back to the 15t sprocket and keeping the needle shim mod. I am much happier with the bike. It is more confident in all gears. I am still toying with doing the other jets and installing a K& N filter. my goal is to see if I can maintain the speed (or gain some) while going up a hill. i live in the foothills of NE Georgia and go up and down many hill in my commute. The only other hope is to just get a bigger bike. :??: :??:

[tommygun]

Easy, I have been riding as you suggested ( accelerating to a high speed before I approach the hill) for a while now and my complaints/ questions reflect still riding the way you suggested.

[Easy Rider]

Easy, I have been riding as you suggested ( accelerating to a high speed before I approach the hill) for a while now and my complaints/ questions reflect still riding the way you suggested.

The GZ is what it IS. No matter what you do to it, it will NOT accelerate UPHILL in 5th gear; it just won't.

OTOH, it won't completley choke either so you have 3 basic choices:
1) Learn to live with the limitations.
2) Put the 16T back on and shift to 4th for going up hills.......and #1 too.
3) Get something different that will hold the hills.

[tommygun]

Have learned to live with it, trying to like it.

[Sarris]

The real solution to your problem is another 250cc or so. Maybe a Kawayamazuki 500cc (or larger) would be better for your needs.

There are places where a GZ is just too damn small. Being 6'-1" and 280 lbs, I run into that occasionally here on the Central Florida hills.

If this is ongoing daily really-piss-you-off issue, start looking. With the economy in the crapper, this is a good time to buy a used bike.

I would suggest keeping the 'ol GeeZer though, as you can never have enough bikes.

:rawk: :lol:

[buck-gz]

I'm interested in hearing how much your gas mileage drops. Most report a 10+ mpg loss.

:)

Okay. Post needle shim modification, I tracked my gas mileage. After many miles and several fillups, here are my results:

MPG per fillup:
==============
1. 68
2. 65
3. 65
4. 64
5. 65
6. 65

Average = 65.3

I was averaging between 65 and 70mpg before the modification. I am seeing about a 7% drop in gas mileage now.

I drive a regular commute each day and take joy rides over the same roads. Most of my driving is at speeds between 40-50 mph. Maybe 20% is open road, 50-55+ mph. The terrain I drive on is generally flat with some rolling hills.

I am very happy with the performance increase - the slight drop in mileage is small price to pay.

[Blackbird]

I'm interested in hearing how much your gas mileage drops. Most report a 10+ mpg loss.

:)

Okay. Post needle shim modification, I tracked my gas mileage. After many miles and several fillups, here are my results:

MPG per fillup:
==============
1. 68
2. 65
3. 65
4. 64
5. 65
6. 65

Average = 65.3

I was averaging between 65 and 70mpg before the modification. I am seeing about a 7% drop in gas mileage now.

I drive a regular commute each day and take joy rides over the same roads. Most of my driving is at speeds between 40-50 mph. Maybe 20% is open road, 50-55+ mph. The terrain I drive on is generally flat with some rolling hills.

I am very happy with the performance increase - the slight drop in mileage is small price to pay.

Buck GZ ...
I've done the needle mod, the air intake, the jetting and exhaust. I also put in a NGK Iridium spark plug. That coupled with the 16 tooth sprocket makes this a sporty bike. I know of no one that has done all of these mods and regretted it. My bike Raven has never ever complained to me. I still have a couple of add ons to do to make it my special buddy. Go for it! :rawk:

[tommygun]

My miliage seemed to improve after the needle shim mod??? Before i would have to switch to the reserve tanks at about 185 miles now I switch at 200???? (and I know I shouldn't run it dry just a trial test)

[bonehead]

I did my needle shim and installed a 140 main jet and my milage droppped 10mpg. Don't know what the deal is. Thinking about reversing the procedure to gain back my mpg.

[Easy Rider]

I did my needle shim and installed a 140 main jet and my milage droppped 10mpg. Don't know what the deal is. Thinking about reversing the procedure to gain back my mpg.

A few others have had a similar experience but don't give up until you've run at least 3 tanks through.

What ELSE have you done?
16T
K&N
muffler
????

[jonathan180iq]

The deal is that by increasing the jet size you are letting more gas into the engine than before. It's very commong to experience a loss in gas mileage when rejetting for more power. Try backing off just slightly on the jet size and see if you can maintain a proper mixture. You can find a balance between power and economy. Selecting jets isn't a written-in-stone procedure. If they make a 138, for example, I would try that. If you're get a lean mixture with a 138, then you need to stay with the 140 and you'll just have to live with the loss in mileage.

I just recently down jetted my scooter and I saw a 17MPG increase. Talk about exciting. Top speed and engine "smoothness" stayed the same. Some clown before me had it over jetted. I must be a clown too, for not checking it sooner. I dropped from a 125, which was only slightly rich, down to a 115, which is perfect.

[VTXorcist]

By the way, for those who don't know their way around a carb, like me, page 11 of the Parts manual (see the first post in the Troubleshooting section to download it) has an exploded diagram of the carb. It really clarifies the instructions at the beginning of this thread, especially about the springs and plastic "thing". ;)

[emory70]

if you change the intake and exhaust to get more airflow, you are just helping the engine breathe better. carb mods are only helping to correct for that change. if anything, there should be an increase in gas mileage. if it decreases, i would wager that it's because the new power encourages more aggressive riding.

[Easy Rider]

if anything, there should be an increase in gas mileage. if it decreases, i would wager that it's because the new power encourages more aggressive riding.

No doubt that's part of it but making the mixture RICHER and allowing more of that richer mixture to "flow" through the engine pretty much automatically means that you are gonna use more gas in the process.

None of the changes described here makes the engine any more efficient.

[emory70]

how can freeing up the intake and exhaust not make the engine more efficient? getting more air into and out of the engine is the definition of increased efficiency. no 4 stroke engine needs exhaust backpressure to run properly. the illusion of needed backpressure is just a sign of a poorly tuned exhaust.

[Easy Rider]

getting more air into and out of the engine is the definition of increased efficiency.

What ??

No it isn't.

The definition of "more efficient" is getting more power or mileage out of a given volume of fuel.

Real world reports from riders who have done the mods outlined here indicate, without exception I think, that the engine "feels" like it has more power and runs "better" but not a single one has reported an INCREASE in fuel mileage.......or even exactly the same. The difference isn't much but it is always a bit lower. That tends to indicate that the extra power they achieve requires a little extra gas to get it.......and that is not increased efficiency.

[blaine]

The definition of "more efficient" is getting more power or mileage out of a given volume of fuel.

Real world reports from riders who have done the mods outlined here indicate, without exception I think, that the engine "feels" like it has more power and runs "better" but not a single one has reported an INCREASE in fuel mileage.......or even exactly the same. The difference isn't much but it is always a bit lower. That tends to indicate that the extra power they achieve requires a little extra gas to get it.......and that is not increased efficiency.
:plus1:
Increased performance-Decreased efficiency.
:2tup:

[Water Warrior 2]

how can freeing up the intake and exhaust not make the engine more efficient? getting more air into and out of the engine is the definition of increased efficiency. no 4 stroke engine needs exhaust backpressure to run properly. the illusion of needed backpressure is just a sign of a poorly tuned exhaust.
Not looking for a war of words here but you are so wrong. Some high end cars actually have a variable back pressure system to promote better scavaging at different RPM ranges.

[emory70]

i could see having some type of system like that to make a car with a very narrow powerband easier to drive in the real world. but it's a crutch, not a power maker. they would need that extra scavenging cause the engine is out of its happy place.

maybe most or all people here that have changed the muffler and/or air filter on their bikes have then lost some mileage after retuning the carb. how did they tune it? on a chassis dyno? how else are you gonna REALLY tune the engine?

[Easy Rider]

how else are you gonna REALLY tune the engine?

You "mess" with the needle and main jets until it runs better............or take the recommendation of someone else who has already done that.

We may have had one nut....mmm..err..rider here who did some dyno runs but I doubt it.

[emory70]

i guess i'll live with my muffler for now, but that stupid $40 air filter has to go.

[Water Warrior 2]

i could see having some type of system like that to make a car with a very narrow powerband easier to drive in the real world. but it's a crutch, not a power maker. they would need that extra scavenging cause the engine is out of its happy place.
Talk to the designers of BMW car engines. Their variable back pressure system keeps the engine in it's happy place over a very wide RPM range. This is actually old technology now and I would not be surprised if a large % of cars have this to meet emissions while still providing performance and economy

[blaine]

i guess i'll live with my muffler for now, but that stupid $40 air filter has to go.

A good replacment is the Hiflo-Filtro-HFA-3503 at less than $20.00.It is listed for the GS 500 but is a direct fit.

:lol: :roll:

[Easy Rider]

i guess i'll live with my muffler for now, but that stupid $40 air filter has to go.

A good replacment is the Hiflo-Filtro-HFA-3503 at less than $20.00.It is listed for the GS 500 but is a direct fit.

:lol: :roll:

And does NOT require re-jettting, if I remember correctly ????

The stock filter has enough filtering area that they should be good for MANY years of light to medium distance riding if cleaned occasionally. At $20, I'd say that's a good buy if you don't have to screw with any other settings. :tup:

[blaine]

A good replacment is the Hiflo-Filtro-HFA-3503 at less than $20.00.It is listed for the GS 500 but is a direct fit.

:lol: :roll:

And does NOT require re-jettting, if I remember correctly ????
:tup:

Does not any rejetting,drop in and go. :2tup:

[Water Warrior 2]

After 5 years and 50,000 kms my Vstrom air filter is still good. I don't look forward to replacing it because it is a one of a kind and only Suzuki has it. Waiting for Hi-Flo to make them at a cheaper cost and crossing my fingers.

[Boon13]

Would the needle shim mod work on a GN250?

[blaine]

Would the needle shim mod work on a GN250?
Yep,same carb. :) :cool:

[Road_Clam]

Too funny I just read this tip, and one of my first mods to any bike that has a slight lean stumble off idle and into the mid range is to shim the needle. Modern bikes come so EPA lean with respect to low speed jetting they run like absolute garbage in cooler temps (like we have up here in New England). I drove our new GZ for about 1/2 hr in colder temps and knew right away my carb need some richening. I have a bunch of 3mm X .020" washers I got from Radio Shack, and they work perfect for shimming needles. I also pulled the "epa" plug for the air fuel screw, and added 1/2 turn CCW for some much needed cold starting ease. Now even if it's 40F, our GZ fires right up on 1/2 choke as soon as I hear elevated clean rpm's I shut the choke off and the engine purrs perfect. No mid range stumble either. I've shimmed needles and many times also have to bump the pilot jet(s) one size richer too, but so far doesn't seem like the GZ will need a richer pilot jet. Great tech thread !

[Road_Clam]

how can freeing up the intake and exhaust not make the engine more efficient? .

Easy. The cylinder head port design is most likely the "bottle neck". A combustion engine is simply an air pump. In theory the more air you let in, the more air you need to let out. So one would think that adding a free flowing exhaust, a K&N filter and re-jetting the carb would yield flow and hp gains. BUT if the valves and the intake and or exhaust port design are already at max flow, all your other intake and exhaust flow performance mods are useless. I would bet my left *** that if a GZ owner sent their head out to be velocity ported, AND added a exhaust, filter and re-jet, now I would bet you would feel a substantial difference. But again, the GZ was not engineered to be a stop light to stop light beast... LOL

[blaine]

Too funny I just read this tip, and one of my first mods to any bike that has a slight lean stumble off idle and into the mid range is to shim the needle. Modern bikes come so EPA lean with respect to low speed jetting they run like absolute garbage in cooler temps (like we have up here in New England). I drove our new GZ for about 1/2 hr in colder temps and knew right away my carb need some richening. I have a bunch of 3mm X .020" washers I got from Radio Shack, and they work perfect for shimming needles. I also pulled the "epa" plug for the air fuel screw, and added 1/2 turn CCW for some much needed cold starting ease. Now even if it's 40F, our GZ fires right up on 1/2 choke as soon as I hear elevated clean rpm's I shut the choke off and the engine purrs perfect. No mid range stumble either. I've shimmed needles and many times also have to bump the pilot jet(s) one size richer too, but so far doesn't seem like the GZ will need a richer pilot jet. Great tech thread !
Exactly the same with mine.Couldn't believe the difference in cold starting.You wouldn't think it was the same bike.Oh.Welcome to the family.
:) :cool:

[golem]

I did the needle shimming yesterday and today, while riding, my bike stopped for no reason, it just started to make less noise then stopped all together. I was able to start it again after a couple of tries and get back to work. Do you think it might be related?

[jonathan180iq]

While doing the shim, you mess with a couple of things that could cause an air leak. A big enough air leak and you loose vacuum to draw fuel, which would eventually kill the bike.

Make sure your vacuum hoses are connected.
Make sure your carb boot is secure
Make sure you didn't kink the fuel line
Make sure you didn't pinch the rubber diaphragm under the black plastic cover on top. (That happens a lot)

[golem]

Ok thank you !