Needle shim modification

[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.

[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]

Originally Posted by Gadzooks Mike

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!