No Acceleration at 40MPH

[anesde]

I did a search and couldn't find anything so I figured I'd start a new topic. I've been getting to know my 2003 gz250 in the past month and from what I've read about top speeds and acceleration I think something is wrong. On flat roads the bike does not get above 45 even with wide open throttle in fourth gear.

It wasn't running when I bought it but all I did was put a new battery, new spark plug, and dismantled/cleaned/reassembled the carburetor. I did go an extra half turn on the pilot screw and shimmed the needle (not a true shim, just switched the position of the washer per one of the topics on this forum). I also changed the oil to synthetic (bike had about 6000 miles when I bought it). The engine sounds good but power doesn't translate to the wheels.

I weigh ~170 lbs so I don't think its a weight problem. I did take the windshield off but I don't think wind resistance should keep me from hitting 60-65.

At a loss for what it could be - any suggestions?

[Water Warrior 2]

I wonder if the air filter is plugged up a fair amount. To check the filter it must be removed and inspected. Air flow is from the inside to the outside( reverse to what we normally see in filter systems). The inside gets dirtier than the outside.

The airbox is a sealed system. You can't drill holes in it to increase airflow, all you will accomplish is feed dirty air directly into the engine.

[anesde]

Changed the air filter and still have the same issue. Went from 2.5 turns on pilot screw to 1.75 turns and no change either.

From what I read it seems that this could be a symptom of a slipping clutch? I don't really know how to gauge whether or not it is slipping. I don't have problem shifting gears but I do notice that between halfway and full throttle the engine revs up but doesn't actually move any faster. Any thoughts?

[Fawlty]

I don't really know how to gauge whether or not it is slipping. I don't have problem shifting gears but I do notice that between halfway and full throttle the engine revs up but doesn't actually move any faster. Any thoughts?

OK, find a long uphill stretch of road, get into 4th gear at about 40mph or 5th gear at about 50mph, then try and accelerate using full throttle, if your revs increase, but your speed doesn't, your clutch is slipping.

[Water Warrior 2]

Ah, more info to work with. Likely as suggested..........clutch adjustment needed.
Secondly...........did you do an oil change and exactly what kind of oil did you use? You must use moto specific oil or the clutch will likely slip. Must be a JASO certified oil for wet clutches.

[5th_bike]

When adjusting the clutch cable, keep in mind that the clutch handle (grip) needs to be moving freely about 1 cm at its tip.

[blaine]

When adjusting the clutch cable, keep in mind that the clutch handle (grip) needs to be moving freely about 1 cm at its tip.
Should be about 1/2" (12mm) at outer tip of clutch lever.About 2 to 3 mm between inner end & perch. ;) :)

[jonathan180iq]

Can the bike rev up, strong and loud, if it's in neutral?

[anesde]

Changed the oil two months ago and used synthetic royal purple 10w-40. Also changed spark plug back then - guy at Napa told me it was NGK DCPR8E

I thought it was the oil so I changed back today to Castrol GTX conventional 10w-40. Only had about 70 miles with the synthetic - what a waste!

Anyway the bike did not perform any better so I thought maybe the spark plug. Looked up the spark plug and found the internet says it's NGK DR8EA, not what I have in there. Took the old one out and it's black - covered in soot. Not wet which is what I thought I might find. Took her for a quick spin after changing the plug. I think I notice a slight uptick but it got dark so I'll have to wait until tmrw

[anesde]

Also I did check the clutch and it's correct. And yes it revs up strong and loud. Too loud actually, I changed the idle screw to the bare minimum. Do you think that may have something to do with it?

[raul10141964]

the idler screw is not your problem set it 2.5 to 3 turns to have a good idler and easy cold start.
check the main jet and make sure the slider move freely up an down
carbon build up may prevent the slider to open all the way

[Water Warrior 2]

Changed the oil two months ago and used synthetic royal purple 10w-40. Also changed spark plug back then - guy at Napa told me it was NGK DCPR8E

I thought it was the oil so I changed back today to Castrol GTX conventional 10w-40. Only had about 70 miles with the synthetic - what a waste!

Anyway the bike did not perform any better so I thought maybe the spark plug. Looked up the spark plug and found the internet says it's NGK DR8EA, not what I have in there. Took the old one out and it's black - covered in soot. Not wet which is what I thought I might find. Took her for a quick spin after changing the plug. I think I notice a slight uptick but it got dark so I'll have to wait until tmrw
I think you answered your own question, slipping clutch. Both oils you mentioned are for car use, not bike use. You must use a JASO certified oil. Look on the oil container for the designation. Shell Rotella, Dino or Synthetic will work fine and are the cheaper than most others. Had excellant results in 2 of our bikes with the dino variety.

[gz4me +]

I agree with Water Warrior 2. Wrong type of oil. I have dealt with this problem in the past while working on friends bikes. One was a Honda Rebel and two were Suzuki. Problem went away after changing to correct oil.

[anesde]

I found it hard to believe that oil was the only culprit. Bought new clutch plates and took the clutch apart this morning. Clutch plates had nothing on them and friction plates were scoured and bluish. I didn't have new friction plates so I put it back together with the old ones and new clutch plates. Took it for a quick spin and she's still slipping.

I had bought the clutch plates off amazon for 35 but the entire assembly (new springs too which I don't think I need - old ones look good) is more like 135. Anyone know of a vendor that just sells friction plates?

Bike only had 6300 miles when I bought it so previous owner must have treated it terribly.

[spldart]

If the steels were blue'ish then they've been overheated. At least that was my experience from 15 to 20 years ago when I used to work on bikes all the time. I would just take extremely fine sandpaper and give the steels a very light roughing up. After you clean the old oil off first.
Did you presoak the friction plates in fresh motorcycle motor oil?

I have put , a long time ago, car motor oil in a wet clutch bike and felt the clutch go from 'just fine' to 'slipping kinda bad' nearly instantly so oil is a serious issue..

[spldart]

A slipping clutch diagnosis is easy. Try to launch the bike. Does the motor rev out while the bike barely moves? Or do you end up with a stalled engine?

Obviously show care not to get to fast, flip bike or otherwise case it on this test.

[Water Warrior 2]

Rather than use fine sandpaper you should use emery cloth that is made for metal. That and varsol to aid the cleaning. Then use oil to clean the residual off and soak in fresh oil prior to assembly.

[anesde]

Yes I did soak the plates overnight. Used motorcycle oil this time. Going to bite the bullet and buy the whole new assembly instead of messing around with trying to clean up the current plates.

I still find it hard to believe it would have no difference after I changed up the clutch plates so I'm double checking all adjustments first.

[spldart]

I use that 1000 wet sand stuff.

[Water Warrior 2]

I use that 1000 wet sand stuff.
Yup, that is fine enough. Never ever would have thought of wet sandpaper. :doh:

[spldart]

I've had to replace clutch basket springs once. It was a 'beginners bike' that I started on back in the early nineties. An 82 Kawi 305 csr. Good bike. Anywho. The springs had a fairly significant number of miles on them when I rebuilt the engine. Once the rebuild with: bore out .5mm with new pistons/rings, shave the head, new valves with machining, port and polish, slight degree of cam and re-jet after k&n's i found the old clutch springs were an issue.
And even though it sounds like I did a lot I only increased top speed from upper 70's to the lower/mid 80's mph.

I guess what I'm saying is springs could be an issue.
Miles of use?
Contaminated plates can be an issue.
You seem to have eliminated that.

Can the lever arm at the shaft on top of the case be moved slightly by hand?
If you have taken up so much play that you can't 'wiggle it just a little bit' then...
imho, you have taken to much play out of the connection between handle and
clutch engagement.

Again. Bluish plates screams overheated from slipping.
Slipping by improper oil.
Slipping by improper adjustment.
Slipping by weak springs.

Just a thought. Has anyone been in this motor case before you?

Perhaps improper reassembly or missing part is causing this??

[Lilfrog]

Did your issue resolve? I just picked up an '08 with 1,300 miles. Changed the oil with Rotella Syn. I'm having the same issue. I can't get Suzi going faster than 45mpg...

[anesde]

Not yet. I took the whole thing apart again yesterday and the put on new steel plates on. Triple checked that all the parts were in there and in the correct order and then put everything back together.

Literally NO change in the way it rides.

I just spoke with one of my coworkers who works on his own bikes and he mentioned the possibility that the the "Screw" (#22) may need to be adjusted into the "Piece, Clutch Push" (#19) to tighten the plates closer together. See schematic assembly attached.

No time tonight but I'll be trying that later this week.

[anesde]

Also, I think part of the problem is that the manual did not convert the required torque correctly, nor apparently use the correct units. It specifics 10 N-m for the 4 bolts that hold the clutch springs in and says that's the equivalent of 7 lb-ft. Pound-feet is a not the same as foot-pound and I believe they intended to use foot-pound (measure of torque) not pound-feet (measure of work) here. Regardless, 10 N-m is really 7.37 ft-lb which is 88.5 in-lb.

My torque wrench is set in in-lb with an alternate setting in N-m. Originally I set it for 84 in-lb (7ft-lb) when I just installed the friction plates. After I put in the steel plates I set it to 88 in-lbs (9.94 N-m) which is as close to 10N-m as I can get without going over (next measurement is 89 in-lbs which is 10.06 N-m).

I seriously doubt 9.94 to 10 is enough to keep these things from properly engaging but I really don't know - its just thousands of an inch that makes the difference from slipping or engaging.

I think part of the problem is the rod that I mentioned above - the manual says to set it tight then back it out 1/4". I'll try that as well as going to 89 in-lbs (10.06 N-m) and hopefully this does the trick.

If not I think I may go crazy.

[Water Warrior 2]

I think part of the problem is the rod that I mentioned above - the manual says to set it tight then back it out 1/4". I'll try that as well as going to 89 in-lbs (10.06 N-m) and hopefully this does the trick.

If not I think I may go crazy.
Thr clutch rod needs the 1/4 turn back. When the engine warms up the rod likely warms up too and expands to take up any slack or clearance. No clearance when cold will result in a slight clutch pull situation all the time..
Adjust the rod, then adjust the clutch cable and lever.

[Water Warrior 2]

Just a thought here. What is the oil like after a ride? With the bike upright and shut off.........is the oil level above the window? Is the oil full of bubbles or foamy looking? A bit too much oil may just cause something to slip due to air rather than a proper film of oil.

[anesde]

I put in the oil with a calibrated measuring cup and verified it's at the line while bike is upright.

I tightened the screw (the locknut was a BITCH to loosen) and backed it out a quarter turn per the manual.

For a recap I now have new friction plates, new steel plates, verified the screw is correct, and torqued the bolts holding the springs in to the right amount. Oil is conventional four stroke motorcycle oil.

The bike definitely runs better but is still lagging in acceleration. Part of the problem is I don't really know what it's supposed to run like (wasn't running when I bought it). However, I would suspect the gz250 could easily accelerate smoothly up to 60mph.

I paid closer attention and realized the throttle is unresponsive from half to full in 3rd/4th gear - that is when it's open halfway there is no change in engine sound or acceleration as I increase to full throttle.

The clutch was definitely as issue (old, worn plates and loose rod confirmed this) but now I think it may be something else as well. I cleaned the carb when I first got it and the only change I made was shimming the needle. I put a new sparkplug when I first noticed the acceleration issue - I'll check the gap but supposedly they come pre-gapped already.

Any thoughts? Haven't checked valve clearance yet but I don't think that would be causing this issue.

Any help appreciated! I bought the bike to learn about it so I don't mind all the problems but it would be nice to finally get it working right.

[blaine]

I suspect a dirty passage in carb that got missed.You can try some SeaFoam It may save you taking carb apart again. :)

[anesde]

Seafoam and a 25 mph ride and it runs slightly better but still won't go above 45.

I have a couple of coworkers who have a compression kit and a way to check the vacuum so I'll check that out tmrw.
Buying an inline fuel filter as well. If none of these solve this then I'm at a complete loss.

[anesde]

One thought - when I remounted the carburetor it was very difficult to ensure it was properly inside both rubber hose clamps (airbox and engine).

I'll double check theres no leaks once engine cools

[raul10141964]

Do you have the stoke air filter or a high performance
With high performance filter you need bigger main jet

[Lilfrog]

haven't checked valve clearance yet but i don't think that would be causing this issue.

any help appreciated! I bought the bike to learn about it so i don't mind all the problems but it would be nice to finally get it working right.[/quote]


I decided to check my valve clearance. I removed the exhaust side valve inspection caps and it looked like there was way too much clearance and that the gap would have to be smaller to be in the range of specs. I decided to look under the other inspection plate and to my surprise both adjusting screws and nuts! Not sure if when the prior owner had it's initial valve clearance adjustment that they somehow took out the screws and nuts and forgot to put them back in. I'm not sure how the bike was even running in the state it was in. I have to order parts and hopefully will have it back together next weekend. Crossing my fingers after the fix that I will be able to reach the top speed it's rated at.

[alantf]

I'm no mechanic, but is it possible (someone may come in here) that the locknuts came loose, the screws vibrated loose, and they've dropped somewhere in the engine? :hmm:

[Water Warrior 2]

Yipes !! Be glad the bike quit running and didn't turn into a grenade. Now you need to find those wandering parts.