Engine revs high when clutch pulled in?

[Time Bandit]

The bike is a 1997 RM250 and it ran fine for the first week i had it but now it started acting up. I was riding in 5th gear and wanted to slow so i pulled in the clutch, it revved uncontrollably high when i pulled in the clutch, i let it out and it was fine but eventually i had to pull it in to stop and it died. started up and it did the same thing in 3rd gear then wouldn't start after that. Any advice would be appreciated.

 

[truckster225]

My older suzuki used to do that. Im trying to remember what caused it. An airleak comes to mind.

 

[Time Bandit]

Yea my older 1980 DS80 used to do it to, no idea what causes it.

 

[truckster225]

Mine was a 79 DS100 (I think). Im almost positive it was an air leak. Check all your air related hoses and such for cracks, Also, make sure all your O-rings in the carb are in good shape and make sure the top cap on the carb is screwed on nice and tight.

Good luck!

 

[_JOE_]

Make sure the throttle slide is bottoming out on the idle screw and the cable moves freely.

If that checks out, look for an air leak between the carburetor and the cylinder. If all looks good there have a leak down test done to check the crank seals.

 

[Time Bandit]

I didn't check on the carb seals yet but I took the carb off and the piece between the carb and cylinder. This is what is happening-

With the spark plug in I will hand press down on the kick start and hear a hissing noise inside the cylinder, with the spark plug out the hissing goes away when pressing down on the kick start. So I think the spark plug is creating a vacuum but the pressure is drawing air from elsewhere. Is there supposed to be a hissing noise like I described? Here's a few pictures i took--

 

[whenfoxforks-ruled]

Now that your at this point. Are the reed petals closed all the way? Are there any cracks in the rubber intake manifold? You will need new gaskets and properly torque the reed/intake assembly back in. Check the throttle cable for being routed properly, kinks and/or frayed on the ends? Back the throttle stop screw out a few turns, put the top back on the carb, and check it that it closes all the way. A look at the plug should have been the first thing you looked for, to see if it was running lean.

 

[truckster225]

And when your checking the pedals on the reed valve, look REAL close. Even if its up just a hair, your engine wont operate properly.

 

[Time Bandit]

I checked the reed/petals and intake manifold, no cracks or leaks and the petals are good. but is there supposed to be a hissing noise like that? New gaskets might fix it but I don't want to do more work than is needed. Also I was running 32:1 gas in it but it was smoking blue a lot. The bike calls for 32:1, should I just add more gas and play with the mix.

 

[whenfoxforks-ruled]

Hissing? There is a snake in there! The hissing is probably nothing, just like fooling with the mix ratio. If you are really concerned, pop the top end off and measure/inspect. At least it would cost you a top end gasket set and new rings. Solid piece of mind.

 

[Time Bandit]

Yea but could something as small as too lean or too rich gas really cause that much of an issue? It seems there's something here that's a lot more serious, the bike was not even ride able.

 

[truckster225]

The hissing noise is nothing. Its just the noise you get when there is zero compression. Its just the noise caused by the air moving with minimal friction. There pretty much has to be air getting in somewhere. Im not sure how to exactly pinpoint it. It sounds like you may need to get on google and start some research. I'll do a little reading also, im pretty curious.

 

[truckster225]

Oh, one more thing. Have you pulled the top off the carb, where the throttle cable screws in, and just made sure that the slide is moving smoothly and freely? Maybe just lube it a little with 2-stroke oil. Just to make sure it doesn't get stuck once in a while. THAT was the problem I was trying to remember. My slide looked normal, felt normal, but it would stick once in a while. I rubbed it with a little oil and it cleared my problem right up!

Give that a go!

 

[_JOE_]

The hissing noise is nothing. Its just the noise you get when there is zero compression. Its just the noise caused by the air moving with minimal friction. There pretty much has to be air getting in somewhere. Im not sure how to exactly pinpoint it. It sounds like you may need to get on google and start some research. I'll do a little reading also, im pretty curious.

If there is zero compression the engine wouldn't start. :coocoo:

Start your reading with the first portion of this thread which provides all the information this person needs to find the problem.

 

[Time Bandit]

I'm going to test the slide first and see if the bike starts tomorrow, In the mean time I found that there are a lot of small dents on my top end- does this look acceptable? take a look for yourself -



and here's the cylinder just for the hell of it, looks fine though.

^^that's radiator fluid on the sides not dents.

 

[truckster225]

If there is zero compression the engine wouldn't start. :coocoo:

Start your reading with the first portion of this thread which provides all the information this person needs to find the problem.

Easy there JERK! :blah: Im just trying to help. If YOU would read, it WASSNT running, he was simply hand turning the motor. :yell:

 

[whenfoxforks-ruled]

At some point in the last 13 years, someone lost the big end bearing. I would see about getting the head fixed/modded or replaced. What is the skirt clearance and ring end gap? What is the thrust washer clearance on the big end of the rod? How is the exhaust valve?

 

[Time Bandit]

I lubed the carb, put a new mix in it and started it, the first time it was revving high and then i turned the throttle a little bit and it went uncontrollably high so i had to kill it. After that when I started it, it ran great every time, and I could actually adjust the idol correctly without the bike dieing. I'm not sure what it was but thanks for the help, its running great now.