Jump to content

HELP Bike Revving itself????

By JoeMX82,
in General Dirt Bike Discussion

 Share

Recommended Posts

Explorer

JoeMX82

Posted
Posted

I am new to this forum and have used the search feature, but I have not found the answer to this particular issue. I have a 05 YZ 250 and just recently it has started revving itself all the way to " red line" when I am not doing anything. This started once I returned from my local track and washed the bike, I am always careful not to get water in the motor and only use a garden hose. What happed is I started the bike on the stand and after about a minute it just revved itself up like I pined the throttle open! It seemed as though when I gave it extra gas that it would correct the problem, but it did this a couple of times.

I then took the bike to the track the next weekend and again had this problem. It does seem as though I only get this in the pit area when the bike is somewhat cold and it has not happened on the track, but I am really nervous!! At the track this only happend when I was in gear with the clutch in but at my house on the stand it occured in netural with me no where near the bike??? Also, one last thing is that after ridding a few laps I would leave the bike to idle on the stand hot and the revving did not occur.

What could be causing this? I have checked my compression which is great ( about 160-165), I have put in fresh gas also...Any help would be greatly appreciated!!!:thinking:

Link to comment
Share on other sites
Grand Master

Charlie755

Posted
Posted
I am new to this forum and have used the search feature, but I have not found the answer to this particular issue. I have a 05 YZ 250 and just recently it has started revving itself all the way to " red line" when I am not doing anything. This started once I returned from my local track and washed the bike, I am always careful not to get water in the motor and only use a garden hose. What happed is I started the bike on the stand and after about a minute it just revved itself up like I pined the throttle open! It seemed as though when I gave it extra gas that it would correct the problem, but it did this a couple of times.

I then took the bike to the track the next weekend and again had this problem. It does seem as though I only get this in the pit area when the bike is somewhat cold and it has not happened on the track, but I am really nervous!! At the track this only happend when I was in gear with the clutch in but at my house on the stand it occured in netural with me no where near the bike??? Also, one last thing is that after ridding a few laps I would leave the bike to idle on the stand hot and the revving did not occur.

What could be causing this? I have checked my compression which is great ( about 160-165), I have put in fresh gas also...Any help would be greatly appreciated!!!?

Repost this in the Yamaha 2-stroke 250 section. You might get better responses there. Good luck to you. :thinking:

Link to comment
Share on other sites
Veteran

MXSteve89

Posted
Posted

First check the obvious things...cable operates smoothly, no debris in the carb, no air leaks, etc.

If you must, take the carb apart and clean it out really good. Make sure the slide isn't sticking, and that it operates smoothly. Check the action on the cable, and lube it up really good. No binding or anything like that. Then check the carb boots, Mainly, the boot that goes from the carb to the reeds. If there is an air leak, that would be where it has to be in order to cause the revving.

Good Luck, and report back!! :thinking:

Steve

Link to comment
Share on other sites
Enthusiast

ARyder

Posted
Posted

I chased this same problem on my 250R quad for 6 months. Turned out the needle in the slide wasn't going back down and hanging the throttle open. When it happened one too many times on the track I changed carbs and found that the slide was actually a for a 36mm carb and I was running a 39.

Anyway, your needle may have enough play in it to hang open. Just a thought........

Link to comment
Share on other sites
Explorer

JoeMX82

Posted
  • Author
Posted

wow thanks for all the quick replys, just some additional info...When I say cold I mean south texas cold and the bike was not on the choke. Also I don't think it is the cable as it feels smooth and also happens when I have not revved the bike and also am not touching the throtte.

Question: Could it be a vacume leak if it is only doing the revving cold and not all the time? Sorry for all the detail but I am fairly new to this and just want to have a better understanding. Also, how would I know if I had a leak, could I see it obviously or is this something that I need to test for somehow.

Again I really appreciate the advice.. and I plan to spend tomorrow working on this issue as I have the day off work

Link to comment
Share on other sites
Veteran

MXSteve89

Posted
Posted

Honestly, I doubt it's an air leak. Otherwise, it would be more constant. Pull the carb and check the slide out. Like I mentioned in my first post, chances are your problem lays in there. It could be sticking, there could be debris in the carb, who knows?

Until you pull it though and check it out THOROUGHLY, it's all guess work and no one will be able to give you a solid answer. :thinking:

Link to comment
Share on other sites
Veteran

MTO

Posted
Posted

It sounds like a lean condition. Like it's starving for fuel. If you forget to turn the gas on and the float bowl starts running dry, float level could be too low, could be an air leak...

In an extremely lean condition 2strokes will often times just start revving real high.

Link to comment
Share on other sites
Grand Master

OLHILLBILLY

Posted
Posted

If it idles back down after you "give it a little gas", it sounds like a carburater or vacuum leak problem. Something you can try. Take the bike OUTSIDE, put it on your stand, start it, and while it's cold spray a small amount of starting ether on and around the motor side intake boot. If the motor revs up any, where ever you were spraying the starting fluid is your vacuum leak. If no change, move on to the carburater.

And also, 160-165lbs of compression is just marginal, for a good top end you should be seeing 190-210lbs. Be ready to put a piston in it before too long.

Link to comment
Share on other sites
Grand Master

sonobob

Posted
Posted
It sounds like a lean condition. Like it's starving for fuel. If you forget to turn the gas on and the float bowl starts running dry, float level could be too low, could be an air leak...

In an extremely lean condition 2strokes will often times just start revving real high.

I'm thinking MTO is on the right track. I've seen two-strokes do this as they are running out of fuel. The last remaining bit of gas dwindles, increasing the ratio of air in the mix, making a very lean mixture and sending the engine revving to the moon before dying.

If you know for certain that the fuel tank wasn't emptying when you experienced all of these situations, then the fuel system would be the next place I would begin looking. Like others said, check everything in the carb-including the float levels and the potential for a sticking float; check your carb vent lines, inspect the fuel filter that's in the petcock on the gas tank, inspect the fuel supply lines. From their, as other's have mentioned also; check the intake boot, the reeds and reed block and the seal around that; and if it already hasn't been mentioned, I'd check the crank seals. A worn and leaking crankcase seal can create a lean condition.

Good luck, keep us posted.:thinking:

Link to comment
Share on other sites
Explorer

JoeMX82

Posted
  • Author
Posted

Update: I started the bike cold and sprayed starting fluid all over the carb boot, cylinder head, crankcase seal, and everywhere else I could and no change in revs. Next I am going to clean out the carb and check the slide (not sure what that is, but hoping it will make sense when I see it) lol, any advice is welcome, and this forum has been a huge help! Thanks!!!

Also The bike had plently of gas every time this revving occured.

Link to comment
Share on other sites
Grand Master

sonobob

Posted
Posted
Update: I started the bike cold and sprayed starting fluid all over the carb boot, cylinder head, crankcase seal, and everywhere else I could and no change in revs. Next I am going to clean out the carb and check the slide (not sure what that is, but hoping it will make sense when I see it) lol, any advice is welcome, and this forum has been a huge help! Thanks!!!

Also The bike had plently of gas every time this revving occured.

The slide is the machined "piston-like" part inside the top of the carb that is attached to the end of the throttle cable and slides up and down, adjusting the amount of air flowing through the carb and into the engine, which also regulates the amount of fuel drawn into the mixture. The needle jet is installed through the opening in the bottom of the slide and extends out the bottom. The sides of the slide should be formed with a shape that should allow it to be reinstalled into the carb in only one direction, but I have heard stories of slides being reinstalled backwards, or 180 degrees out of proper alignment, so check that before removing the slide to help avoid any potential problems when putting everything back together.

You mentioned that you had sprayed the crankcase seal. I don't mean to sound like I'm being rude, but just to make certain; you did pull the ignition cover and spray behind the flywheel, right?

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing
×
×
  • Create New...
Terms of Use
Copyright
Privacy Policy