Engine is over revving when I release the throttle. Help!

S

StrontiumEthics

New Member
My engine was working just fine last week. Then I havent rode it in one week. I made sure the petcock was closed, and choke was close before I leave my bike out for long period of time. Now today im riding it and it takes longer to start (Pullstart), and when I give it full throttle, and release it it just keep reving. When I release the throttle I keeps reving REALLY high, then a couple seconds later the RPM's go down. I thought it might be carb so I adjusted the idle screw. Still didnt change anything. Then I replaced the carb, and still didnt change anything. I am at wits end! What do I do now? It just keeps overreving, but it does idle but after a while it RPM's increase. What DO it do!
 
Sounds like an air (vacuum) leak to me. Check your intake manifold gasket first then where the carburetor attaches to the manifold. There are other places to check but start there. The crankshaft seals can also give you problems. Remove the magneto cover and look for oily residue inside the cover. That would indicate a bad seal behind the magnetor rotor (magnet). Are you sure the throttle cable isn't binding? Look down the throat of the carb and check that the barrel (slide) is moving freely and returning to the idle position when you release the twist grip. Check these things and get back to us with what you find.
Tom
 
I did check change the intake gasket I also thought there was a leak. It turns out that was not the problem either. The crankcase leak sounds very interesting, I dont believe i heard of it before. Can you elaborate on what exact goes on in that problem? Im gonna check first thing tommorow for it. I had the engine for about 750 miles sofar and it hasnt given me that much problems. Its a little strange because all I did was leave it outside for like 1 week and when I get back its acting all wierd. I am perplexed. Does it have a period or something?
 
Its so strange because when I release the throttle it just goes back into place, I also tryed usng the throttle cable on other bike. I also adjusted the throttle wire tension barrel thing and put it all the way down (least tightest). The bike Also Idles but it doesnt when I give it like full throttle and release it RPM's jump.
 
There are two crankshaft seals. One is on the right, behind the small primary gear, the other on the left behind the magneto rotor, or magnet. If either are bad the engine will draw in air around the seal causing the same problems as an intake manifold/carb leak. Oil residue in either the mag cover or the clutch cover is a good indication of a bad crank seal. They are replaceable and available at PistonBikes, ( http://www.pistonbikes.com/category-s/10.htm ) one of our sponsors here. A bad crank seal is not a very common thing but it does occure and can give you fits and a poor running engine. The most common is the one on the magneto side due to the incorrect assembly at the factory. They sometimes do not drive the seal in completely and the rotating magnet rubs it and causes it to fail.
Tom
 
Hmmm.. Very interesting. I dont believe that is the problem because this problem just happened over a weeks period, and the bike wasnt even running. But It is DEFINATLY worth looking for. After all the problems are the most wierd things 90% of the time. Thanks Will check for it tommorow. But can you brew up any other possibilies?
 
Ok I opened up the mag and there was NO black oil, I also changed the carb barrel and the overeving went down by far! But now there is NO POWER or TORQUE, engine feels like its like starving. There is a black slug kinda thing on the engine block below the carb. I never really payed attention to it. Sofar no other head gasket seems to be leaking. In the end, the engine didnt start again. Ahhhhhh. What can I do at this point! Anyone had any ideas?
 
have you tried changing out the intake gasket? you might try that. Its easy to make a new gasket
you can get gasket material at most auto parts stores. Also get some high temp silicone gasket sealant in what ever color you like. Smear a very thin coat of silicone on each side of the new gasket then install the gasket. While your doing that you can also smear a light coat of the silicone on the carb to intake area. Look at some of my stickys on installing the carb you will be able to see how to do it. do not over tighten the top of the carb either hand tight is enough over tightening the carbs cap will cause the throttle slide to stick or bind making for a crappy throttle response.
Norman
 
Ok Well. First problem. When I disassembled the carb I noticed something quiet strange. THERE WAS FUEL INSIDE THE FUEL BOWL. So there was fuel actually slushing around inside the fuelbowl! Not everything began to make sense. the float wouldnt rise and the carb would overflow and feed to much fuel! Once i changed the fuelbowl It ran like before except a little slower but I think its because of the fuel I mixed. And Occationally the same thing happened with the throttle but I think that is because the throttle slide gets stuck. I have to check that out some other time. I only got about 2 hours to play with it today. Any comments?Suggestions? Sofar. I am having the same prob but its not as reoccuring as the last time. It happens ONLY sometimes.
 
I tried replacing the intake gasket! and the same thing still happened. Guys I am back to square one. The same thing is happening. Its not the slide because I thoroughly check its multiply times today. Its not the carb I tried 2 different ones. Its not the seal by the mag, and its not the intake gasket. I'm going crazy Here!!

So these are the things I checked Please help me add to it

1. Intake Gasket
2. Carburator (Disassembled it)
3. Seal by Magneto
4. Carburator Barrel Slide
5. Throttle Cable

Tomorrow I am gonna check the space where the Carburetor and Manifold connect. After that I will be totally lost. Im about to just buy another engine!
 
take a can of carb cleaner or even wd-40 spray around the cylinder base gasket, around the split seam on the engine, and starting at the carb spray around the carb to intake manifold seam and at the intake manifold to cylinder. spray it on kind of heavy do this while the engine is idling set the idle a little fast. While spraying the thing if you have a leak in the engine it will do one of 2 things either speed up or even slow down and it might die if the leak is large.
Keep the spray away from the air cleaner as it will either seed up or die if it gets a shot in the intake of the carb.
Heck spray a shot at the air cleaner intake so you can see how it will react.
Then you can go on a leak hunt on the engine.
If your engine is painted use wd-40 carb cleaner will eat the paint off of the engine.
Water will also work but not quite as well, it might be hard to restart if you use water.
Norman
 
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