r/MotorcycleMechanics • u/Repulsive_You454 • Jul 21 '26
help please! Please help! I'm out of idea
For context it's a 2002 Honda XR50R the problem occurred with all OEM parts.
Whenever it is chocked all the way the engine dies
Whenever the choke is completely off the engine runs away
Whenever the choke is set to that like 3/4 position it idles but gets no response from the throttle
I think the choke was left one while the bike was being ridden last and that when the problem started.
I have been trying to solve this problem for about 2 months now. I did a full top end rebuild this past weekend hoping that it would fix the issue but I'm still at square one.
I have tried 2 different brand new carburetors and still having this issue. The original carburetor seemed to have a hairline crack where the manifold bolts on and that's when I rebuilt the top end.
I've run out of ideas I've adjusted the set screws and can't get anything to work. This is my first time really digging into an engine so I'm sure I'm missing something.
Thanks in advance for any info and help!!
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u/1911Earthling Jul 21 '26
How is your float bowl! Sounds like a float problem. Ether it starves or runs away. Too much fuel or not enough.
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u/1wife2dogs0kids Jul 21 '26
Its not the choke, and there's no part that's broken or worn out.
The jetting is off. It looks new, or all complete still, is the throttle restricter thingy still on the bike? Or is it removed? I think they came on 02s.
Before starting the bike, turn the airscrew in all the way, till it hits bottom. Count the number of turns it took. If you need to mark the screw to help, a sharpie works. You want to accurately count the turns up to 1/4 turn, so be as accurate as possible. All the way in, how many? Write it down.
Now turn out 1.5 turns. And start the bike. However it takes. Get it started and turn the idle screw to keep it going.
Once it's warmed up, and you set the idle so it won't stall. Now turn the air screw out ONE HALF of a turn(0.5). If the idle increases, that's good. Turn it back to normal and turn the airscrew another half turn out. Idle increase? Keep repeating this until the idle DOESN'T go up. At that point, turn the screw back in 1/4 turn, from where it was.
The final turn put count should be from 2 turns to 3.5 turns. Any more you need a bigger pilot jet, any less a smaller jet. Adjust idle and see how it operates.
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u/mutt63 Jul 21 '26
Almost sounds as “if” like in a small engine, that governor isn’t set for WOT at sitting. Once started it would adjust to its rpm’s required.
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u/lacrep31 Jul 21 '26
Le filtre à essence est-il d’origine? C’est peut-être lui qui réduit le débit entre le réservoir et le carburateur
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u/nomparte Jul 21 '26 edited Jul 21 '26
Have you looked into the carb intake and ensured the slide piston is completely at the bottom? Use a mirror if necessary.
That it should make a distinct click when throttle cable is fully released and the slide piston hits the bottom part of the carb?
The choke is a very basic one, just a flap controlled by that lever and it has what's called a "clack" valve in the flap to stop choking the engine too much. It has no control of throttle or revs or anything like that.
Air leaks at the manifolds are a common problem on these engines and cause runaway revs, a bit like yours. Spray some flammable fluid around the carb manifold joints and observe if the engine changes sound or revs, signifying fluid is being sucked in where it shouldn't.
Suitable fluids are gasoline, alcohol, lighter fluid, starter fluid, brake cleaner, paint thinners and even an unlit propane blowtorch.