Motorcycle popping on acceleration

Question

I have a 1975 Honda XL250 that I bought earlier this summer. Up until recently its been running great. It was leaking a little gas, but nothing too serious. When it started to get worse, I opened up the carb and cleaned it out. I figured the float needle wasn't seating properly. This largely solved my problem, although there is still a little bit of drippage. I need to get a carb kit and just haven't gotten around to it. So the cleaning of the carb took place on Monday. It wasn't starting, so being a relative noob, I thought it might have something to do with the carb flooding. After cleaning it I tried to start it again, but still no dice. Tested the spark, and it was sparking fine. Not really able to think of anything else I did some research and came across a post that said sometimes you may get spark on a test, but when it's back in the chamber it won't spark due to pressure or something along those lines. So I figured, my spark plug is dirty anyway, a new one will cost me $2, and at the very worst I have a new plug. Anyway, this ended up solving the problem. It started right up.

Since then, I rode it to class yesterday and just cruised around town later at night. It was working fine, but then when I was cruising I noticed I was losing some power on acceleration. It was sputtering if I accelerated hard and would make some popping noises. Not loud ones, but popping nonetheless. The idle wasn't very smooth this morning when I rode it to work and it actually died pulling up to the first light.

Does anyone have any suggestions for troubleshooting or fixing this?

UPDATE: I set the idle a little higher and that seemed to help, but when I rode it back to work it was still giving me problems. I stopped off at the gas station to fill up, despite still having what I thought to be enough gas in the tank. Anyway, I filled up and now it idles and runs fine.

UPDATED UPDATE: So after getting home from work it sat for a bit and now I'm having very similar issues. Sometimes when I accelerate from a stop it will sputter and either come very close to dying, or just die. This is definitely not due to me shifting improperly. There's a lot of popping when I just rev it, and sometimes it has trouble idling.

Answer 1

I need to get a carb kit and just haven't gotten around to it.

A carb kit for a 1975 Honda may be harder to find than you think. You'd better start searching for that now or maybe even a used carburetor, if you can find one.

My guess is the obvious one: Something did not seal when you worked on your carburetor.

Pull it apart again. You missed something, and it could be something very tiny like Over/Under tightening some part or getting gasket material in the way or not in the right spot.

If you know (or can find) anyone who is good at rebuilding carbs, it would be a big plus to get with them.

Answer 2

If by "spark plug was dirty" you mean "black and sooty" then you're running rich and need to either lean out your mixture or double-check your air cleaner and make sure it's good. I know my old 73 CL125 would occasionally accumulate an impressive amount of dead leaves and pine needles around the screen of the air filter. Only took a few seconds to pop off the side panel and brush them off, and made a noticeable difference in sound and power (such as it was).

Answer 3

Background

This is a lean condition if it is popping and backfiring through the exhaust.

Conclusion

Based upon the data you've given thus far I would remove the float bowl and blast out all of the jets, in particular your pilot jet. Get a small piece of copper wire that will fit through the jet and make sure you don't have blockage. This is common. The XL fuel filter in the gas tank is garbage and very small particles get through it. Depending on year, there was recall. Put an inline fuel filter between the fuel tank and the carb in fuel line, just cuz.

Perform the same as above with the main jet.

Use the carburetor cleaner to blast out the air and fuel gallies in the carburetor body.

Validate that your intake manifold (rubber) is soft and pliable. If it's hard and cracked you could have an air leak at the manifold. Symptoms would be high idle that falls slowly to normal.

Remove the small aluminum plug at the top of the carburetor between the manifold boot and the top of the carburetor. You find an air screw there. Adjust the air screw a half turn in and test. Wash repeat this until the popping goes away. This is last, after you ensure your lean condition is not caused by the other issues. It might seem counter-intuitive but checking your previous work seems more important and that's how I would approach it. Either way, get access to that and adjust as necessary.

Hope this is helpful.