Topic: Help troubleshooting backfire

[mossen]

Hi everyone

I have a 78 CB550K, and it has a small backfire. Its not loud, it sounds like it is just spitting every so often. It is only on the right side, and it seems to be coming only from the #3 pipe. It is more frequent and a little louder after the engine is warm. It mostly occurs at idle, and never happens during 1/2 or more throttle.

I measured the float level using the clear tube test today, the #3 level was 1-2 mm higher than the others. Could something as simple as that cause this to happen? Any other suggestions of what I could check for? Valves adjusted, timing set, and points set less than 50 miles ago.

Thanks!
mossen

[scottly]

I measured the float level using the clear tube test today, the #3 level was 1-2 mm higher than the others. Could something as simple as that cause this to happen?
mossen

Yes, possibly.

[Popwood]

Suggest you adjust your pilot air screw (slow jet circuit) and lean it a bit. The popping can be from too rich a fuel mix. But it could also be from air leak in exhaust. Be sure your header is tight where it joins the exhaust cylinder port. Those would be the easy things to check first.

[TwoTired]

I measured the float level using the clear tube test today, the #3 level was 1-2 mm higher than the others. Could something as simple as that cause this to happen?

Yes,  My 78 did the same thing until I got the floats and float valves sorted and working properly.

However, spitting back through the carbs can also be a carb sync issue.

Cheers,

P.S.  Some people call a backfire a pop out the exhaust.  Best to specify in the question.