1980 650 LTD Backfiring...

At low throttle and idle my bike backfires, a LOT. It sounds like a pistol. I'm afraid to ride in certain areas, especially Cincy!!

Doesn't matter if you're sitting still at idle or riding down the road. Speed doesn't seem to be a factor. I haven't noticed it at over half-throttle, but don't spend a lot of time at over half-throttle. The question is, could a small hole, about the size of a dime in the exhaust crossover pipe (factory exhaust) cause the backfiring? As far as we know, everything else is JUST RIGHT on this bike. I don't really want to call a bunch of attention to myself since I'm a new rider. It also has a really rough idle.

Does anybody think this could be a timing issue or maybe a lean/rich condition, or combination of everything. The bike runs extremely strong, just backfires. Is it related to the emissions control stuff?

Thanks,
Abbie

Yes, the small hole will allow fresh air into the exhaust system promoting more combustion. Also, if your smog valve is bad on top of the valve cover is bad it will do the same, actually I think that it causes more problems than not. Most of us remove it and run a hose from one tube to another and cap off the vacuum lines. It is designed to introduce air into the exhaust system. Also of course, make sure timing, air screw, etc are adjusted properly.

I doubt a hole in the exhaust crossover would cause explosive backfiring. This type issue is normally cold air CLOSE to the combustion chamber getting leaked in. It will not normally be a carburetor issue as in air/fuel mixture but could well be that the carburetors are poorly seated or loose in the carb holders or air is leaking in via the smog system... the rubber hoses or vacuum caps that can be cracked or even the carb holders leaking air. Could also be the crush gaskets on your exhaust system leaking air if they were re-used when you took your exhaust system off.

The smog system, as has been pointed out, tends to cause as many problems as it solves if not maintained. There are two hoses going from carbs 1 and 4 and these meet in a tee. The tee goes into another vacuum hose which ends up controlling the vacuum cannister that opens your reed valves. ANY air getting in these hoses via a crack can cause explosive backfiring. This is also true of the vacuum hose going to your petcock. The other carb will have a vacuum cap on it to prevent air from leaking in. Maintenance of the smog system mostly means checking it for air leaks via cracks or missing parts.