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my INTEK TWIN has minor backfire at idle...what are the possible causes?...the valve clearnces are maybe a little larger than the .005 ...maybe .007.... but I would have thought only valves that are too tight would have caused backfiring...the carb is a fixed jet....not adjustable...but maybe its dirty??...I guess a valve might not be closing properly?..that would do it?..right?...give me some ideas please about possible backfiring causes....thanks!!
 

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I had one of these with a carb so dirty that it had an internal carb port completely blocked, such that it only ran on one cylinder. Also backfired.
I cleaned the carb (tried soaking for weeks in every chemical known to man), eventually found the problem by shining a work light through the ports until I saw the blocked one. Took a piece of wire (I know, not recommended, but it was headed to scrap otherwise), never had another problem, including no more backfiring.
Having said that, I also adjusted the valves at the same time, but found them to still be at mfr spec, so I doubt that mattered. Adjusting these valves is extremely easy, and there's a great youtube video showing how.
Anyway, I would start with cleaning (and rebuilding) the carb, especially if it's been a few years since you've cleaned it. Since you will need to get parts for this, I would also buy the valve cover gaskets and adjust those as well.
Good luck, hope this helps.
Mike
 

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Give it some choke while it's idling, and see if that helps the problem. If it does, one of the idle jet(s) is clogged or dirty.
 

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Backfiring out the exhaust or through the carburetor?
 

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You could pull one plug wire at a time to isolate which cylinder is doing it, if only one is.
 

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Any luck?

Backfiring through the intake can be caused by the exhaust valve not opening, or by the intake valve leaking combustion back into the intake. Early ignition timing could do it, too, as well as a lean condition.
 
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