Light, occassional backfire at cruise

[Azgunner]

Just wondering if others have this same experience or know what causes it. I'll be at a steady hiway cruise, 70-80 mph or so, & out of the blue I'll get what sounds to me like a rata-tat split second of a backfire out the pipes. This may or may not happen again for another 100 miles or more. this has happened with the motor as a 95" & 44cv carb & as a 117" with a 45 Mik carb.

Is this just one of those ideosyncracies with carb'd bikes?

[harleytoprock]

Sounds like a lean condition. Does it happen more when the air temperature is cool?

[rbabos]

Could be a sparkplug going for a dump.
Ron

[Azgunner]

It's done this every now & then over tens of thousands of miles & 2 builds.
Not temp related either. It may backfire once & then not do it again for a few hundred miles.

I'm not too worried about it, just wondering how normal or abnormal this is.

[bigfoot5x]

I don't think I would say it is normal but it doesn't sound like a real problem unless it gets worse. Then again if it gets worse maybe it would get to a point where you can figure out what causes it! The standard answer is lean condition. You changed the carbs and it still does it. Maybe a slight leak somewhere in the exhaust or at the intake gaskets. Again, these are standard answers and places to look.

[Barrett]

My brother had a bike that did the same and it was a bad plug wire.

[rbabos]

It's done this every now & then over tens of thousands of miles & 2 builds.
Not temp related either. It may backfire once & then not do it again for a few hundred miles.

I'm not too worried about it, just wondering how normal or abnormal this is.

Well that would rule out a sticking valve. I'd be looking at what parts were used in both builds, particularly in the whole ignition circuit. Don't think in this case lean is the culprit. It would happen a lot more frequently than every few hundred. I'm thinking out the pipe backfire is caused from an ignition interupt somehow, or possibly an injector or wire to injector is faulty in some way base on it happening in a steady state of cruise.
Ron

[Azgunner]

Thanks for the replies. It is kind of a wierd thing. Seems to be no good reason for it that is apparent. May be something going on with the DTT ignition. Plug wires have been swapped back & forth a couple times does it with stock wire & Magnecor wires.