I get the occasional backfire when disengaging the clutch and coasting up to a stoplight. This is most often a single bang, not a gumble pop, pop, pop. This occurs mostly afterI have downshifted or run a gear up toward the shift point and let off the throttle or clutch (maneuvering in traffic).

A friend, who works on engines, has told me that this can damage my engine. Supposition: the exhaust valve may be slightly open and burn because of the excess fuel ignition in the hot pipe. True or false or maybe?

From what I have read on this forum, CCW makes the engine richer. True or false ?... no maybe. Note: limited carb experience.  Supposition: the screw being turned MAY meter an air passage. If so, backing it out would permit more air and thus a leaner burn. Second Supposition: the screw being backed out is a fuel flow needle valve, thus backing it out would permit more fuel and a richer burn. Which is it?

If I am enjoying two or three backfires in a 20-minute commute to work, should I rush straightaway to get help resetting the carb, or should I consider resetting it when I get a roundtuit?

Roger that. Turn out ... richer mixture. From my limited experience, I would probably find manufacturer specs ... turn in all the way ... turn out to manufacturer specs and then maybe a quarter turn out from there. Right?

Now, regarding the urgency of all this. I much prefer riding the bike than screwing with it (pun intended). I am getting more backfiring now that I use 87 fuel ... maybe two or three in a 20 minute ride. Should I restrict my riding until I get this at least mitigated (thumper will always clear her throat), or is this one of those round tuit things?

'round to it type thang, I suspect.


As far as "burning your valves" because of backfiring --

let's see, mmmm  Let's think about it a bit.

Exhaust gas is naturally glowing burning hot already and exhaust valves normally glow dull red in normal use.  

A common EPA trick from the '80 and so on is to dump fresh air into the exhaust manifold just down from the valves to help combust the excessively high hydrocarbon content of unmodified exhaust gases.  

If something was gonna "burn a valve" that would do her, don't 'cha think?  It doesn't ....



Backfiring and popping

A pulse of hot hydrocarbon rich stuff winds down the header pipe and hits the muffler chambers, finds some free O2 hanging around down there and has a party.  What does that have to do with the situation way upstream at the valves?

If you want to burn a valve, let your exhaust valve clearance get way too tight so the exhaust valves don't close all the way -- that'll do her !!