back firing

[DevonCbx]

I noticed lately thast there is some back firing of the left bank of carbs. I took the plugs out and re-gaped them. There seems to be less back firing now. Number 1 spark plug was way more deteriated then the rest of the plugs. Is this a sign of too rich or too lean? Is there a certain amount of turns on the fuel adjustment screws. If I reseat them lightly, how many turns on each screw when I back them off?

Thanks

Thanks

[alimey4u2]

Regapping plugs reducing backfire ?
Don't forget that they fire on the ignition & the exhaust stroke. Sparks may be quenched on the compression/ignition stroke if everything isn't perfect. On the exhaust stroke it's easier for the plug to fire as the "atmosphere" is not compressed....
Sooo.... If you have imperfect combustion it is easier for the plugs to reignite the remaining unburnt mix during the exhaust stroke, hence the backfire....
So what does that all say ? Basically imperfect combustion due to fuel/air ratios being out or poor ignition being the most obvious but then that is being simplistic...

[steve murdoch icoa #5322]

Duane, from what i have read over the years, back-firing is usually caused by an air leak. It could be an exhaust pipe leak at the port, an airbox leak and since you just had the carbs off it might be the rubber manifolds are not properly seated.
Another cause might be unburnt gas. With the gas leak you have, maybe a stuck float, you could be getting too much gas in your mixture in one or two of the cylinders.
As far as the mixture screws, i started out 2 turns on all the carbs and eventually ended up at around 2-1/2.
These are just ballpark ideas.I am sure the brains of the organization will have some thoughts for you.

[Brian G]

Hi -

Just to confuse the issue...

some back firing of the left bank of carbs

In addition to the advice offered in the previous postings, my understanding is that backfiring through the carbs is often due to an excessively lean mixture - sometimes accompanied by erosion of the plugs. As previously mentioned, backfiring in the exhaust pipe can often be attributed to air leaks at the exhaust pipe/head connection.

If you have recently changed the air/fuel adjustment screws, that would probably be the first place to look . I'd be hard=pressed to explain why back-firing through all 3 carbs on the LHS could be due to an ignition fault, but I was wrong once before....

Hth,
Brian