#8: Re: Front cylinder does not fire below
3000 Author: eaglebeak, _files/icon_minipost.gif "Post") Posted: Fri Aug 13, 2010
12:37 am
My thoughts are centered
around you pulling the front plug and it was wet and smelled of gas - but
spark plug is firing and it will light up for a little while with starting
spray.
That sounds like you're flooding the front cylinder at idle
and low RPM. Flooding on the low end would wet the plug, keep the cylinder
from firing, and cause some occasional popping or backfiring when rich mix
lit up in the hot exhaust system. Starting spray is volatile enough to
fire even a very rich fuel mix.
Since you have vacuum operated
carbs, I would suspect either a leaking needle-valve/seat assembly in the
front carb or a float setting too high. Either one would cause mild
flooding on the low end that was enough to keep the cylinder from firing
and wet the plug as a result; but as engine RPM increases, there's
considerably higher airflow and fuel demand where the mild leakage
wouldn't be a problem anymore - letting the mixture get more normal and
light-up the cylinder.
Use the clear plastic tubing method in the
picture below to check the float level in the front carb (doing the rear
carb wouldn't hurt anything either). If there's any question about the
level being at the seam of the float bowl as indicated, dropping it 1 or
2mm lower won't hurt anything. If the float level looks good, then I'd
replace the needle-valve assembly - especially if you bought a "bargan"
aftermarket set.
As 1986XV700 mentioned, going though the proper
carb-sync procedure is a must as a FIRST step at 3K RPM, then adjusting
the pilot setting on each carb is the final fine-tune.
Never
assume anything when it comes to a vacuum leak. Since you've had the carbs
off a number of times with old boots to the heads, use the starting spray
(outside on only a warm engine) to spray around the carb boots to check
for vacuum leaks each time you reassemble them since a crack can happen
anytime during disassembly or reassembly.
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