Since I didn't get a lot of responses to the Idle Drop Problem (paraphrased
here....I have an Idle Drop Problem) I posted yesterday, the progress I made in
solving the puzzle last night might add to the collective (Borg?) knowledge that
makes this list so useful. Actually my so called progress only raises another
question.
I put the Colortune on the engine last night and discovered that the Idle Drop
Problem was being caused by an occasional rich mixture surge from the front
carb. When the engine was warmed up and at idle there was a consistent 100-200
RPM drop on the dwell/tach meter I'd hooked up when the Colortune went briefly
from Bunsen blue (correct mix) to yellow (rich mix). It went back to the
850-900 RPM setting when the Colortune went back to Bunsen blue. It surprised
me that it was a RICH mixture causing the RPM drop off. And here I was looking
for a problem that was making the mixture too lean such as a vacuum leak.
I think that this rich mixture surge is also causing the idle to drop when the
carbs are decelerating, e.g. clutch in, braking for a stop, and I get a RPM drop
(below the 850-900 RPM) that threatens to let the engine die. I bet if I look
closely again tonight I'll briefly see a yellow color on the Colortune after I
rev it up and let it back down, that corresponds to the idle drop.
Now the question is why am I getting a surge of fuel on just that carb?
Could there be some leakage past a needle (float) valve (what do you who have
them think of Grose jets as a replacement?) that's causing the surge? The front
carb has had a little leakage (more like a slight seepage)of fuel past the
o-ring on the plug (even though I replaced it recently) that's in the bottom of
the float chamber cover. I wonder if that could affect the fuel pressure in the
float chamber somehow...although I can conceive of how that would cause a surge
into the mixing chamber.
Could the needle (float) valve be the culprit for both idle drop scenarios?
Advice, comments, confirmations, wild guesses? Any and all appreciated.
TIA
Bud 71TR6 CC57365
71TR6 CC65446
P.S. This was what I sent out yesterday regarding the Idle Drop Problem:
I thought I had cured my idling problem by changing fuel line hoses but I'm
still getting a 200 RPM drop about every 15-20 seconds as the engine idles, it
then it bounces back to the 850-900 RPM setting. I remember some other folks
had this problem awhile back, but I don't recall any solutions. What could be
causing a fluctuation problem such as this. Is there something that would surge
electrically or in the fuel system that would cause it to act like that? It's a
cyclic idle drop so I don't think it's a vacuum leak. I've tried to check or
secure every potential vacuum leak that I could think of.
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