Michael wrote:
From: SamuelsMA@aol.com
Listers:
Yesterday I noted that my front Zenith-Stromberg carb was running very
rich (making plugs 1-3 get very sooty and misfire) even after balancing
the carbs.
I asked some advice about using the special tool to lean out the
mixture. I had already ordered the mixture adjusting tool from TRF but
it hasn't yet arrived.
Dick, here---You can pick up a long, 1/8 inch T-handled hex key
wrench from Sears, if you don't want to wait for the real deal. It will
work fine if you don't force the adjustment.
However, Dave from TRF was kind enough to spend some time with me on the
phone discussing the problem. He suggested that it made little sense
that the front carb would all of a sudden begin to run rich unless it
was malfunctioning, and that leaning out the mixture was probably an
attempt to compensate for a different problem. He suggested checking
some other things before adjusting the mixture:
What Dave said sounds reasonable, IF this 1-3 plug fouling started
after having run satisfactory for a while. When you said it had "a
cam..." and stuff, I assumed that the engine was trying to be tuned for
the changes.
1. Check the fuel pressure with a gauge to make sure that it was low
enough (1.5-2 psi, if I remember right). If too high, it can make the
front carb run rich compared to the rear. Pump overpressure can occur if
valves in the fuel pump stick or wear out.
1) It would be rare for the stock, mechanical pump to produce more
than two lb. of pressure. If you have an electric pump, it should have a
pressure regulator set to no more than 3 lb. (two lb. is good)
Don't know about the front carb getting more pressure than the back, or
why it ever would.
2. Take the float chamber off the carburetor and see if a float is
cracked and full of fuel. If so, extra fuel can enter the combustion
chamber.
3. With the float chamber removed, remove the metering needle
assembly and look for dirt. If the metering needle gets stuck, it can
let extra fuel into the combustion chamber.
2) 3) It's always good to know/ check these things, in light of the
current richness.
I'm not sure if I got the details right, but it makes sense to me that a
mixture adjustment shouldn't get way off for no reason on only 1
carburetor. Does this make sense to you?
No it shouldn't change on its own, and if you're absolutely sure it
hadn't been moved early on. But, It is easy enough, once you get the
adjusting tool, to "measure" how far the needles are adjusted. By
running the adjusting screw clockwise, you'll turn it to full rich.
Count the turns, or quarter turns, that you make with the wrench. If you
cant turn the screw CW, turn it the other way, just to be sure it isn't
stuck. Then compare this info by doing the same to the carb that is
producing normal plug readings.
You can also take out the air valves and see how far the needle(s)
casings are up inside of them. When you do the "lift the air valve test"
only go up 1/16 inch. Not a quarter inch like some manuals may direct. I
for one am curious as to what you find!
Dick
Thanks.
Michael
'76 Tahiti blue
CF 57044U
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