I'm getting really annoyed with the carbs on my car. It's a 1971 Midget. I
can't get the SUs adjusted right for anything now. Valves have been adjusted
and timing set. But the thing sounds like a model airplane. It idles OK, and
if I sit and rev it that seems pretty good too. But try driving it and it
has almost no power and starts bucking and backfiring like mad, and I have
to have the choke at least partially out to do that.
A little info for anyone who might help diagnose this: I'm pretty sure
everything else is good. When I got the car it had a strange homemade intake
bolted to the original intake and a Carter carb. But it ran, pretty good.
But I wanted SUs on it, so I took the ones from a 1967 (AUD 136), cleaned
them up and rebuilt them, including new throttle shafts, and put those and
the 1967 intake manifold on the car. Ran OK, but not great. Had trouble
getting the idle down. I then discovered the intake had a crack in it, so I
took it all off to put the 1971 intake on it. In the process found that the
arm on the throttle shaft of the rear carb was on in such a way that the
plate couldn't fully close. Fixed that. Both carbs now seem pretty air-tight
with the plates closed - I tried blowing through them while holding the
plates closed and couldn't do it. Reassembled everything with the 1971
intake and 1967 carbs, and thats where I am now. The distributor is in good
shape - had it out and cleaned and inspected it carefully. Put in new
points, condensor, cap, wires (Magnecor), and plugs (NGK). Still old coil,
but it had run well with it before, and in my experience coils usually work
or they don't, though they may be intermittent.
I'm guessing the mixture is still off, as it seems like adjusting the
mixture doesn't do a lot for it. The carbs are balanced correctly (according
to the Carb-Syn) and the idle is right (700 as per Bentley). One thing that
seems strange to me, though. With this adjustment the throttle on the front
carb is open considerably more than the rear, which is almost closed.
One other question - the front carb has a small nipple on it near the base
where it mounts to the intake, pointing toward the front of the car. What
should attach there? Right now it's open. I assume it's a vacuum port, but I
really can't feel any vacuum on it, and covering it doesn't seem to affect
anything, although I believe it goes straight into the throat of the carb. I
have the distributor vacuum advance connected to a port on the intake.
If there is anyone in the Northern VA area who would be willing to come by
and give me a hand, I'd really appreciate it!
Thanks,
Eddie
1971 Midget (going to be named Wheezy if it keeps this up!)
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