Eddie,
There's a lot to narrowing down the problem by long distance, but to answer
two of your questions:
1. the small nipple is a vacuum advance connection to the distributor.
2. if you're seeing one piston riding higher than the other, then your
butterflies are not set properly. To correct this problem:
You must make sure that both idle screws are backed out and not making
contact with the linkage on either side. Next loosen the linkage clamps on
both sides and hold the butterflies closed. Set each pin on the linkage so
it just makes light contact with the lost motion lever (forked lever) on
each carb. Making sure both are exactly the same, tighten the clamps.
Rotate the linkage by hand and observe if both pins make contact
simultaneously with the movement of each butterfly. Do this by watching the
contact point on each last motion lever. If they make contact at different
moments, repeat the previous process until they are identical. Once you
have acheived this, turn in both idle mixture screws one turn from the
point that they just begin to operate the butterfly. Again, you want the
linkage to make contact simultaneously on each side. Start the car and
adjust each screw the SAME amount until you have the proper idle. If you've
done everything correctly. you should be able to observe both pistons
rising the same amount when you open the throttle. Continue to adjust both
screws until the move in unison (one more, one less to maintian correct
idle). If you have made certain that both jets are turned out an equal
number of flats from the their start position, slightly the front piston
approx 1/32 inch and see if the idle increases or decreases.
increase = too rich
decrease = too lean
slight momentary increase = correct.
repeat with rear carb.
Observe that the height of each piston when running is the same at idle and
when opening the throttle. If they idle the same but are not in sync when
you open the throttle, then the amount of oil in the dashpots is uneven.
Also listen for differences in pitch with regard to the airflow.
Other things to check are float levels (both the same) and making sure the
jets are centered. If you missed to first step, balancing butterflies,
you'll never get it sync-ed right.
Gerard
>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!)
--
Please visit Four Points Travel -
Discount Online International Travel Reservations
http://www.gerardsgarage.com/fourpoints
To make a reservation please call Toll Free 1-800-272-3253
G G Gerard Chateauvieux
E A
R R pixelsmith@gerardsgarage.com
A A
R G Pixelsmith on Duty
D E
S http://www.gerardsgarage.com
|