Ok heres my problem: there seems to be no ported vaccum source on my carburator. There are only 2 hookups, one large one for the pcv valve on the front of the carb base and a smaller one on the front of the carb body on the drivers side. I assumed the smaller one was the hookup for the vac advance, but it provides manifold vaccum, thus when the vac advance is hooked up it runs at max advance all the time. This makes for hard starting and poor idle quality. When advance isn't connected it stumbles off the line. There are no other hookups on the carb except a small tube about an inch or so long that sticks out by the heat choke linkage on the pass side. There seems to be no vaccum being drawn from this tube at any throttle position, so i am not sure of its function. Can someone help me out here? Is there something wrong with the carb vaccum sources, or is there supposed to be another source somewhere? Help me please, Marcus
I'm going to watch this thread too. I just set my timing and after reconnecting the advance I noticed that it did not change. The picture is where it was when I got the car. If I switch to the other vacume source (the unplugged hose in the picture) I see the advance change @ idle. I guess my question is the same. Is it correct where it is or do I swap it so it gets full vacume and it advances as soon as the car starts? o No:
Hey Marcus, manifold vacuum is recommended for the advance. If you have trouble starting try turning back your initial advance some. Do you have a timing light or a vacuum guage? They'll help you out a lot it getting it to run right. And Glen, I used to believe that ported vacuum, where its 0 at idle, was best since it came from the factory that way. But a lot of people here recommend full manifold vacuum for the distributer since ported was basically a way to help reduce emissions.
Although it is a matter of taste, manifold vacuum IS NOT the factory recommended source for distributor vacuum advance, and should not be needed. Ported vacuum for advance goes back WAY before any emissions testing; it simply should not be needed at idle, unless the car has a MUCH larger than stock cam. The port on the driver's side of the carb is "ported" vacuum, which means that there should be no vacuum at idle. The ports that supply vacuum to this fixture should be above the throttle plates at idle, producing no vacuum. They should only have vacuum when the throttle is open. If there is vacuum at this port, your idle screw set too far in to keep the engine running, and is uncovering these ports. You have another problem in your carb. PS the vacuum port on the pass side by the choke identifies you carb as NOT a Buick carb (unless 67s are WAY different from 68-up Buick carbs) What's the number on the driver's side, embossed in the vertical rib at the back?
Marcus, If you have the original 1967 carburetor, and distributor, there may not be a ported vacuum source. The specifications for the 1967 400 and 430 call for an initial timing of 2 1/2* BTDC. The 67 engine ran full manifold vacuum to the advance cannister. This provided another 14-18*@ 16" of manifold vacuum. The mechanical advance provides 28-32* at 4800 RPM. When you floor the gas, manifold vacuum (as well as ported vacuum) goes towards 0, the vacuum advance drops out, and you are left with 30-34* of advance at 4800 RPM. These were the stock specs in 1967. You can get better performance by bringing in the advance sooner(by 2500 RPM), but you would need to recurve your distributor, by changing the springs that control advance rate. You would also need to limit the vacuum advance to 8-10*. This has been discussed many times on this BB. Try using the search function, and inputting timing advance, vacuum advance, distributor recurving etc. For now, I would set the initial advance to 2-3*, and connect the vacuum advance to the manifold source. The vacuum advance should have no effect on your starting. It won't come in until the engine actually starts. You may have too much initial right now, and that could be giving you problems. Good luck.
Ported vacuum is not such a bad thing. Especially if you are running a hot cam. When I used run the original quadrajet from my '66, the vacuum source on the carb for the timing advance was full manifold vacuum. That caused a problem, because the low vacuum at idle was barely enough to pull in the timing advance. Then when you flipped on the a/c or turned the steering wheel loading down the pump, the vacuum would drop and the timing would retard stalling the motor. I had to use an adjustable advance in order to compensate, and it was never really "right". When I switched to the dual Carters, they have ported vacuum, the factory distributor is set up differently for that reason, that's why the initial timing is 12 deg. instead of 2-1/2. I no longer have low vacuum stalling problems using ported vacuum. Unless you want to go without a vacuum advance, which would kill your gas mileage, you really should use ported vacuum if you have low vacuum at idle from a cam. Just my 2 cents. :bglasses:
Joe, I might be wrong, but I get the impression that this motor is largely stock. Low manifold vacuum shouldn't be a problem. Marcus, Have you installed a cam??
I currently have a TA C-110 cam installed.... The initial timing is set at 8 BTDC so maybe i should back it down a few degrees. The problem is is that when the vaccum advance is connected, the car idles to fast even when the idle is set to its lowest setting. The timing at idle w/ vaccum connected is around 28 BTDC... The distrubutor is an HEI from a later 455 i got at a junkyard.......
I don't know how wild that cam is, but it sounds to me like you need a ported vacuum source. The advanced timing at idle is what is making it run so fast. Another option might be to have the distributor re-curved, perhaps with limited vacuum advance, which might even give you an increase in power. :bglasses:
There you go, that's the problem. Most HEI's have the wrong curve for a Buick motor. They usually have way too much mechanical advance. Do you have a dial back timing light? If so, see if you can figure out how much mechanical advance is in the distributor, and where it's all in at(RPM) If you want your 430 to perform at it's best, you need to recurve it. You want 18-20* in at the crank, at 2500 RPM or less. Then run 12-14* initial for a total of 30-34* Then restrict the vacuum advance to about 8-10*, and run it off manifold vacuum. You can restrict the vacuum cannister by making a block off plate like this. BTW, the TA C110 is a mild cam, 218/224 @ .050, 110 LDA, 1000-5200 power range. You should have plenty of vacuum with this cam.
thanks for the advice larry.... fortuneately i do have a dial back timing light so ill check the mechanical advance to see how much it puts out. I have a couple original 430 points distributors, any way to use the guts of those to configure the advance curve of the newer HEI back to the original specs?
No, I was referring to the description of the carb in the original post: "There are no other hookups on the carb except a small tube about an inch or so long that sticks out by the heat choke linkage on the pass side."
Marcus, No the weights and springs are not compatible. Your best bet, is to take one of those 430 point distributors, and send it to Dave Ray. He can completely rebuild it, and recurve it, and convert it to HEI operation for under 200.00. Or he can convert it to a magnetic pick up designed to fire an MSD or other ignition box. That is what I have. This is Daves website. Contact him for a spec sheet at the e-mail listed. Daves new address is 24 Buffalo Lane, Yearington, NV 89447, 775-463-1821. www.davessmallbodyheis.com
