I have a 1980 carb and need to know which ports to use for brake booster, PCV and vacuum advance. I was going to connect booster to 1 , PCV to 5 --- correct ? Which port for vacuum please.
Thanks Redman. I should have been more specific in my question " Which port for vacuum " , I meant vacuum advance , so you answered my question.
Port #1 is FULL manifold vacuum for power brakes. Port #2 is FULL manifold vacuum often used for the secondary choke pull-off. Port #3 is fresh air supply (filtered) to the hot air choke tube going to the intake manifold. Port #4 is FULL manifold vacuum, good source on that carb for the transmission vacuum modulator. Port #5 is FULL manifold vacuum for PCV. Port #6 is most often the for the distributor vacuum advance. Most Q-jets post 1967 have PORTED vacuum at that location but many Buick Q-jets are FULL manifold vacuum. .......hope this helps some.....
The power brake booster and transmission vacuum modulator both are connected to intake manifold fittings, NOT to the carburetor.
Correct Larry, some factory and aftermarket intake manifolds have provisions for full manifold vacuum which can be used for power brakes and the transmission vacuum modulator. Even so be aware that the intake manifold can NOT be used for PCV as I often seen done on vehicles brought here because PCV REQUIRES even distribution to all 8 cylinders or you'll be sooting up the ones on the runner(s) where it is attached........
Just talking about the Buick V8s. Not sure why anyone would complicate things by looking to run the power brakes or modulator off the carburetor. Easy enough to run the PCV off the the front nipple intended for that purpose. I missed that he was asking what to run the PCV off.
Larry, keep in mind that a high percentage of the population ditches the factory intakes and have to often use vacuum ports on the carb to have enough or the correct ones. If using factory intakes, or aftermarket intakes that offer the correct locations for vacuum ports that is what I would do vs running all the hoses up to the carburetor......
Yes, then you really have no choice. I'm just talking about Buick engines here. All the aftermarket intakes from Edelbrock and TA have the same threaded bosses in the same locations as the stock intake. Not sure about the Offy intakes. Have you ran into that issue with the aftermarket Pontiac intakes?
Most of the dual plane units are tapped with vacuum ports but lack the correct port for the factory PCV supply that feeds from both plenums. Single plane intakes come up short for most makes and models. It is always best to supply PCV from the carb baseplate as they are split for even distribution to all 8 cylinders. For power brakes doesn't much matter as it's just using it for reference, same as the distributors VA......
How about this TA SP1 port on the back of the plenum. Good or Bad? That is what I have been using with the QJ since bolting on the SP1 15 years ago. Nice short direct connection to the PCV valve at the back of the intake. My AED 1000 Has a nipple in the baseplate.
It would work fine for PCV provided if it feeds all eight cylinders. Most single plane intake have at least one provision leading into a common plenum area. It's the dual plane intakes that often come up short. PCV is constant flow and needs to be evenly distributed to both sides of the V-8 engine. ALL other ports below the throttle plates are manifold vacuum and can be used as reference for power brakes, distributor VA signal, etc. EGR is ported and the supply source will be found in later model carburetors, but the factory used a "high" source location and/or a bleed-off slot to kill some of the signal for EGR operation. Ported vacuum designed for the Vacuum Advance has a precisely located source so it is FULL manifold vacuum right off idle. Folks often use the WRONG location when trying to hook up their VA to ported vacuum therefor get poor results. If your engine doesn't need a butt-ton of timing at idle, and you are using ported vacuum for the VA, it simply has to be hooked up to a port designed for it. At that point the only difference between manifold vacuum and ported vacuum for the VA is that yo have no added timing at idle and coasting using ported vacuum. Many q-jets post 1967 have a very well located ported source to run to the distributor. They use a vertical cut "slot" which is uncovered with the slightest movement of the throttle right off idle.......
Another question please. This carb has a hot air choke that I want to convert to electric. Does this diaphram have anything to do with the choke set up ? Do I keep it.
The choke pull-off has two functions. It unloads the choke on a cold start and keeps the secondaries from whipping open and causing a momentary lean condition (stumble/hesitation/bog) going quickly to full throttle. The conversion is easy, block the vacuum supply to the housing, discard the gasket and install the electric choke element. Here is one that is USA made, lifetime warranty and comes with a pigtail for the wiring harness, hardware, instructions, etc.... https://cliffshighperformance.com/product/electric-choke-and-pigtail-connector
What does the intake manifold carburetor pad look like? I think a 4 hole gasket is better in most cases.
When I use later carburetors on those intakes I'll also block the holes at the end of the "hot-slot". Then I use the OEM gasket and make a slightly thicker metal plate for them and slightly longer at the front. At that point you can use whatever you want on top of it, including that newer model carburetor with the "U" shaped channel in front of the primaries. If you don't pay close attention to things with those intake you can end up with a vacuum leak and may have trouble figuring out why the idle quality isn't that good and the engine just isn't running like it's supposed to......
