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What's the history on the carb.....when was it rebuilt last. If you don't know or are going to guess, I'd suggest spending the $25 bucks on a book on how to rebuild them, and also watch a few youtube vids to learn about them. They are not hard to rebuild or adjust, you just need to understand how they work and where the separate circuits are in the carb.
It could be as simple as an idle or fast idle adjustment or possibly the thing is all gummed up and needs some love.
What's the history on the carb.....when was it rebuilt last. If you don't know or are going to guess, I'd suggest spending the $25 bucks on a book on how to rebuild them, and also watch a few youtube vids to learn about them. They are not hard to rebuild or adjust, you just need to understand how they work and where the separate circuits are in the carb.
It could be as simple as an idle or fast idle adjustment or possibly the thing is all gummed up and needs some love.
brand spanking new. as i said i played with fast idle etc. putting it in drive drops me down to abou 500-550 rpm's rough idle. suggestions point to a vac leak which may explain low vac and/or jumping needle. will spray carb cleaner around areas where there me leaks perhaps that may be it. remember I replaced the intake manifold very possible there's a leak where I should have put more silicone, etc. let's see tomorrow. it's pouring.
I think you are on the correct path, and you likely have a vacuum leak to address. The leak could even be at your transmission, the oft-removed intake, the carb base, or even your brake booster. So if the spray-down trick doesn't work, try plugging some vacuum lines to isolate the leak. You can get a set of assorted plugs at a car parts store, or from Amazon, if you don't have them already.
You'll need to use the gauge on your Mity-Vac when you do the idle mixture adjustment (follow Holley's instructions), and not just turn screws to see what works. I use a Lisle 20300, which is a bit less cumbersome.
Pull all the vacuum lines that are attached to the carb ( except the vacuum advance) and then plug the ports on the carb and intake manifold where you removed the lines from. This should isolate any leaks you have downstream of the carb, so now you can adjust the carb and get it right. Going around the carb base with an unlit but flowing propane torch, or some carb cleaner is a good way of finding a vacuum leak.
If it's brand new it should be reasonably close. An inexpensive wideband AFR gauge makes tuning a breeze....something like this https://www.summitracing.com/parts/avm-30-4110ns
So check it out. I did the carb cleaner spray trick before so I did it this time. No advance anywhere around the intake manifold, etc. I removed the 3 way manifold connection by the carb and plugged it with a metal plug designed to fit there (I have a bag of them different sizes) to see anything changes. No leaks that I can find. None by carb, brake booster, manifold, etc.
I used my mighty vac again on the 3 way manifold connection with a/t trans line off and headlights off. capped. same pressure about 15 hg (when I squeeze the line shut it stops jumping around and stays at what pressure it was at. 15 every time.
NOW CHECK THIS OUT.
Took the 2 idle mixture screws on both sides of carb that NEED TO BE ADJUSTED AT THE SAME TIME, does nothing for you UNLESS YOU CAN SEE HOW THE VAC INCREASES. so, I turn the screws completely clockwise to close them, then counter 1 full turn. start the car up with my vac connected. shows 15hg. SHUT OFF THE CAR (this is important for accuracy) and turned the 2 screws counter once again a full turn. started the car and my vac showed a change to 19hg. Did it again and saw no significant change at all. I'm sure now I have to combine this with other changes but I STOPPED at this point.
What changes did I see? Car is NOT shaking horribly when placed in gear. why? because my rpm's are up around 625. I can keep fiddling it to get it a bit more stable but for now it's really good.
What happened to my timing you ask? lol. It's the same. JUST in case I rechecked it and it's where it has been for mechanical (36x300). The vac advance connected changed? Went from 20 to 22.
The light gun is just there for rpm readings. Notes between pics.
turn them at the same time WITH CAR OFF EVERY TURN. notice mighty vac and rpm's. wants to shut off and pressure was low. now notice mighty vac. I brought my rpm's down from 800 to 750 to 700 ish area. feels good.
Last edited by michael lamoglia; May 19, 2021 at 07:40 PM.
yes brother! thanks. I want the car while in gear a bit smoother so I will fiddle JUST A BIT with idle mixture. Headed to the vette meet tonight and will have a rack of ribs for all of us!
I agree with Bikespace, you pretty much have it right with 19" of vacuum. Taking it for a run will clean up the plugs and give you an idea of where it's at.
I agree with Bikespace, you pretty much have it right with 19" of vacuum. Taking it for a run will clean up the plugs and give you an idea of where it's at.
feels good. Needs a bit more tweak. Wants to big down in that 1 second between stop and giving it gas. Then it’s fine. Too rich? Also made it to the meet!
