Quad carb setup information help

rod7515

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Tim, I have purchased them and I have them in my cabinet because as normal I decided to go a different route and I bought the quick change pods that allow me to change springs without taking the side vacuum assembly’s off the carbs. I’m attaching pics so you can see a better view of carb set up. I do have both carbs tied together with vacuum hose.
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rod7515

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Tim, I’m reading the holley instructions on their carb tuning. Here’s a line about the slot and idle adjustment……. "The Tslot should be exposed slightly as shown. Not having any showing will cause a stumble as you apply the gas from it going lean. Having too much exposed will feed enough fuel to the engine at idle, to make adjusting the idle air fuel screws not have any effect, making it idle too rich. It is best to set the Tslot so the opening that is exposed is as long as it is wide, square. After doing this, make your idle speed adjustment using the secondary idle adjustment screw.’

I’m not home until Sunday night late to look at my carbs and haven’t found a pic that shows a secondary idle speed adjustment. Do you know if all holleys would have that? Just trying to educate myself a little more on what I will be doing. I guess I will pull both carbs off to verify from the underside of t slots?
I’m sure this will end up a long process until done.lol
Rod
 

rod7515

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Quick update on car. I’ve got the new trans cable in and sitting on the rack it seems to be adjusted and ready to drive. Now we just need the rain to stop. Been 3 straight days of rain and at least one more to go. As soon as it’s dry I’m going to start my tuning. I’ve been looking forward to this part for a long time but life has always gotten in the way. This month I should have some time to play.
Rod
 

rod7515

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quick update, the weekend looks like great weather. I plan on getting some valuable information before I/we start the tuning. I will get some good vacuum numbers as I drive which should tell us where to start and what changes to plan on attacking first. Is there anything else I should record other then rpm’s when I have hesitations.
Thanks, Rod
 

rod7515

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So here are some numbers from today. Keep in mind that I am working with 2, holley 600 carbs that have 6.5 power valves and size 62 main jets. The distributor has been recurved to have 12-14* of advance and all in around 2800. Base is at 22* @ idle So I’m at 35-36* total.

The issue I’m dealing with is a slight stumble when normal driving. There is no issue when launching car from idle in gear. Very quick with no hesitation that I noticed.

So I warmed the car up really well. Took it for a 3 mile drive which has flat, uphill and downhill. Fairly steep at start. Here are the vacuum numbers I had.

MPH. RPM. VACUUM
0- in park. 1200. 11
0- in gear. 1000. 7.5
25 in town flat. 1800. 14
35 coast slight down. 1700. 16
40 flat light throttle. 2500. 14-16
45 flat light throttle. 2800. 17
45 uphill moderate. 3000. 12

using light throttle there is a tip in hesitation. It’s very bad when engine is not totally warmed up. I should clarify there are no chokes. Both carbs have had them milled off. So where do I start? I plan on changing the secondary springs to the mid pressure spring before doing anything else to eliminate the possibility they let the secondaries come in too soon. Right now they have the lightest spring possible. Where to if that doesn’t cure it?
look forward to your thoughts.
Thanks Rod
 

Rat Bastid

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So here are some numbers from today. Keep in mind that I am working with 2, holley 600 carbs that have 6.5 power valves and size 62 main jets. The distributor has been recurved to have 12-14* of advance and all in around 2800. Base is at 22* @ idle So I’m at 35-36* total.

The issue I’m dealing with is a slight stumble when normal driving. There is no issue when launching car from idle in gear. Very quick with no hesitation that I noticed.

So I warmed the car up really well. Took it for a 3 mile drive which has flat, uphill and downhill. Fairly steep at start. Here are the vacuum numbers I had.

MPH. RPM. VACUUM
0- in park. 1200. 11
0- in gear. 1000. 7.5
25 in town flat. 1800. 14
35 coast slight down. 1700. 16
40 flat light throttle. 2500. 14-16
45 flat light throttle. 2800. 17
45 uphill moderate. 3000. 12

using light throttle there is a tip in hesitation. It’s very bad when engine is not totally warmed up. I should clarify there are no chokes. Both carbs have had them milled off. So where do I start? I plan on changing the secondary springs to the mid pressure spring before doing anything else to eliminate the possibility they let the secondaries come in too soon. Right now they have the lightest spring possible. Where to if that doesn’t cure it?
look forward to your thoughts.
Thanks Rod

I doubt that is a secondary issue. You can make the IAB smaller to get it a bit richer on transition. You can also open the PV sooner with those vacuum numbers.
 

j par

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I would try a larger pump shot in one carburetor and see if any difference... Cheap and easy...
I kept/keep a note book and keep very detailed notes of everything I did/do ....
It took quite a few tune and test days to get my carbs for my combination to o be happy...
Your not likely to get a silver bullet idea here or anywhere on the internet but more likely some good things to try ..
 

rod7515

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So after doing some Holley reading tonight I’m going to change my PV from the 6.5 to a 5.5. This should allow a quicker fuel dump opening.
Now j par. When you say add a larger pump shot are you talking about a nozzle change. If so do you drill larger or buy new. If not how am I to increase that pump shot?
I also want to get some blank air bleeds. I couldn’t figure out which ones to buy because McMaster car has so many to choose from. I think I’ve been told I will need some 6-32, 8-32 and 10-32 brass set screws. Does anyone no what numbers I need so I can drill them by hand?

This is going to be a fun ride. I want the car to run great and get the best fuel economy possible for what it is.
Thanks for all the help
Rod
 

Bewy

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Nooo, going from a 6.6 to a 5.5 PV will be a slower transition. Vacuum has to drop further before the PV opens & starts supplying fuel.
 

j par

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So after doing some Holley reading tonight I’m going to change my PV from the 6.5 to a 5.5. This should allow a quicker fuel dump opening.
Now j par. When you say add a larger pump shot are you talking about a nozzle change. If so do you drill larger or buy new. If not how am I to increase that pump shot?
I also want to get some blank air bleeds. I couldn’t figure out which ones to buy because McMaster car has so many to choose from. I think I’ve been told I will need some 6-32, 8-32 and 10-32 brass set screws. Does anyone no what numbers I need so I can drill them by hand?

This is going to be a fun ride. I want the car to run great and get the best fuel economy possible for what it is.
Thanks for all the help
Rod
If you put @ before someone's handle they get a notification...
Yes you can buy bigger nozzles... Myself I'd try just doing it in one carburetor and see what happens... Again my carbs are not set up exactly the same... Mine are set up for street performance not wide open drag racing... Also I have different carbs that have Holley, Edelbrock, and stand alone part's... But in the end they're vessels to mix air and fuel in the perfect mixture at the perfect time or as close as you can get....
 

rod7515

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Bewy, I went back and reread the article from holley and I think I had it backwards. Am I right in going to a 7.5 or 8.5 to open the valve earlier.
Also I ordered some blank Air bleeds in 3 sizes. 6/32, 8/32 and 10/32. I got drills add taps to change and add them. I will do the power valve first.
Let me know if I’m on the right track.
Thanks Rod
 

Rat Bastid

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Bewy, I went back and reread the article from holley and I think I had it backwards. Am I right in going to a 7.5 or 8.5 to open the valve earlier.
Also I ordered some blank Air bleeds in 3 sizes. 6/32, 8/32 and 10/32. I got drills add taps to change and add them. I will do the power valve first.
Let me know if I’m on the right track.
Thanks Rod

Yes, the higher the number the sooner it opens. If you want to change how much fuel is added when it opens that’s controlled by the two holes behind the power valve. If they are not already threaded, they need to be. 8-32 is the size I use. Once you get your primary main jetting correct for CRUISE, you leave those alone.

If you need to add or subtract fuel (on the primary side) you do that with the power valve channel restricters.

Once you get a handle on the power valve, how it actually works and how to use it you’ll be able to out tune all your buddies.
 

rod7515

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Thanks Rat, you know I’ve leaned very hard on you for advice getting to this point. I don’t see that changing going forward. Lol. I will make the PV change and check to see if the metering blocks are tapped or not. I’m guessing I should pin the current passages so I know the starting point size that I will drill the 8/32 plug to. A question would be how far do I drill down into the current passage. The bleeds I bought from McMaster Carr are 1/8’ long for 6 & 8/32 and 3/16 for the 10/32. I’m away this weekend so it won’t be until next week before I do the change. Thanks for everyone’s suggestions and help.
Rod
 
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