Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

opinion on primary rod / jet change

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77cruiser:
How much compression do you have? I run mine with Profiler heads @ 38 deg. 9.8-1 CR.

kilowattkid:
10.5

kilowattkid:

--- Quote from: 77cruiser on November 27, 2024, 11:26:37 AM ---How much compression do you have? I run mine with Profiler heads @ 38 deg. 9.8-1 CR.

--- End quote ---

Do you run yours locked out at 38 degrees? Are you running a MSD box. This video shows a guy testing a locked out distributor with a CDI and shows a loss of like 10 degrees of timing at 5000 rpm.

https://www.youtube.com/watch?v=XN8NBCeKTFs

77cruiser:
No 18 initial & 20 mech. in around 2500, HEI.

kilowattkid:
Still trying to wrap my head around this before I go tearing into it, which is probably going to be after Christmas.

I get that a regular inlet seat could cause low flow issues and if that was the case I'd think that going from 75 jets to 77's would make the problem worse. It actually improved with going to 77's and the lean pop was lessened.

Digging deeper, this carb was for a 1974 SBC truck rated at 185HP and came factory with 75 jets and 43 rods. My 385 SBC I'd certainly think that it is at least double that and should be tickling the 400HP range.

From the paperwork provided they stated a high flow inlet seat and also a different primary power spring to match my cam. I can only assume that is correct. I just can't wrap my head around a 1974 stock rod / jet combo will work with a more performance oriented engine. Adding to my confusion is that my other carb I was running had 71 jets and 36b rods which is less area for fuel to get through.

BTW, this is the chart I was using looking at jet / rod combos - http://www.corvettefaq.com/c3/QJetTuningPaper.doc

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