i put the following motor in my 32 ford highboy; 350 chevy 30 over with comp cams hydraulic roller #08-432-8 and 1.6 roller rockers. The compression ratio is 10.3:1 It has Edelbrock performer aluminum heads and an Edelbrock performer RPM air gap intake. The carburator is a holly double pumper 750? with ; Primary jets 68 shooter 40 secondary jets 68 shooter 35 power valve 6.5 The plugs are Autolite 3924 and it runs rich I'm at 4000 feet above sea level. where should I go from here ? lower jet size ? by how much? better choice of spark plug?
What's your timing set at? You should be able to run 20* initial, 12* mechanical and 10* vacuum advance with that set up and elevation. Hook your vacuum advance to manifold vacuum then turn down your idle. If it's still running rich go down to a 4.5 power valve. I ran a similiar combo at the same elevation. You need lots of initial timing due to low air density.
It seems to me that a 750 double pumper is too much carb for your build and 4000' elevation. What trans are you running and what rear axle ratio? May be the wrong cam profile for an automatic.
Thanks for the suggestions. The car has a richmond 4 speed and 4:11 rear. The distributor is MSD with no vacuum advance, timing 16 initial 36 full advance
I'm sure you know but just in case, the amount of manifold vacuum available is where you select which power valve to run. Most Holley books have a chart that help you select the correct valve.
Is it running rich just at idle or is it rich throughout all ranges of operation? The power valve is probably going to need to be changed for a 2.5 or 3.5, the floats need to be correct also. The pump shooter in the front might be a little big, but if it has no hesitation or stumble it's probably okay.
750 is perfect for that setup. You can get a block with externally adjusted jets from Percy's. I am currently running one. Be sure to use the gaskets that come with the kit. The distance between the bowls will increase, if that is a concern. I just made my hose a bit longer...
Run your idle screws in to stop, back them out 3/4ish turn and might have to back them out another 1/4 or so. Power valve should be about a 4.5 The jetting seems odd, the secondaries should be about an 80 without the powervalve, primary about a 70. Change the squirts to 28 primary, 31 secondary.
A couple of things jump out at me on your setup. Number 1, the square jetting on the primary/secondary. I think stock jetting for a 4779 doublepumper is something like 70 for the primary and 80 for the secondary. The 68s should be close to right for your alt. You might go down to a 66/67, but I think that's about all I'd drop it. I'd kick the secondaries up to around 78s. The other thing is the front squirter (40) is WAY fat, I'd try a 25/28 or so in it. Other than that make sure your choke is opening, the power valve isn't ruptured and that the floats are set right. Then I might start looking at timing. OJ, looks like you posted while I was typing. The fact that our answers are real similar should scare you---------a LOT!
Yep! I got a "-2" newer version of that carb... Should go with a 28-32 shooter on the front and back... Unless your running a 50cc "Reo" acc. pump..
thanks for the suggestions, I always find the hardest part of an engine build is getting the carb set up right.
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