Holley 390 CFM Accelerator Pump

5851 and 37: The distributor I am using is a Mallory dual point distributor with mechanical advance that I converted to electronic with a Pertronix kit. It ran fine with dual points but, I decided to try an electronic unit 5 years ago when installed an electronic Mallory Unilite kit. The Unilite modules kept burning out so I finally installed the Pertronix kit which is what I have now.
You can see the part number info. in the photos.

Pertronix does make a kit for the stock 239 Load-o-Matic distributor.

I realize this won't help as your using a SBC distributor.
 

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Last edited:
tUNE WITH VACUUM GAUGE INSTALLED ..

crankster said
It's important to realize that engine vacuum is the only thing holding the power valve closed. The power valve should remain closed at all times other than demand for power, acceleration, under load etc. If the wrong value is selected, or it is defective, it will constantly dribble fuel.

A 6.5 power valve would remain closed as long as vac is above 6.5 , then as throttle is opened and vac goes below the 6.5 setting the power valve would open adding enrichment ........check with vac gauge , pretty easy to get the perfect setting allowing engine to run really well........
 
Mr. Linder, Thank you for that very clear explanation.

QUESTION:

I have read that the power valve should be selected based on the vacuum at idle. Is that true?

If that's true would using a #9 or 10 power valve be correct if the vacuum reading at idle is 19 in?

Thank you.
 
The problem is carburetor instructions are a little bit vague or don't fully explain what is going on with a power valve. A mechanic's vacuum gauge plumbed into the cabin is really useful to get a handle on how the engine handles different load and power settings and terrain. A 6.5" power valve is a good safe choice for many engines, but a performance engine with a lumpy camshaft, especially at any sort of altitude, would quickly run into problems. If you know what vacuum your engine pulls when cruising along on flat highway, that is really useful for selecting a close cut power valve #.

A defective power valve, or a # mismatched to that particular engine configuration can really skew things, eapecially reading plugs. Trying to select proper jetting for example. It's also possible to get defective power valves right out of the box. Testing with a Mityvac before installation is a good plan, to weed out duds. Like many other reproduction auto parts the quality isn't always there compared with brand name or NOS. I haven't much luck with the ersatz no-name power valves holding up to today's crap gas either. A year if lucky.
 
I have a Vacuum gauge mounted under my dash. I get a pretty consistent 17-19 in. at idle. I dont think the power value is my problem but i will replace it when i do the rebuild. Still waiting on the kit.

19Fordy.... any particular reason you use the plugs you do?
 
you only have a 390 not a 600 i would definatly steer clear of a 50cc pump that a lot of fuel in a short time you may need to change the cam and/or adjustment if its stumbling but i dout you would ever need 50cc on that carb
 
37: I use the NGK GR4-2635 because they were the ones recommended
by Mark Kirby (Motor City Flathead) in 1999 when I bought the heads from him.
 
Thank you, Everyone for your help.

I finally got to rebuilding the carb. The Accelerator Pump diaphram was leaking and the small orange rubber check valve was in pieces. Probably from our modern ethanol gas.

It's back together and fired right up.

Thanks Again All.
 
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