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600 cfm holly on a 305

T

tellboy

Not-quite-so-new-guy
Jun 2, 2018
21
17
3
70
newzealand
Greetings folks, happy new year 25
havent touched the elky for a year - life just got in the way. now i just need to get it running smoothly.
The engine is a 305 fitted with headers, HEI distributer, and Holly 600
the carb came new with #66 main jets which i dropped down to #64 and it runs, but very rich, to the extent that sometimes fowls the plugs with over supply of fuel.
Has someone else done this combo and what jetting did you end up using, i know its trial and error but a bit of advance knowledge is helpful. cheers Terry
 
Its not the Jet size doing it. Is the carb new, or are you saying that is what it came from the factory with? I have run 305's with both 600 and 750 vac secondary holley's and never touched the jetting.
 
Hello, the carb is a brand new 4 barrel holly and came with #66 jetting. i set it up as per the manual, float levels, fuel pressure etc but its definitely over fueled
 
Choke operating properly? What happens if you tie the choke wide open?
 
I've read stories about even brand new carburetors having junk floating around inside them from holley and other manufactures after being built.

This may sound like a chore, but i would suggest taking it completely apart, use carburetor spray through ALL the passages and then use compressed air to clear all the passage ways in the main body, base plate, metering block, fuel bowls, etc.

If you decided to skip the deep cleaning part, with the engine off, make sure your idle mixture screws are 1 1/2 turns out, turn inward gently till both are fully seated, then turn outwards. After the engine is started and fully warmed up, turn the idle mixture screws inward to get the highest vacuum reading, you need a vacuum guage for that part, you will definately hear the engine idle change, both idle mixture screws must be equal in number of turns.

What idle rpm and initial timing are you running, is the 305 completely stock?

 
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At idle look down secondaries. If dripping fuel, replace o-rings on transfer tube.

Pull front (primary) plate. Check power valve. Could be bad or wrong size/setting.

Idle too rich is controlled by idle mixture screws. Screw them all the way in and then back each one out to 2 turns, see if that improves.

Check out some David Vizard and Thunderhead 289

Also just follow the vid shown above.
 
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first check the float levels front and back if you take that plug out when running and fuel pours out its overflowing you will need to adjust the float there are plenty of web sites showing how to adjust them
 
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Another tidbit.... if you have a way to check your mechanical fuel pump pressure while idleing, do it.

The off the shelf units from auto parts stores typically pump out way too much even though the manufacture says 5psi, they will vary, i've had 10+psi before, and eventually it killed my MrGasket 15psi pressure guage i was using.

I myself had to correct that excessive fuel pressure problem by going with an aftermarket unit thats preset internally to 6psi, i highly suggest you do the same, theres one by "blueprint" engines company that offer a 6psi unit thats reasonably priced.

https://blueprintengines.com/produc...nt=sag_organic&utm_campaign=sag_organic&gQT=1
 
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Or you could add a fuel pressure regulator
 
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