I need tuning help. I have a modded 302, with a 600 cfm holley 4160,and just wanted to know what size anyone would suggest, or just what sizes other people were using. Any help would be appreciated!

 

If its running too rich, take the jets down one or two notches at a time. You just have to see what it likes.

When it gets too lean it will surge and maybe pop a little in the carb.

 

I would start around #65 jets, but every engine is different and will need fine tuning. Like Superdave said, change them in 2 size increments. Say go from 65 to 67 or whatever. This is what Holley suggest.
Jimmy

 

Is 600 cfm possibly too big? I have done head work, intake, cam etc. It doesnt seem like 600 would be overkill, could someone confirm or tell me different?

 

302ci X 5500rpm= 1661000 / 3456 = 480 cfm.
@5500rpm you can use about 480cfm @ 85% volumetric efficiency. A 600 is fine because it it vacuum secondary and will only open if the engine needs it.
By the way, the 87-93 5.0EFI engines used about a 600cfm EFI set up. 60mm throttlebody.
Jimmy

 

I seem to be running rich, could tuning the accelerator pump circuitry help?

 

Have you checked the engine idle vacuum to see what it is? You may have a blown or wrong sized power valve. It should be nubered around 1/2 of what the engine vacuum is. If it is an automatic, check it in gear with your foot on the brake.
Jimmy

 

mustangman66cpe

Running rich at idle, smells real gassy? I'd look at the jets. Could be other issues. But I would check there size and jet down a little to see if it helps.

 

well, i have been doing the exact same thing with my 65 stang with 302.
when i bought it , it had a 750 holley 4160 on it.....ran great but i suspected it of being to rich ( 72 jets ), anyway that holley mysteriously started idling weird......so one day im gonna take it apart.again to see what i missed. then i had a 750 edel on it.wanted that carb for my f-100....so im playing with a holley 600 now. it had 41 jets, way to lean and it ran badly..so tonite i went and got some # 69 jets, and maybe in a week or so ill see how it runs...........
about the rich running of yours.......another thing thats a must on holleys is the right number power valve......most holley power valves that come in the carbs open at between 7 and 9 i believe........if you have a lopey cam and low manifold vacuum at idle, the power valve will open causing a rich condition so check that as well.........put a vacuum guage to a manifold vacuum source and see what it reads.....then buy a power valve that opens a point or two below that ( if you had 8 inches of vacuum you want a 6.5 or 7 power valve) . if you pull more than 10 inches or so of vacuum it shouldnt be a problem.......but check it while you have it apart..........
a 600 cfm should be fine.........even a 750 would work if you tuned it right.so you should be ok......the above formula that was stated above is a good guide, although for some reason it always seems a little small of a number when i use it but i think this is due to the fact that it doesnt take into account thats if the carburator is 100 percent efficient.and id immagine there's enough variables to justify larger carbs than the formula suggests........but it is a good guide and 600's will work on about anything. especially small blocks.

 

Most stock power valves open at 6.5 inches of vacuum IE 65 part number. Check the vacuum idling in gear if it is an automatic. You want the powervalve to be about 1/2 of idle vacuum. If you have 10" of vac, then you would want a #55 power valve etc.
If you can turn the mixture screws all of the way in and the engine keeps running, then the power valve is either wrong or blown.
The jets can effect idle to a certain degree, but it will still die with the screws all of the way in reguardless of jet size. The powervalve bypasses the metered circuit thus is un effected by the mixture screws.
Also, with it idling, look down the carb and make sure that there is no fuel dripping out of the venturi's, this would indicate that a float is too high of something is in a needle and seat if there is fuel present.
Jimmy

 

perhaps my power valve suggestion was wrong..........i know i read sevral places that the number need only be one or two numbers below vacuum............perhaps this is for more strip than street???
also, there's the high flow power valves i see now, are those any better or over kill???
i put 69 jets in my 600, and a 5.5 power valve in ( it pulls 7.5 ) and it does die when the mixture screws are closed off, so i think its ok but i am having some idle irregularities..........has a bit of a stumble off idle which may be the accelerator but that doesnt explain why its less stable at idle than it was with a 750 on it.......any suggestions on what to look for???? these things are simple but man, some times....................lol...

 

I would try a 35 powervalve. Yours is opening as soon as you give it gas. It may be the cause of your stumble by over richening the A/F ratio. You can also adjust the spring a bit on the accelerator pump linkage. But only if no fuel squirts out of the nozzles when you first open the throttle.
Jimmy

 

i'll give it a try, i think my next investment will be re-usable float bowl and metering block gaskets....lol..........go figure...........

 

You can also spray them with silicon spray. This will help them from sticking as well.
Jimmy