carb jettin

[Ron816]

have a newly rebuilt 440, basic 30 over 11:1 stock cam rockers etc, have a holley 850 which has 80 primary jets, definitely running rich, question is what jet size would I be looking at for both primary and secondaries?

 

[silversedan]

i'd try 76 square, if running power valves, also make sure the power valves are good.

 

[TetanusShot]

What silversedan said, I was going to suggest 74 primaries 76 secondaries.

 

[coloradodave]

Ron816, we really need more information. Have you pulled the plugs and checked the coloring, as too lean at idle and low speed can also make your eyes tear-up? I would recommend first getting a handle on where your initial timing is set and how much total timing you have and at what rpm. Then, using a vacuum gauge, set your idle mixture screws to the best 'lean' idle setting. After that, make a full throttle run (as long as there isn't any pinging) and chop the throttle clean, coasting to a stop. Pull as many plugs as you can without burning yourself and check the coloring. Recommendations can be made if you post pictures of the plug insulators (business end). If the power valves are leaking, you won't be able to get any adjustability on your idle mixture screws.
Good luck...

 

[Ron816]

Set off idle with vacuum can smell fuel eyes burning checked plugs black and sooty
Kicking off idle bad popping thru carb it's a new Holley 850 just think too much carb

- - - Updated - - -

Also seems sluggish

 

[HEMI-ITIS]

What vacume does it pull at idle? What size power valve? That could be the issue,but as said also check the timing and timing curve.

 

[coloradodave]

Ron816; Carburetors don't work like that. If everything is right with that carburetor it will idle and drive fine. Black, sooty plugs are a good indication that either the power valves' closed value is above what your available vacuum is, the float settings are too high, the fuel pressure is pushing the needles off the seats or your ignition system has a problem. Bad popping through the carburetor is not normally a carburetor problem, but a timing or valve setting problem. I wouldn't be so quick to dump the 850 as I feel that your problem may not end with a new carburetor. Diagnostics before throwing parts at a problem. Words to live by...

 

[Garys1969RR]

I am running an 850 double pumper Holley on my 451, and it works great. I had to jet it up to 86 all around as it was too lean at first. But I also run a mix of 2 gallons of E 85 with 6 gallons of race gas to raise the octane. This requires a larger jet.

- - - Updated - - -

I think something else is wrong with your motor. Please give some specs on your build. What is the deck to piston top clearance ? Should be around .040" What heads, cam specs, intake, are you using headers? Try putting a plug in the primary power valve, just to see if that helps, your cam may not be drawing enough vacumn to close it. Check cam timing. I have seen builders install it on the wrong mark, or a link off.

 

[Ron816]

I rebuilt motor nothing fancy stock heads, stock intake, stock cam, I took advice changed primary to 74 secondaries to 76 with 31 spray nozzle, advanced timing a couple degrees definitely an improvement haven't had a chance to test ride will let you know what I come up with,

- - - Updated - - -

pulling 40lbs vacuum, believe power valve is 6.5

 

[coloradodave]

Ron, you might try another vacuum gauge. 40" is highly unlikely...

 

[Ron816]

Sorry was writing while driving 4"

 

[coloradodave]

Really? Either you have a really, really, nasty race cam in that motor or something is way off in your timing (ignition / cam) and thus is a very likely reason that you're running rich. If the Holley has 6.5" power valves (likely unless someone changed them) that means it takes at least 6.5" of vacuum to hold them closed. Less than that will let raw fuel dump, which, at lower rpms, will cause the motor to run very rich. Find the source of low vacuum and you'll solve your problem.

 

[Ron816]

I'll re-check vacuum

 

[HEMI-ITIS]

What vacume does it pull at idle? What size power valve? That could be the issue,but as said also check the timing and timing curve.

Like said before,verify vacume and power valve size:blob1:

 

[Ron816]

Changed jets 74 prime 76 second no more popping just a little stumble on initial Accelleration vacuum 12 power valve 6.5 should I drop down in valve size?

 

[HEMI-ITIS]

Now we are getting some where.If you have a solid 12 inches of vac,I would go 9.5 or 10 on the PV and that would take care of that lean stumble.

 

[Ron816]

You would go that large I thought the formula was roughly half of what vacuum was for power valve size

 

[HEMI-ITIS]

About 2 on a modified deal.

I don't use power valves

 

[Canyon707]

I have no power valves and run 90 jets 4x it runs a tad rich but, very close. When I got this car it had 96 and 95 jets and both power valves. All this made a big change. Made and 11 second car into 10.8 10.7 consistently.

 

[coloradodave]

Race cars verses street cars: Different animals and WAY different tune-ups.