Holley Carb ?

[Wayne P.]

I have a Holley double pumper 650 on my 327. Seems to be too much carb with primary jets at .66 . The plugs were fouling up after awhile. I changed from a/c 43 to a/c 45 . Problem went away for awhile then starting again. Makes car bog under load 2nd gear .
I was thinking of putting .64 main jets in .
Any thoughts. Thanks

[Harry S.]

Re: Holley Carb ?

Wayne, a 327 what?, what hp?, cam? etc.

[Ken A.]

Re: Holley Carb ?

GM recommends #77 jets at all 4 corners. Sounds like a blown power valve. Use 45's or 46's for the street.

[Clem Z.]

Re: Holley Carb ?

I have a Holley double pumper 650 on my 327. Seems to be too much carb with primary jets at .66 . The plugs were fouling up after awhile. I changed from a/c 43 to a/c 45 . Problem went away for awhile then starting again. Makes car bog under load 2nd gear .
I was thinking of putting .64 main jets in .
Any thoughts. Thanks

DP holleys are jetted rich on the jets and leaner on the power valve restriction for racing. you need to increase the PVR area and decrease the jets to the same as a 650 vacuum secondary carb. also reducing the idle fuel restriction by inserting a piece of .015 wire into the restriction will lean out the idle

[Wayne P.]

Re: Holley Carb ?

Thanks for the info. running comp cam 365 327 300hp
Like I mentioned runs great when you replace plugs then starts to foul up plugs around the 75 mile mark.It is a new carb and power valve is 4.5 AED 650 carb. I believe total vac is 13 Tempermental , replaced main jets with 63 not much difference. I will bolt back on by edelbrock 650. It ran fine.

[John H.]

Re: Holley Carb ?

Thanks for the info. running comp cam 365 327 300hp
Like I mentioned runs great when you replace plugs then starts to foul up plugs around the 75 mile mark.It is a new carb and power valve is 4.5 AED 650 carb.
I believe total vac is 10

Wayne -

Double-pumper Holleys aren't a great choice for a normal street-driven combination; they're difficult to tune for balanced operation, and need the kind of modifications Clem noted to get them to run right in other than "race" mode.

A 600 or 650 with vacuum secondaries is a FAR better choice for the street, as the '64-'67 SHP 327's were originally equipped (they had 585's).

[Jim T.]

Re: Holley Carb ?

I have a Holley double pumper 650 on my 327. Seems to be too much carb with primary jets at .66 . The plugs were fouling up after awhile. I changed from a/c 43 to a/c 45 . Problem went away for awhile then starting again. Makes car bog under load 2nd gear .
I was thinking of putting .64 main jets in .
Any thoughts. Thanks

Wayne I have been using a Holley650 #6210 double pumper on my 68 Corvette 327/350 since 1974. Have not experienced the problems you have. Still using the original jetting that came in this Holley. I don't use AC plugs. Have always used Champion J12 sparkplugs. Champion plug tips extend more from the base of the plug than the AC plugs. Car runs/performs great. I like the absolute control of the secondaries with the Holley double pumper, this ole car still moves pretty good when the secondaries are activated.

[Dick W.]

Re: Holley Carb ?

I have found that vacuum operated secondaries work the best on the street. You can tweak them, 50cc pump if you need it, different spring in the secondary diaphragm, etc.

[Clem Z.]

Re: Holley Carb ?

holley says only use DP on the street if you are running deep rear gears like 4:11

[Timothy B.]

Re: Holley Carb ?

Wayne,

I agree that a 600 Holley vacuum secondary carburetor should be fine for your 327 engine regardless of the camshaft.

It's my understanding the double pumper carburetors have a rich idle circuit so just changing the main jet will not lean the carburetor because most street driving employs the idle circuit as well as the main circuit. The transfer slot is probably contributing more fuel than the main circuit cruising around on the street.

Many times people feel the bog when mechanical secondarys open and think the car is faster than when they can't feel the secondary open. It's the opposite, the vacuum operated is better suited for a street driven car and the engine runs faster. As long as the motor runs to 5500-6000rpm there is nothing wrong with the vacuum secondary operation.

All this does not mean you can't tune the carburetor to work but it requires reducing idle feed restriction to start then maybe air bleeds and on and on so it's better to start with a properly matched carburetor for street driving.