Holley carb jetting 101

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Thrasher

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Took my freshly rebuilt 360 down the road today for the first time... runs well, but it smokes more than it should and it idles rather rough (even rougher when I put it into drive/reverse) My first guess is that I need smaller jets for the carb. The setup:

360 block
1971 J-heads from a 340
Edelbrock air gap intake
Dual exhaust all the way through with stock 318 manifolds
Cam - Duration 262/272, Lift .420/.442 (similar to stock 340? My father bought it a few years ago and never used it...)

Carburetor is a Holley street avenger 670.

In the manual the specs say:

Primary metering jet - 65
Secondary metering jet - 68
Pump discharge nozzle - 0.031
Primary power valve - 65


Any recommendations? :dontknow:
 
There was a post on here awhile back about the street avenger carbs losing their plating inside the fuel bowls, just a thought, something to check.
 
Thrasher said:
Took my freshly rebuilt 360 down the road today for the first time... runs well, but it smokes more than it should and it idles rather rough (even rougher when I put it into drive/reverse) My first guess is that I need smaller jets for the carb. The setup:

360 block
1971 J-heads from a 340
Edelbrock air gap intake
Dual exhaust all the way through with stock 318 manifolds
Cam - Duration 262/272, Lift .420/.442 (similar to stock 340? My father bought it a few years ago and never used it...)

Carburetor is a Holley street avenger 670.

In the manual the specs say:

Primary metering jet - 65
Secondary metering jet - 68
Pump discharge nozzle - 0.031
Primary power valve - 65


Any recommendations? :dontknow:
Click to expand...

Is it rich just at idle and or on the road?

For on the road, your specs look OK. You wouldn't want bigger jets if it's already rich on the road.

At idle, your mixture screws should both be out about 1 1/8 to 1 1/4 turns, then increase the idle speed until it smoothens out. (For auto and manual brakes around 825 to 850 rpm for your combo.)

Holleys are wet flow tested before they are boxed. The jets are last thing I would change.

Maybe a vacuum leak??? thereby adding more fuel to compensate for rough idle?
 
NiceFishEh said:
Is it rich just at idle and or on the road?

For on the road, your specs look OK. You wouldn't want bigger jets if it's already rich on the road.

At idle, your mixture screws should both be out about 1 1/8 to 1 1/4 turns, then increase the idle speed until it smoothens out. (For auto and manual brakes around 825 to 850 rpm for your combo.)

Holleys are wet flow tested before they are boxed. The jets are last thing I would change.

Maybe a vacuum leak??? thereby adding more fuel to compensate for rough idle?
Click to expand...
Actually I misspoke, the idle in park is not bad (I adjusted both idle mixture screws 3/4 turn leaner than it came out of the box) It idles ok... just not as smooth as I would expect with that mild of a cam. When I punch the gas in park it does hesitate just a little bit.

I was actually thinking that the jets I have now are too large. Before I go changing jets I will check the vacuum pressure first 8)
 
Thrasher said:
Actually I misspoke, the idle in park is not bad (I adjusted both idle mixture screws 3/4 turn leaner than it came out of the box) It idles ok... just not as smooth as I would expect with that mild of a cam. When I punch the gas in park it does hesitate just a little bit.

I was actually thinking that the jets I have now are too large. Before I go changing jets I will check the vacuum pressure first 8)
Click to expand...

Out of the box is colse to where it should be for that carb, and probably a little lean to begin with. 3/4 turn in is a lot. Let your vacuum guage be your guide.

Is your electrical in good shape? Is it getting 12v before the resistor and 8v after?

You could up the squiter to 35. I found it to be to much for my 650. Went back to the 28.

Jim

DSCN1219.jpg
 
The 670 should feel right at home on that setup. I'm running the same carb and it was great right ootb. The only problem I had was just like you I turned the mixture too low causing a lean condition that made it surge and hiccup when driving. As far as the plating falling off, I think that is just on the older models and Holley replaced one members carb no questions asked once he contacted them.
 
Thanks for everyone's helpful suggestions! I'm actually waiting on a worm gear bearing for a steering box, and after it comes the screwdrivers will be flying! :read2:
 
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