4150 holley 650 jet size?

FULL-THROTTLE

New Member
Mar 9, 2015
5
ma
Anyone running a Holley 4 barrel 4150 carb on a Sbc? I have a 70 z28 010 4 bolt main and original 041 heads, the block was bored .030 over and the heads completely rebuilt with heavy duty springs, the cam is just a bit over stock and i have 9.75:1 compression ratio, I have main jets of 68 and secondaries of 74 and the plugs are wettttt and black of carbon. Is there any chance this carb was not built for this kind of build? A professional shop did the motor for me. The motor wont idle under 1600 and as the rpm’s increase the better it sounds. Timing is 8 btdc and the distributor is a brand new Mallory hei. Any help is appreciated. I am ordering a jet kit in a few minutes.

Fran
 

muscl car

Veteran Member
Lifetime Gold Member
Jul 8, 2001
23,961
Gallatin Tennessee
Your jetting is very close to what comes in the carburetor from Holley .....

Primary #67 secondary #73

Your timing seems retarded I would go with 10*

Have you checked float level and A/F settings ???

Do you notice fuel vapor in either primary or secondary side , could be an indication of a stuck needle / seat or possibly a blown power valve could be your issue
 

muscl car

Veteran Member
Lifetime Gold Member
Jul 8, 2001
23,961
Gallatin Tennessee
Floats are set just below sight window when i remove brass plug, both power valves are brand new. ?????


As I mentioned previously do you notice any fuel vapor coming from the venturi's after the engine is shut off . Also notice any fuel dripping from the venturi's at idle . That would be from trash / debris on the needle / seat . This would definitely cause driveability issues
 

73 Z

Veteran Member
Jun 9, 2007
1,263
Los Angeles, Ca
Anyone running a Holley 4 barrel 4150 carb on a Sbc? I have a 70 z28 010 4 bolt main and original 041 heads, the block was bored .030 over and the heads completely rebuilt with heavy duty springs, the cam is just a bit over stock and i have 9.75:1 compression ratio, I have main jets of 68 and secondaries of 74 and the plugs are wettttt and black of carbon. Is there any chance this carb was not built for this kind of build? A professional shop did the motor for me. The motor wont idle under 1600 and as the rpm’s increase the better it sounds. Timing is 8 btdc and the distributor is a brand new Mallory hei. Any help is appreciated. I am ordering a jet kit in a few minutes.

Fran
If it won't idle under 1600rpm @ 8 btdc there must be a vacuum leak, or the carb transfer slots are exposed to much and the idle is set high to compensate. Is this an auto or manual
 

G72Zed

Veteran Member
Sep 8, 2015
4,220
Canada
All add to the already great responses from the members here.

1- I have seen "New" power valves that leaked.
2- ""cam is a bit over stock" if this is meaning a little more aggressive, as in dur. @ .050 and intake closing, AND you have lowered the SCR to 9.75:1, that has "need more initial timing" all over it.
3- These engines came with the Holley 780 for a reason, why was a 650 used, unless changed to open plenum
4- If the engine is struggling in the idle/transition and low rpm cruise dept., the issue is not the main jet, but in the idle/transition circuit for the most part .

What is the actual part number/style of 650 Holley you are using.
 

STUCKINCALI

Member
Apr 18, 2020
38
Ca
the distributor is a brand new Mallory hei.
Have you verified you have a full 12VDC at the positive lead to the HEI coil? 1970 lead would be a resistor wire for points and the distributor would not achieve optimal spark (if at all) with the resistor wire in place. Just another thought...
 

MadMatt

Member
Sep 14, 2007
93
Montclair, VA
Timing, 100%. Start with 18deg adv. and of course check for vacuum leaks but that should lean you out so I doubt that.

It should also be about 36-38deg total, with mech/vac at roughly 3k-3.5k with what you have said about that build.

Try that first and let us know.
 




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