Holley carb help...

[69GMC910]

I am working on a dyno proven 587hp 427 Mark IV. It has a solid roller cam which is attached to a Reher Morrison top end. Roughly 11:1 compression. Spins 7000rpm.

It has a Holley 80804 850 HP carb on it. It idles perfect but is incredibly rich. When idling, if you mash the throttle, or even give it a quick 1/2 throttle shot, it goes flat and almost dies before picking up and shooting a black plume of smoke out the exhaust. Also, if driven at low rpm at operating temperature (165 deg), within 10 blocks the engine will start dying down at a stop light, and will become impossible to start

I have checked the timing. Locked out at 31 degrees. Tried 35degrees, zero change in response,

I made sure the floats in the carb are set properly, even went a little lower in the primary bowl due to it being so rich.

I did not change the jets as anything I have read about stumbling or bog does not point to jets. It mostly talks about accelerator pump or the pump nozzle.

Because of the plume of black smoke, I backed off on the accelerator pump adjustment to see if a delayed shot of fuel would help. It did not.

I did not have any pump nozzles to try and see if that would help.

The vehicle is desired to be driven as a casual driver, but it has this race themed carb on it. The owner wants me to put a 0-9380 850 DP on, with hopes that it's street friendly setup will cure the stutter in throttle response.

My problem is that everything I have read tells me the engine is going lean, when the black smoke, and the smell of my clothes tells me the car is running rich rich rich.

I can not hook an A/F meter to this vehicle unfortunately

I also changed the oil and it smelled very strong of gasoline.

Can someone please advise me on what to do? If there are any further questions, please ask them if they will help this situation.

[Wrenchbender Ret]

Sounds like the power valve is leaking.

George

[Getter-Done]

X2 on the power valve.
The Quick fuel power valves is what I had better luck with.
The don't blowout with the least little backfire.
Here's some from Jegs.

Link:https://www.jegs.com/p/Quick-Fuel/Qu...45236/10002/-1









.

[AussieinNC]

1/ Power valves bad...quick trip to auto store for some cheapy ones...if that fixes it, order Quick Fuel units from Jegs...flow values on existing units must match replacements
2/ Float cracked and filling with fuel
3/ Fuel pressure too high

[raceman6135]

All good info so far in the above replies. I'd also check:

-- where are the idle mixture screws set? That carburetor will have 4-corner idle mixture adjustment capability, so it's possible those need to be leaned. A good baseline for that list number is 3/4 of a turn from lightly seated i.e. tighten them (clockwise) until they just stop, then loosen them (counterclockwise) 3/4 of a turn. That should get you in the ballpark.

-- has the idle speed been adjusted so high that the fuel transfer slots are being exposed a great deal? If so, you likely need to idle bypass valve so that the idle speed screw can be reduced. "Classic" Holley double-pumper carbs do not have the idle bypass valve feature, so not everyone is familiar that it is there on this list number carb.

-- that carb has a screw on the secondary side that adjusts the position of the secondary throttle blades. If that is incorrectly adjusted, the secondary throttle blades may be open too far which will mess with the richness / leanness of the idle mixture.

Along with the other checks / adjustments mentioned by others, get my suggestions checked out and then see where you are.

That Holley also has the ability to adjust the air bleeds (both idle and main/high speed), but that's getting into fairly advanced tuning that, if done, must come AFTER all preliminary settings have been optimized.

[69GMC910]

Thank you all for your input so far! I’m going to start with the power valves first as the engine did use to run excellent, but has become virtually undriveable.

I’ll report back!