Holley 4150 Fuel sequencing

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AlV

AlV

Crabs in a barrel
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Hi FABO, I've been tweaking the carb on my Dart and want to better understand the sequencing of how and when fuel is delivered through the range. I drafted a simple and crude Diagram that depicts in general what I think is happening. Am I off? Does anyone have a better diagram?

holley 4150.JPG
 
Re thinking the presentation I've update the diagram to better show the components, and transition points.
I wanted to call out that the "Idle circuit" "Power Valve" and "Accel Pump" are working throughout the range starting at the transition from idle to primary.

4150 2.JPG
 
Crude but effective for starting the conversion.
The top arrow depicting the power valve is not accurate. The power valve activates when the vacuum is low. A PV rated at 6.5 will open up when the vacuum drops to that level, 6.5.

The idle arrows belong with the primary arrrow. The circuit is feed from the primary jets. Once you step on the gas pedal, the blades open up exposing the primary run slots in the primary barrels.

What is the running/tuning issue?
 
rumblefish360 said:
Crude but effective for starting the conversion.
The top arrow depicting the power valve is not accurate. The power valve activates when the vacuum is low. A PV rated at 6.5 will open up when the vacuum drops to that level, 6.5.

The idle arrows belong with the primary arrrow. The circuit is feed from the primary jets. Once you step on the gas pedal, the blades open up exposing the primary run slots in the primary barrels.

What is the running/tuning issue?
Click to expand...
Thanks Rumble.
I was getting a nasty Bog/hesitation like a stall on hard acceleration. This occurred from a standing start or from a roll. Basically, If I give it a goose it would whined up and go silent (waaaaah...zilch) falling on it's face. BUT, If I lift off the throttle power would come back and I could get into it again. I felt like it was starving for fuel but didn't know exactly where this was happening. This started me on the path of understanding the fuel integration sequence.

At first I though it was an issue transitioning off idle bringing in the primaries but after some experimentation I've come to the realization the issue was occurring on the transition after the primary as I was bringing in the secondaries.

I was able to get it pretty dang good by making the following adjustments:
  1. slightly increasing the float level in the Primary bowl just above the bottom of the sight hole to have a little more fuel in the pot.
  2. turned the fuel mixture screws on the metering block out two turns from bottom to richen it a bit.
  3. moved the accelerator pump cam to the first position which shortened the squirt duration but brought more fuel in the Primaries sooner.
All of this has given me the incentive to better understand how fuel supply is managed in the carb.

My particulars:
  • 69 340 .40 over (Call it 9.5:1) with stock Xheads and Valvetrain with hydro lifters
  • Comp xe275HL cam
  • Eddi Performer intake
  • Holley 670 Street avenger
  • MSD 6a with a probillet distributer plugs gapped at .035
  • Timing 20 initial and 35 total.
  • Park idles at 1050, 800 in drive
  • 14 inches of vacuum
  • Stock HP manifolds to TTI 2.5 exhaust
Thanks
AlV
 
Last edited:
Well, you just did the first 3 things I would have suggested but ....

A book by Mike Urich, HP books, Holley carb handbook covering the 4150 & 4160 models covers tuning and repair. This is a good book to have on the shelf.
 
rumblefish360 said:
Well, you just did the first 3 things I would have suggested but ....

A book by Mike Urich, HP books, Holley carb handbook covering the 4150 & 4160 models covers tuning and repair. This is a good book to have on the shelf.
Click to expand...
Thanks! Amazon here I come B)
 
Those street avengers are calibrated way lean from the factory. I had a hell of a time tuning out the bog in my 670 SA on my 340. The only real way to do it is fatten up the IFRs, which requires some drilling.
 
mopowers said:
Those street avengers are calibrated way lean from the factory. I had a hell of a time tuning out the bog in my 670 SA on my 340. The only real way to do it is fatten up the IFRs, which requires some drilling.
Click to expand...
What size did you drill out too!
 
AlV said:
What size did you drill out too!
Click to expand...

I drilled and tapped them for adjustable IFRs. I believe they were like .025" stock, which is too small for a hotrod motor. With IFRs so small, you end up opening the IM screws way too far, which makes the idle AFR way too fat to achieve an acceptable transition AFR. I think I ended up with .031"-ish.

Higher float setting, fuel pressure, larger squirter and cam, etc may also help a tad, but are sort of bandaids for fixing a Holley Street Avenger bog IMO. Open up those IFRs.
 
Hate to ask, but what is a IFR & IM screws?
 
The idle circuit pulls fuel from the main well which is fed by the main jet.

There is some overlap in the idle and primary transition period.
 
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