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Lean idle mixture on Holley

67 B-body

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Has anyone else experienced a lean idle mixture on a Holley DP carb?
I can't seem to get mine rich enough at idle...... My carb is older, so it only has idle mixture screws on the front metering plate, and the engine wont idle without the screws being 5 1/2 turns out! At this point, I believe it is maxed out and any further turning would do nothing. Spraying carb cleaner through the idle screw ports "with screws removed" shows cleaner coming out of the idle transfer slots.... The throttle blades are not open past the transfer slots.... The rear set of blades seem to be in the correct position at idle....
Before adding the 50cc pump, it would stumble at first throttle if you hit it quickly. That is now resolved... I added two sizes larger jets front and back to fix a little lean condition cruising and WOT... If I hit the accel pump arm at idle, it picks up RPM indicating a lean mixture... Strangest damn thing I ever seen....:angry7:
Other than idle mixture, it works like a champ! Very crisp, strong pulling, doesn't lean out at top RPM anymore.....
 
i believe you need to richen up your primay jets 1st then play with your idle mixture screws from there. thats how i do mine.
 
i believe you need to richen up your primay jets 1st then play with your idle mixture screws from there. thats how i do mine.
Well,,, I did just jump two sizes from where I was last summer....I went to 82 front and 88 rears with power valve plugged in the rear. The squirters are tube type #35, and the 50cc pump I previously described.
Do you think an 850 DP would need more jet than that? I have an entire set from 80 to 90 to play with....
 
Well,,, I did just jump two sizes from where I was last summer....I went to 82 front and 88 rears with power valve plugged in the rear. The squirters are tube type #35, and the 50cc pump I previously described.
Do you think an 850 DP would need more jet than that? I have an entire set from 80 to 90 to play with....

are you running a A/F METER?

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WHAT'S YOUR IDLE A/F readings?
 
No expensive A/F wide band meter...... All I know is that it's for sure lean, because hitting the pump arm at idle when it starts slowing down / stumbling, it will immediately jump in RPM...
The idle mixture screws should be about 3 turns in from where they are too...
 
Does it have adjustable airbleeds. If not maybe change to billet metering blocks that have them.Then close up the airbleeds to fatten it up.
 
Does it have adjustable airbleeds. If not maybe change to billet metering blocks that have them.Then close up the airbleeds to fatten it up.
I considered billet metering plates,,,, just getting allot of cash invested into this carb now, and start thinking to myself that I might have been further ahead buying a used Dominator and using the 4500 to 4150 adapter plate.
I just never tuned a Holley that was SO lean at idle before...???

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I should be able to mimic the adjustable air bleeds by covering up the air bleed holes and the mixture should go fat right??
 
go 86 primary and 89 secondary. i play with these pretty often.
 

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I thought the rule of thumb is to go 6 to 8 sizes larger on the rear when the power valve is plugged?

not necessarily. you need to get your idle problem sorted out 1st/
dont worry about secondaries yet. you really need to get a dual O2 meter/datalogger.
 
not necessarily. you need to get your idle problem sorted out 1st/
dont worry about secondaries yet. you really need to get a dual O2 meter/datalogger.

Correct,,, the idle problem needs sorted out.... My question is if anyone else has had troubles getting enough fuel through the idle mixture circuit to accomplish this? I already know it's extremely lean without the meters sniffing, because the RPM picks up when I hit the pump arm... If it were running anything BUT lean, it wouldn't pick up RPM with a shot from the accel pump....
I guess I'll just buy a set of billet metering blocks and try it.....
 
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