670 holley lean off idle stumble

[Knebel]

hi all! I need someone who knows holleys. I have a 670cfm street avenger which... idles 100 times better than my carter and runs pretty good down the street. I just have this off idle lean spot when I push the throttle a little harder. Idles at about 13.5 to 14:1 afr and when i hit the throttle hard it goes to 16...17...18...20:1 afr.

I have 65 primary jets, orange pump cam, upped the squirter from 31 to 35 but that seemes to have done nothing. I also get an instant pump shot. I Lready have bent the pumparm a little so it fully runs on the cam, seems to be a common problem...When I slowly roll in the throttle i dont see an afr change on my meter and i can take off slow but without the leanspot. I need the car tomorrow and have to get rid of that flatspot!

 

[commando1]

It is all in the accelorator pump 90% of the time.
There should be zero slack between the screw and the arm at idle
andat full throttle the arm should still not bottom out.
How does yours look?

 

[Knebel]

Ok, the pump cam was in hole 2 and the pumparm was riding on the flat spot of the cam. Changed it to hole 1 and its A LOT better. Afr goes down now to 12.5:1when i take off. Now, that super lean off idle cruise...

I accelerate, afr goes from 13.5 to 12.5ish due to the pump, then it goes up and stays at about 16:1

I changed the primary jets from 65 to 70 And it seems to be gone but now when i get on the throttle a little harder it goes down to 11 sometimes 10:1 and stays there until speed picked up. Thats way too rich. I pull about 12 to 13" vacuum at idle and have a 5.5 power valve.

Should i go down on the jets to 68 (since 65 created 16 or 17:1) Sorry, holley is pretty new to me but hey, it runs better untuned than the carter afb tuned.

 

[C Body Bob]

Have you installed a Performer RPM intake & running a stock cam?

 

[70bigblockdodge]

Most likely the power valve. My 2 cents. On a Holley the main jets control cruise and power valve fattens it when vacuum drops. What is cruise AF with 70 jets the 68s may fix it if your cruise is 14.

 

[Knebel]

Supposedly the engine has a "cam" in it. Thats what i know from the previous owner. theres a performer intake on it, yes. No lopey idle or anytanything. I will go for a drive and check the cruise.

70bigblockdodge, you mean the power valve restrictions?

 

[C Body Bob]

Vacuum seems a little low. Done a compression test. Also see if vacuum gauge pulses or fluctuates. May need a valve job. Anyway none of that should cause a stumble off idle. That large plenum intake will. May try a thin 4 hole spacer. If you have hood clearance. Happy tuning

 

[C Body Bob]

BTW a regular performer should be fine on a stock or mild engine. The RPM has a weak signal down low on a stock engine. Hard to completely overcome that. Run her rich

 

[Knebel]

I do have that performer with the devided plenum. 1" four hole spacer too. I...yeah, i curious why the vacuum is that low too, its in gear and I run 18° initial plus vacuum advance. So about 30° at idle. Anything under and the vacuum is gone and the car dosent idle Right. Total is 35°ish....hard to see. I think the engine is fairly worn and the vacuum gauge twitches a little, occasionally fluctuates about 2". Should have seen that with the old carb... fluctuated sometimes 5" absolutely random. With the holley now i have set the idle and the engine sounds way way healthier now.

Do you know at which speed/rpm the main jets are active?

 

[C Body Bob]

Hum....18 initial & 30 at idle. Sure about that ?

 

[Knebel]

Yeah, I kid you not. And i made sure that the balancer didnt slip either. I even found timing specs for my 78 360 which calls for 22° initial. It idles just fine like that, dosent even kick back (at 40ish it stars having a hard time) believe me, i tried it up and down. 12° sounds, idles and drives like crap.

 

[C Body Bob]

Ok I don't know your combination, but thinking initial 6-10 vacuum advanced unhooked & plugged. Hooked back up & rev to 2000 & maybe 18-22 & 32-34 around 3000 make sir you don't have the dizzy hooked full time. Look to see if the valve cover & timing cover gasket look new. Will be a good clue as to a recent cam change.

 

[C Body Bob]

Ok I don't know your combination, but thinking initial 6-10 vacuum advanced unhooked & plugged. Hooked back up & rev to 2000 & maybe 18-22 & 32-34 around 3000 make sure you don't have the dizzy hooked full time. Look to see if the valve cover & timing cover gasket look new. Will be a good clue as to a recent cam change.

 

[Knebel]

Ok I don't know your combination, but thinking initial 6-10 vacuum advanced unhooked & plugged. Hooked back up & rev to 2000 & maybe 18-22 & 32-34 around 3000 make sure you don't have the dizzy hooked full time. Look to see if the valve cover & timing cover gasket look new. Will be a good clue as to a recent cam change.

It wo t run like that. 6-10 initial with advance hooked to ported vacuum gives me like..5" of vacuum and i have to open the throttle blades too much to make it idle. I have spend A LOT of time sorting that timing issue out tho

 

[C Body Bob]

Either your balancer has slipped giving incorrect timing marks. Or it's jumped timing or their was a cam change & the gears where not lined up properly. You are compensating for it with all that timing & advance. You might want to find true TDC. Just to see exactly where you are at with the timing.

 

[Knebel]

Either your balancer has slipped giving incorrect timing marks. Or it's jumped timing or their was a cam change & the gears where not lined up properly. You are compensating for it with all that timing & advance. You might want to find true TDC. Just to see exactly where you are at with the timing.

Been there, done that. Tdc lines up with the mark on the balancer...

 

[C Body Bob]

Been there, done that. Tdc lines up with the mark on the balancer...

Did you get the slack out of the chain & after you found TDC where was the rotor pointing

 

[Knebel]

I think i get to understand that thing a lil better...

Had the secondaries open too much and that messed with the idle a bit So that took some time to get the right balance.

Now i have about 14:1 idling and easing in from a stop i get 15.5:1, same cruising with the the throttle cracked just a bit. When i get on it harder from a stop my afr gauge flips out cause it goes way rich and under 11:1. With a fairly moderate normal takeoff the afr gauge blips about 1 point...when getting on it while moving it goes way rich too. I have a 31 squirter now and the orange cam. I only have a 35 squirter and this is too much.. thinking i might need a 28 or 29 squirter. Or go for a less aggressive pumpcam

Edit:i put 68 jets in the primaries and 70s in the secondaries

 

[Knebel]

Here are some AFR figuers i have.

Primary jets 68
secondary jets 70
Pump nozzle 31
pump cam orange
Power valve 5.5" (four door)
Vacuum at idle in gear 12" to 13"
Idle speed P-850 D-800 to 825ish
Idle AFR 14.5:1
Light off idle acceleration goes down to 11:1 then immideately to: Cruise just off idle between 14.5 and 15.5:1
Cruise at 45mph 14:1
Heavier acceleration from about 2/3 to wot is 11:1 regardless of from idle or moving at 35mph

WOT was 11:1 and even blipped town into the 10:1 range once.

The fury drives and feels like i just bolted on 100hp... wow..i am impressed. When i floored it from 35mph and the secondaries opened it felt like the car got a HUGE powerkick...wow.

Now my concern is, how do I tune the richness out off the acceleration. I can probably put the 65 jets back in the front and the 68s back in the seconds which will lean out the high speed cruise some more but how do i get the power mode leaner without having to modify the metering block to accept pvr jets? I am aiming more toward 12.8:1 wot and maybe a little leaner around 13.5 in power mode when the PV opens.

Commando1, i read somwhere that you know holleys ☺ and i also did the pump arm adjustment hand have a 28 squirter and pink cam on the way. Any ideas?

 

[commando1]

Commando1, i read somwhere that you know holleys ☺ and i also did the pump arm adjustment hand have a 28 squirter and pink cam on the way. Any ideas?

Are you kidding? I'm learning more stuff off of you...