Holley tuning help please

[Meep-Meep]

every .015" reduction in the slot length reduces mech advance 1 distributor degree (2 crank degrees).

Good info, but where were you when I was figuring this out!? :hello2:

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I was told (by the previous owner) that there is a Allen head screw inside the vacuum advance that he cranked up to raise the timing. This guy raced this car. Basically everything is the same as he had it. It sat for MANY years. The only things I changed to ALTER his setup was bigger primary jets because the plugs looked kinda lean. Now that I have the A/F ratio gauge, it looks fat. I think I will go back to the #80 that was in originally. Maybe lower depending on the gauge readings. Any thoughts on that screw in the vacuum advance?


Screw in vac advance is only for the vac advance. Has nothing to do with the mech setup as I discussed. You should rn a vac advance on the ported port and a god starting point is to add 10 degrees with full vacuum applied to the can. Use a vac pump or temporarily hook to manifold source to set and verify.

 

[lewtot184]

I was told (by the previous owner) that there is a Allen head screw inside the vacuum advance that he cranked up to raise the timing. This guy raced this car. Basically everything is the same as he had it. It sat for MANY years. The only things I changed to ALTER his setup was bigger primary jets because the plugs looked kinda lean. Now that I have the A/F ratio gauge, it looks fat. I think I will go back to the #80 that was in originally. Maybe lower depending on the gauge readings. Any thoughts on that screw in the vacuum advance?

all the screw does is raise or lower the amount of vacuum needed to pull the vacuum advance in. i'm also thinking the prestolite distributors don't have the adjustment but i haven't fool with them in years and could be wrong.

 

[Meep-Meep]

all the screw does is raise or lower the amount of vacuum needed to pull the vacuum advance in. i'm also thinking the prestolite distributors don't have the adjustment but i haven't fool with them in years and could be wrong.

Old prestolites have a removable Vac port and that allows access to spring for shims or spacer.

 

[krowbar]

Changed back to 80 jets. Still stumbles while cruising when I throttle it. A/F is @ mid 13's while cruising 2000- 2500 rpm. When I throttle it A/F goes to 16's when it stumbles. Is it the nature of the beast with this cam and intake? Is it still a timing issue?? More carb tuning? Pump shot seems fine.

 

[Meep-Meep]

Well stumble seems to be a lean condition. That cam is killing you and the big carb isn't helping the lack of velocity. Remember, it's easier to move air through a venturi than to get fuel out of the bowl through the emulsion curcuit. A smaller carb will help immensely.

 

[Icecobra]

You mentioned you turned the adjustment screws out to 2 and a half turns. Use a vacuum gauge to determine the proper in or out of the idle screws keeping in mind they are only idle mixture screws. But have an impact off idle how things are mixing. You want to set the screws by turn them in until the engine begins to stumble then back it out until you achieve max vacuum on a constant vacuum port. On mine I am about 16hg vacuum at idle and it takes adjusting both sides several times to get the highest hg reading.. Carburetor adjustments are mostly lead by vacuum since it is how a carb works dragging air through it...

 

[krowbar]

I would try the 770 street avenger but I would need a spread bore to spread bore adapter because of the screwed up manifold bolt pattern. Does anybody have adapters like that?

 

[Canyon707]

Talk to Ron at Performance Carb http://www.performancecarb.com/

 

[Meep-Meep]

Why not just pull the intake and repair the threads with a helicoil or timesert?

 

[krowbar]

I played hell getting that intake back on when I replace the valley pan. I wonder how JB weld or epoxy would work if I put 5/16 studs in the 3/8 helicoil and let it setup.

 

[Meep-Meep]

You can still heli-coil or timesert repair with the intake on. Just keep the chips out of the big hole. JB might work OK for carb studs. Try it. Worst case is you drill it out.

 

[Canyon707]

I am curious on how to determine the difference between a 2 circuit 1050 holly dominator and a three circuit. Any pics or info on how to determine ???

 

[lewtot184]

I am curious on how to determine the difference between a 2 circuit 1050 holly dominator and a three circuit. Any pics or info on how to determine ???

pretty sure a 2 circuit has 2 air bleeds per venturii and a 3 circuit has 3 bleeds per venturii.

 

[Bigal75]

pretty sure a 2 circuit has 2 air bleeds per venturii and a 3 circuit has 3 bleeds per venturii.

Pretty much - as well as a nozzle in the venturi (lower portion) can't miss it. I'm in the process of converting my 3 circuit 1050 to 2 circuit for street use.

Is the stumble at rpm or off idle?

 

[Bigal75]

how do your transfer slots look - dont touch your settings and flip the carb over - there should be about 0.020 of the transfer slot showing.

 

[Tempest 455]

The accelerator pump nozzle (shooter/squirter) is easy to change and they are numbered. Try different sizes to see if there is an effect on off-idle performance.

This.

Most off idle stumble (if timing is correct) is from a lean shot. Increase until stumble is gone.

 

[krowbar]

Pretty much - as well as a nozzle in the venturi (lower portion) can't miss it. I'm in the process of converting my 3 circuit 1050 to 2 circuit for street use.

Is the stumble at rpm or off idle?

The stumble isn't from the pump shot. It's a LITTLE farther up in the transition between the pump and the main. Maybe in the main.

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Pretty much - as well as a nozzle in the venturi (lower portion) can't miss it. I'm in the process of converting my 3 circuit 1050 to 2 circuit for street use.

Is the stumble at rpm or off idle?

The stumble isn't from the pump shot. It's a LITTLE farther up in the transition between the pump and the main. Maybe in the main.

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how do your transfer slots look - dont touch your settings and flip the carb over - there should be about 0.020 of the transfer slot showing.

I will have to check tonight. I pulled the 850 off the intake to measure the spacings on the 3/8" threaded inserts.
Has anyone tried the Percys base plate gaskets? My intake isn't planed very flat. Got a little warpage. I'm almost wondering if I had a small vacuum leak.

 

[Canyon707]

I got mine figured out. My 1050 is a 2 circuit. I took it apart and found some interesting numbers inside. my fron juts were 95 my rear jets were 98 and the power valves were 6.5 No wonder the car runs so rich and feels dead at the top end. I changed a few things 92 jets square and plugged the primary and secondary power valves. the powe valves addabout 10 jet sizes to the card so my A/F was reading correct RICH RICH. This was recommended to me by a race engine builder here that builds a lot of 440 motors. Won't be able to run it till the 8th of July due to Nascar and AMA races but I am open to any thoughts on this.
Thanks

 

[krowbar]

I got some 3/8" to 5/16" studs from O'reilley's. They are JUST long enough. Couldn't put the phenolic spacer on it,but I did get the 770 street avenger on. I had to adjust the mixture screws out a little. No more hesitation. I have to tig some 3/8 to 5/16 bolts together today so I can make longer studs for the phenolic spacer. I was getting too much heat soak bolting the 770 directly to the intake.

 

[66Satellite47]

krowbar, are you still running 60 total timing?