Holley tuning help please

[krowbar]

I am in need of a tuning guide or web link for Holley Double Pump tuning. I need to understand the circuits a little better to diagnose my problems.

 

[HEMI-ITIS]

Here'a a start to look at. What is the issue with your carb?? Plenty of guys here with knowlege:icon_thumright:

 

[Meep-Meep]

The Holey web site probably has something. I know the books do. Or, as stated, spill the beans on your problem.

 

[krowbar]

I have a 850 DP on my 440. .484 purple cam. Torker intake. 2500 stall converter. In park when I romp on it I have a flat spot past idle. Cruising flat spot/hesitation when I get into it. I advanced the timing by ear and vacuum gauge. changed primary acc. pump cam and it got a little better.Didn't drive it after changes yet. A/F ratio at idle is 14.2. Vacuum @550 rpm is 6. @750 its 10. @ 1000 its 12.5. I have a 6.5 power valve. Thinking I need a lower # power valve?

 

[Meep-Meep]

What is the timing? And do you know what your compression is? Cranking cylinder pressure? Just trying to get an idea of the setup. Carbs like velocity, and with the improper setup that goes out the window. Do you have access to another carb like a 750 vac secondary? It's a fact that a too large carb will run leaner when put in the wrong application because it's much easier to move air through a venturi. Get your basic settings correct (lots of initial timing) and if the problem persists try another carb. My thought is if you have to drastically alter a carb for an application you have the wrong carb. Example: Throwing a ton of pump shot at it to make the bog go away is really masking a problem.

 

[krowbar]

I have a 770 street avenger. The problem with changing carbs is the PO must have stripped the intake threads and put bigger thread inserts in. I had to wallow out the holes on the New baseplate for the 850. Don't want to jack with that on the NEW street avenger. I may have too big of main jets also. I have 82 primary, 80 secondary jets. I've dumped too much $$ into this carb to give up yet. I like to know how and be able to work on my vehicles. I know alot and forgot alot,but I definitely don't know it all.

 

[Gpuller]

Surprised it will even idle at 550 RPM. My 440 has the same cam but Torker 2 intake and 750. Like Meep said do you know where your at with timing. Have to get the timing squared up first before carb tuning. I'm running 25deg of initial timing.

 

[krowbar]

I will try to check the timing tonight. Quik reference;what RPM is timing set at? Not sure how much to give it either. what's a reasonable starting point for initial timing. My C.R. is pretty low 9's IIRC.

 

[hunt2elk]

I'm not a Holley pro by any stretch of the imagination, but we ended up with the 770 Street Avengers on both my current motors. One is 489 hp 440 and the other is a 522hp 451. Both carbs have 72 primarys and 75 secondarys.

 

[krowbar]

Timing is now @ 30° initial and 60° all in. That seems like alot. Mixture screws out 2 1/2 turns. curb idle about 750. In gear about 550. Still has bog about mid throttle when I stomp it in park. I'm using a cheap Harbor Freight timing light w/advance dial. Match initial timing mark w/ another timing light for comparison...........???

 

[lewtot184]

you'll never figure the carb out until you learn to figure the timing out. 60 degrees total sounds like your checking the total timing with a vacuum advance hooked up. just arbitrarily raising the initial won't work. initial has to compliment the centrifugal timing in the distributor you need to know how many centrifugal degrees are in the distributor. find a competent person locally who can put put eyes and hands on what your doing so you can get a good base line on the ignition. a carb can't be properly tuned if there are any ignition problems. the carb may not be the big problem. the carb's far from being too big. sometimes these internet websites are the worst places to go for problem solving.

 

[69Runner]

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.

 

[krowbar]

you'll never figure the carb out until you learn to figure the timing out. 60 degrees total sounds like your checking the total timing with a vacuum advance hooked up. just arbitrarily raising the initial won't work. initial has to compliment the centrifugal timing in the distributor you need to know how many centrifugal degrees are in the distributor. find a competent person locally who can put put eyes and hands on what your doing so you can get a good base line on the ignition. a carb can't be properly tuned if there are any ignition problems. the carb may not be the big problem. the carb's far from being too big. sometimes these internet websites are the worst places to go for problem solving.

Vacuum was disconnected.

 

[lewtot184]

Vacuum was disconnected.

then that should tell you that there is 30 crank degrees in the distributor. what distributor are you using?

 

[krowbar]

Original dual point style but it was converted to electronic. Have MSD 6A and blaster coil. No ballast resistor.

 

[lewtot184]

Original dual point style but it was converted to electronic. Have MSD 6A and blaster coil. No ballast resistor.

you need to call FBO at 1-541-942-5920. they make some limiter plates to take degrees out of the distributor. you need to take 10-12 crank degrees out. this isn't a difficult task. the only problem may be the prestolite distributor. i've used FBO stuff before and have found them to be a good vendor. i'm not a MSD fan but with already having the 6al you may want to compliment it with their distributor. the MSD distributors are basically gm/delco design and very easy to tune. make sure you have good clean grounds! what heads and spark plugs are you using? after this is all sorted out then the carb can be tuned.

on the carb i'd recommend 78 primary jets and 80 secondary jets, retaining the power valves. i don't like big squirters. for something your driving they are just plain unnecessary nonsense. a .028" squirter in the front with a blue 427 pump cam will work nicely. a .031" squirter with a red 240 cam in the back. make sure both pumps are 30cc, no big stuff. power valves can be changed from the original 6.5 to a 4.5 if the need arises.

 

[krowbar]

Iron heads ported and polished w/ S.S. 2.14 intake 1.88 exhaust valves. Mopar forged crank. 2" super comp headers.Torker 2 intake. Forged pistons. 1.5 rockers w/ double springs. Autolite 85 plugs.

 

[Meep-Meep]

Timing is now @ 30° initial and 60° all in. That seems like alot. Mixture screws out 2 1/2 turns. curb idle about 750. In gear about 550. Still has bog about mid throttle when I stomp it in park. I'm using a cheap Harbor Freight timing light w/advance dial. Match initial timing mark w/ another timing light for comparison...........???

Setting the timing to 30 initial and not limiting the mechanical will give you the 60 that you see - or some really high number. What you must do is limit the mech advance inside the dizzy. On the factory Chrysler distributor I tack welded some 1/16" welding rod across the slot so that the pegs on the weights stop on those rather than the end of the slot. If I recall I reduced the travel by about .200" to allow 18 initial AND keep 31 total (426 hemi application). Wedge should get 36-38 total, and in your case with 9.0:1 CR or less, you will need at least 20 initial. Your real problem is what I suspected - that cam must go. Swap it with the .455" / 272 MoPar cam. I have two engines running that cam, one with 9.5:1 and one with 10.1:1. Seems great and pulls 12" vac at idle.

 

[lewtot184]

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

 

[krowbar]

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?