Ford Mustang Forum banner
1 - 11 of 11 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter · #1 ·
Hello;
I have posted before about my 1968 mustang coupe with idle problems. It has a 1967 289 with unknown C4 auto with edelbrock performer intake, holley avenger 600 cfm, hooker headers & from what my mechanic tells me an agressive cam. Not sure what cam specs are, was in when I bought it. Anyway, that problem I have been fighting & now my mechanic, is that it stalls when shift in gear at 900 rpm park idle. Other than that it runs great under normal acceleration & at WOT. I have checked for vacuum leaks & so has my mechanic. I am only getting about 8 vacuum with timing set to 12 BTDC. I have tuned carb. & now the mechanic has really dialed it in with no change. When we set the idle to where it runs in D it jumps to around 1500 in P. My mechanic is leaning toward my needing approx. 2500 stall torque converter to eliminate the problem (B&M holeshot 2400). What does everyone think? Agree or disagree? Have read arguements both ways, does anyone know? This is for my son when he graduates from Marine Corp. boot camp Nov. 30. I am running out of time as I still need to sand & paint after fixing this problem. It will be a daily driver for him after his training & will have to handle some driving on base at 5 mph. Thanks for any & all input!
 

·
Registered
Joined
·
491 Posts
Do you have a spacer between the carb and intake mounting base?
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #3 ·
No I don't have a spacer. There wasn't one on it when I bought it & my mechanic told me that it wouldn't help. What are your thoughts on this? Thanks for the reply!
 

·
Registered
Joined
·
582 Posts
If a stall converter fixes your problem, your camshaft is nowhere near being a good daily driver cam. I will keep my fingers crossed that you can find a vacuum leak somewhere (carb base, A/T line, power brake booster line, etc). Stall converters for a daily driver will most likely lead to your hatin' life.
Best,
Al
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #5 ·
Al;
Cam could be too agressive for street. Can anyone think of something it could be besides a vacuum leak or is my mechanic right & I need stall converter? When we set the idle high enough for engine to idle in D & then shift to P it jumps to about 1500 rpm or more. If set to 800-1000 in P dies when shift to D. Runs great at normal accel. or WOT & cruising. Could this be caused by Holley carb. needs different jets because of the cam or possibly require secondary throttle plate adjustment? Could it be a problem with the new pertronix ign. or coil, I ran a new wire from ignition switch to coil for 12v. Just trying to come up with some other fix than a higher stall converter. I know engine basics, but when it comes to performance upgrades I have no experience, have only worked on stock engines. Thanks for any & all help! I really want to get this fixed for my son's grad. from Marine boot camp!


1968 Mustang coupe w/1967 289
c4 auto (unknown year)
was 2bl Now 4bl edelbrock performer intake
Holley 4bl street carb. 600cfm vac sec. #80457S (new)
was single exhaust now dual w/hooker headers
Pertronix Ignitor III with Flame-Thrower III coil (New)
Accel super stock 8mm wires (new)
 

·
Registered
Joined
·
491 Posts
You are fighting the exact same problem I had. If you will go out, open the hood, and run your fingers around and under the holley baseplate you will see that it overhangs the edelbrock mounting pad, alot, which creates a vacuum leak. Even though there is a gasket under there it is not sandwiched enough to cover the vacuum passages adequately to prevent a leak. You can put a squarebore spacer under the carb and the vacuum leak will go away. When I installed a spacer, some of my problems went away because my vacuum leak went away, then I had to retune the carb.

Now the mechanic, while he has the carb off, will have to adjust the carb so that the primary transition slots are only exposed by about .020 of an inch, and set the secondary the same. Then bolt it on and tune, should go better. Right now he has the curb idle adjusted so high that too much of the transition slots are exposed, just to get it to idle, because of your vacuum leak. Once this is straighted out you may end up with an off idle bog which is hard to tune out on this carb, which is very frustrating.

With that being said the street avenger carb is an emissions carb. The terms "emissions" and "hot rod" should never be used in the same sentence. I don't know how funding comes into the mix here, but if funding is not a factor I would remove the holley, install an edelbrock 600 and be done with it. You don't need a spacer, which is a band aid for a problem created by the holley carb/edelbrock intake. The edelbrock also has a much better idle circuit and is more tunable than the holley, especially when running a C4 tranny. You wouldn't need your mechanic, just remove the holley, install the edelbrock and set curb idle and idle mix and be done with it.

When I ran into this same problem, I borrowed an edelbrock 600 from a buddy, bolted it on and all of my problems dissapeared. There are lots of forums that address major problems with the street avenger series. Being an emissions carb it is tuned very lean which is not good for a hot rod. I am including an article I used for tuning my avenger which helped immensly, got it close but I never got it right and retired it. Print this out and hand it to your mechanic, and if he doesn't agree or will not listen, find another mechanic. If the mechanic is not a hot rodder he is not aware of these problems. If you get this problem straightened out you may not need a stall converter. A stall converter, until you have your idle problems fixed is a very expensive band aid for a carb problem. Now if you do have a very healthy cam its possible you may have to go that route, but I have a buddy with a 66 that has a cam that rocks like a promod and he can idle his motor down to 700 rpm curb idle. He is also running an edelbrock carb/edelbrock intake combo, no vacuum leak.

http://www.corvette-restoration.com/resources/technical_papers/Holley_Carb_Tuning.pdf

Also, thank your son for his service, I am a 2 tour combat veteran, I understand where he is coming from.
 

·
Registered
Joined
·
582 Posts
Ranger is on to something with advice about replacing the carb. I have no experience with the Avenger series carbs,but am a big fan of the oh so simple and reliable Edelbrock carb. With your present setup and the tranny in "park" set the idle as low as possible. If that set is at or under 500 rpm, then you will have to locate the air leak that is present somewhere. Just not much else it could be.
Best
Al
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #8 ·
Ranger1;
My edelbrock performer intake is a square bore intake #2121 & so is my Holley 4160 street avenger #08457S so I do not think I need the spacer. Evidently some of the edelbrock performer intakes must have been spread bore? LMK
Al;
I can only adjust the idle down to about 750-800 in park. Would not stay running at 500 or under.
Thanks for the replys, but it still looks like I am looking at something else. Ranger1 I will go to the shop tomorrow & check between intake & carb for leak though. Any other solutions?
 

·
Registered
Joined
·
491 Posts
You are correct that your intake is a squarebore, same intake I have. I could spray around my carb but could not detect a leak simply because my idle was so high, just like yours. Then on this very forum, a kind gentleman by the name of Paul Stevens told me my problem. I followed his advice, bought a 1" phenolic spacer and my vacuum leak dissapeared. Then I could actually idle down and my air fuel mixture screws actually did something.

Both Holley and Edelbrock may squarebore carbs but the width/depth of the baseplates are different, butterfly centerlines are the same and each carb will bolt onto each intake. Holley makes the Wieand intake with a wider mounting flange to mate with the Holley carb, and naturally Edelbrock matches width of their intake to fit their carbs. Both carbs are virtually the same depth of measure. You can mount an Edelbrock carb on a Wieand intake with no leaks, but mounting the Holley on the Edelbrock intake creates leaks, been there, done that, got the T-shirt.

Try this short test tomorrow. Start the car, let it warm up....then cup your hands as tight across the airhorn of the carb as you possibly can. If the motor stalls you do not have a vacuum leak....but if the motor continues to run you have a vacuum leak. Think about it....if you are cutting off the flow of air with your hands then where is the air coming from to let the motor continue to run...air leak at the baseplate?

I have an Autolite 4100 on my car now and still have to run a spacer because of the width of the carb vs the width of the intake mounting base. I just measured my adapter, and on both sides of the carb the adapter overhangs the intake mounting base by 1/2". If your avenger is like mine, and should be, on the passenger side, rear there is a vacuum fitting I think for power brakes. The slot in the carb baseplate runs out to within 1/4" of the carb mounting base. This means there is 1/4" of vacuum slot that is not sandwiched between gasket and intake without an adapter.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #10 ·
I went to the shop today & checked my carb mount to intake. I have the newer Holley street #80457S not the street avenger #80670. Sorry about that, I did call it an avenger earlier in the post. I do not have any vacuum fittings on the sides where the overhang is. My mechanic did tell me that I should have the 1/4" spacer under the Holley instead of the thin one that came with it, so I got that today. My problem is much different than yours was, in that I can idle down to about 600 with no problem & my idle mixture screws are working fine. What my mechanic has determined & verified with his transmission guy is that the cam that was installed is very lopey & too much for my setup. So, it looks like I have to go with a higher stall torque converter. Not knowing what the cam specs are, it is a toss up between 2400 & 2800 stall.
Do you have any experience with different brands of torque converters. I have seen B&M holeshot mentioned in forums, but not any of the other brands. The local speed shop is telling me that a Boss Hog would be just as good for my application as the B&M and for a lot less money. I am looking for mainly streetability with an occasional show off.
If anyone has any reccomendations from experience I would greatly appeciate it. I will probably order one later today or in the morning as soon as my mechanic verifies if the tranny is 24 or 26 spline, as we don't know what work has been done to it. Thank you very much for your help so far Ranger1 & Al!!!!
 

·
Registered
Joined
·
491 Posts
I would try doing a google search for Boss Hog torque converter reviews before buying. I've read on forums that certain torque converters have a high failure rate.......not sure which ones as I've never been in the market for one so don't remember the specifics. Glad you're on the right track and hope you get the car like you want it.
 
1 - 11 of 11 Posts
Top