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Hi all,
Have a '69 Cutlass "S" with the original 350, 310hp with a 2 speed ST300. Previous owner put an Edelbrock intake and Holley 6500 double pumper carb with MSD ignition and HEI distributer. Issue I'm having is about 60 mph the car starts "tugging" or "pulling" under acceleration. I checked the timing at idle (600rpm) it was way advanced probably 35+ degrees brought it back to about 12deg. (the vacuum advance tube removed) Took her out for a test drive and its still pulling although the performance otherwise is much better. Any one have any notions as to what can be causing the issue?
Thanks!
Last edited by seabass; December 28th, 2021 at 03:15 PM.
You need to check your total advance curve, an advance timing light will allow this. There could be a lot of vacuum advance on a factory advance canister, like 30+ degrees. What octane gas are you running? Also the carb could be way out to lunch as well, compounding the issue.
Last edited by olds 307 and 403; December 28th, 2021 at 04:46 PM.
Good video.
Need a better description of the symptom.
Pulling = good as in pulling hard.
Pulling left to right isn't good,
Tugging is more related to towing a trailer or a brake hanging up.
Would Air/Fuel bog be more accurate?
100 Questions:
Does it happen at tip-in off idle or just at the top of 1st or 2nd gear towards WOT??
Is it an MSD or MSDL?
Is this a manual or electric choke 650 Holley?
Is the intake a single or dual plane?
What is the rear-end gear?
What is the fuel pressure?
What is the vac advance at idle(650-750 RPMs). You have it at 12° base + what is it plugged in?
What is the total advance and at what RPM is it all in for that total advance?
What's the curb idle vacuum signal(reading)?
Verify all 3 timing events. Read the spark plugs and exhaust tips and report back. White Black or Tan?
My guess is rich towards WOT. IMO wrong carb for the application. 650 Dbl pump is for a stick shift or high stall converter in a light car with low rear gears. You would likely be better with an AVS style carb. You might be able to get this Holley to run but you are tunning something that's starting off in left field.
Will probably have to get an advance light and check the timing at 3500rpm. Using premium 93 octane. I thought it could be the carb or the pump as well but figured timing was a good place to start.
Thanks I will have to check all these out, will take her on the highway and see if I can be more specific on the "bog". I know the the plugs were R43S, slight tan on them but did not look bad. The exhaust at the tip is slightly white.
Secondary pump nozzles aren’t your problem, neither is the octane, choke or most of the other stuff listed.
My bet is timing, HEI Module, fuel starvation or it’s going dead rich or lean due to jetting etc.
Are the bowl levels set correctly?
I’d start at verifying timing, installing a fuel pressure gauge of some sort and/or getting an air/fuel netter to somehow verify fuel supply at that speed.
Best of luck.
Secondary pump nozzles aren’t your problem, neither is the octane, choke or most of the other stuff listed.
My bet is timing, HEI Module, fuel starvation or it’s going dead rich or lean due to jetting etc.
Are the bowl levels set correctly?
I’d start at verifying timing, installing a fuel pressure gauge of some sort and/or getting an air/fuel netter to somehow verify fuel supply at that speed.
Best of luck.
I agree, he needs to verify timing first. I just wanted to make sure he wasn't trying 87, 93 should be more than adequate. I had the same issue at very low speeds with 9 to 1 compression trying 87 and needed to remove 10 degrees of vacuum advance. I went from a 30 degree vacuum advance to a 20 degree, fixed it. Trying unplugging the vacuum advance and plug the line, take for a test drive. See if it goes completely away. Most aftermarket vacuum advance have 20 degrees max with adjustment down to a couple of degrees.
Thank you everyone for the info, think I know what the problem is. I was told it had a Holley 650, after checking the serial numbers I have an 870 street fighter. Spoke with Holley tech support and this carb is way to big for this engine and its not getting enough air causing the surging at higher speeds. Got an advance timing light showing up today so I can correctly adjust the advance at least that will be something. Anyone want to buy a big *** Holley carb!
Yeah, a bit big but might be possible to get an acceptable tune on it. Mark usually recommends a 750 on a 350. Is it a vacuum secondary carb? FYI, there should be a number on a factory vacuum advance canister to tell you the degrees of advance. Who knows it could be a Chinese copy HEI which have a points curve, at least the one I have does. Good luck.
It is a vacuum secondary carb, no number on the vacuum canister. HEI does not have a brand on it so not sure where it came from. Did a spec out with Holley tech support and I have a 670 Browler carb on order, hopefully that should fix the problem.
The number is on the top of the arm under the cap. Also look for Delco on the ignition module. If no numbers, probably a Chinese knock off, which are Ok, it should have 20 degrees of vacuum advance and be adjustable. You will probably still need to tune the new carb, needs jets etc and a wideband. It may also be the wrong spring in the vacuum secondary if it is happening during secondary opening.
Thank you everyone for the info, think I know what the problem is. I was told it had a Holley 650, after checking the serial numbers I have an 870 street fighter. Spoke with Holley tech support and this carb is way to big for this engine and its not getting enough air causing the surging at higher speeds. They really told you that? WOW! What a line of total and complete bullshyt! Got an advance timing light showing up today so I can correctly adjust the advance at least that will be something. Anyone want to buy a big *** Holley carb!
Buying a new 670 won't automatically fix your porblem. If nothing eles you still need to get an AFR meter to check the jetting etc.
I've had issues with Holley tech for awhile now, mostly on the EFI side. However I'm convinced that 90% of them don't have a clue what they're talking about.
Sorry for the delay, Covid kicked my *** the last week. New carb has not come in yet but I removed the HEI cap no numbers on the advance weights, I did hook a manual vacuum pump onto the advance canister it did not hold vacuum or advance the weights so unless I'm doing it wrong its bad which would account for a lot. Current timing is 10 degrees at idle, 30 deg full advance at 3000 rpm. Pic attached of the distributer no brand or part number.
g the canister is bad
That looks like an aftermarket Chinese HEI. I would add another 4 to 8 degrees of advance. That is very little advance, especially without a working vacuum advance. You went from one extreme to the next. That pump should have moved the vacuum advance. Pick up a new vacuum advance canister for it.
Last edited by olds 307 and 403; January 6th, 2022 at 10:04 AM.
December 28th, 2021, 03:09 PM
