1acesmith

I'm inexperienced with timing/vac advance and have read a lot of posts so I apologize for asking a question that's probably been answered.........

I have a 72 Cutlass Supreme and I swapped in a 1969 455 motor (unsure what model vehicle it came from). I put on a new edelbrock 750 carb (using ported vac) and intake. I had an older HEI distributor and just replaced it with a new Summit HEI that has medium weight springs and an adjustable vacuum advance. Used a vac gauge to adjust carb mixture screws.
The car runs strong and fires up right away but it pings only at part throttle. I've set the timing at 8 and it does ping less as I back the timing down from 8.
The HEI intructions said to initially turn the adjustment fitting all the way open counter clockwise. "If it pings at part throttle, adjust the vac advance and if it pings at full throttle, adjust the timing. Adjust clockwise to reduce vacuum as needed".

I've now closed the advance by 5 full turns clockwise and it still pings.

Should I just continue reducing the vac advance until the ping goes away?

Will too little vacuum cause other problems?

Thanks...

SBORule

I have never used a timing light on my car, if you put the timing chain in right you should able to tune by ear, atleast that's what I do.

I would put the vacuum advance back to where it was and just turn the distributor counter clockwise until it doesn't ping @ part throttle.

I'm not a big fan of ebrock carbs, they are OK and east to work on and tune.

If it pings @ WOT go up two sizes rich on jets primary and secondary.

You bought the tuning kit right?

If it shows improvement use the tuning chart that comes with the kit to tune your carb.

cutlassefi

If you've never blown something up then you''re lucky.
Everyone never do it like that, you're asking for trouble. A $40.00 timing light is a lot cheaper than a new set of pistons.

Disconnect the vacuum advance hose, plug it and see how the car reacts. You could have too much total advance. Different HEI's have different amountsof total mechanical. Take your light and see how much you have at the rpm where the trouble is. If it's a reasonable amount then you could have a lean running condition. Step up the jet size or lower the rod size accordingly.

Fwiw, I'm not an Edelbrock carb fan either but they can be made to run fairly well.

1acesmith

I changed the springs on the HEI from the black (medium) to silver (heavy). Adjusted vac advance clockwise two full turns from end. Didn't make any noticeable difference with the pinging at part throttle.

then....
Got the RPM's to 3500 and set the total timing at 36. Initial timing was then 14 on balancer. Shut car off and it wouldn't restart without retarding the timing.

then....
Set initial timing at -2 on balancer and car fires up, idles great, pings less at part throttle, and ping goes away with more throttle. Motor is strong and responsive at -2 initial timing, but slightly pings.

then....
Disconnected vac advance (ported) and took for a very short drive. Car ran strong and responsive and didn't ping at all.

I've read threads where it was suggested to use mix the springs in the HEI, 1- heavy and 1-light. Don't quite understand the reasoning but....?

I have a 2.73 rear end. Could that cause the ping only at part throttle?

The timing gear may have been installed advanced, but I wasn't aware of the issue when I bought it. Timing mark read 0 when we brought #1 piston to TDC.

Adding any vac advance at all makes the motor ping. I'm using 93 octane. The very first time I adjusted the timing after installing motor, I started a 8 BTDC. Pinged like crazy at part throttle and engine temp went up to 225 on highway. Since then, retarding the initial reduces some pinging and motor runs cooler.

Appreciate your help..........

MDchanic

I'm no timing authority, but it sounds like you've found settings where your car runs well, at least.

I would really wonder whether your timing mark is really, REALLY accurate. Have you checked it with a spark-plug mounted stopper bolt or something similar?

- Eric

Rickman48

Sounds to me your balancer might be wrong, or slipped on the ring.
Is it originial to that motor?

1acesmith

Havent checked it that way but im suspecting the same. Very frustrating. Pull motor to replace it?

MDchanic

Naaah. You can get the balancer off by using a puller, usually easier with the radiator out (I've done it, but don't remember if I pulled the rad.).
One step at a time anyway - gotta really check the timing mark alignment closely first.

A spark plug base with a hole tapped in it and a fine thread bolt through it will let you find the exact point fairly quickly (simple to do, instructions are on line).

- Eric

1acesmith

A little sucess....kept wondering why my summit instructions said to start vac adv adjustment fully counter clockwise when everything i look up is the opposite. Called summit tech line and they said instructions were correct, then he said hold on a minute. Came back and said their instructions were backwards. Counter clockwise delays vac advance and clockwise speeds it up. Said they will change their instrucions sheet i adjusted mine counter clockwise and no more part throttle ping and car is very responsive. Going for a drive to see how it runs.

MDchanic

Why pay a proofreader when you've got customers to do it for free ?

- Eric

1acesmith

Another free hat at least?.....