SBC timing question (1 Viewer)

[TCinVA]

So I actually drove my cruiser after a long install process. I have a 350/290 HP crate engine. I put an HEI distributor and a quadrajet. I just guessed at the timing and drove it to a mechanic friend nearby to help it idle better and set the timing. There were so many vacuum leaks on the carb we had a hard time. He set it at 12 degrees(he said 10-20 was good) and said I had it close to 45! When I got it home I fixed all the vacuum leaks and got it idling well and took it for another ride and it was noticeably less powerful. Before, it jumped when I goosed it, now it's a dog. Should I just rotate the distributor to advance it by ear? As long as it isn't pinging am I hurting anything? Which way is advance? Sorry for the long winded post, I wanted to put all the parameters out there. Thanks!

 

[fieldsken1]

ok heres mine i started with a holly truck advenger 670 and heres what i did to it. i removed the 28 primary squirter and replaced with a 25 and i changed the accel pump cam and spring adj float level and i left the main jets alone. 5% at idle 4.5% at cruise. i also disconnected the vacuum advance recurved distributor for machinical advance. no more vacuum advance its 20 degress initial timing 38 degress total. and i used the same crate motor as yours hope this helps

 

[pb4ugo]

Turn the dizzy counter clockwise to advance.

 

[pb4ugo]

You don't want it to ping under load, go maybe 25-30mph in a high gear & give it gas to see if it pings or lug up a hill.

 

[Cdaniel]

Be sure every vac leak is gone.

Get a timing light. Or a vacuum gauge.
With a light, the static timing on a 70's era Q-jet fueled 350 is 8-12 deg BTDC. at about 800 rpm idle

With a vac gauge, adjust advance until you get the highest vac reading possible.

Total advance and curve is whatever the motor is built for. As a baseline stock is about 35 (I think). More than 40 is pushing it. How and when it gets there is the curve that effects if it pings or not.

Timing advances when you twist the dist CCW

Idle mixture should be readjusted if you've got major timing/idle speed changes. This could explain the sluggishness. Make sure the carb is actually idling in the idle circuit


edit: looks like I was late in some response

 

[Cdaniel]

i put in another accelator pump spring and i unhooked the vacuum advance and installed a mechanical advance and the timing is set at 38 degress and runs great and i have the same motor as you

"accelator pump spring"? What effect did this have on your timing?

 

[fieldsken1]

"accelator pump spring"? What effect did this have on your timing?

it helps the carb to work better and they all work together
everything has to work right to work together

basicly everything needs to be improved

 

[TCinVA]

Thanks forthe replies, i can get on it tomorrow.

 

[BrianSanDiego]

Good info here....

HEI Tuning Secrets

I got the Crane timing kit and followed these instructions and my SBC runs like a champ. Hope it helps,
B.

 

[TCinVA]

Thanks, man.

 

[ingomar]

Do you have a dial-back timing light? If you do or have access to one, disconnect the vacuum advance and slowly rev the motor up until the timing stops advancing. This may take 3500+ rpm. Then, use the dial on the light to put the timing at the "zero" mark on the engine timing tab. Read the timing light dial; this is your total timing.
Most Gen 1 SBC's like between 36-38 degrees. After you lock the dist. down, check it at an idle. It'll probably be between 8-12 degrees, depending on the amount of mechanical advance in your dist. From now on, once you know this, just set it at idle if you need to. Also, I think it's best to hook the vacuum advance up to the "ported" vacuum stub on the q-jet. This is the one that has no vacuum at curb idle, but as soon as you crack the throttle open, vacuum is present.