BBC 396 wil not idle with any carb

[nvrenuf]

There’s no reason a choppy cam’d engine wouldn’t idle around 800 or so.

 

[75 Chevy SWB 4x4]

I just built a 414 cu in (.60 over factory 402) BB Chevy in my 72 Monte Carlo. I have a Lunati Voodoo cam, lifters, valve springs, 1.7 roller rockers, 2.19 and 1.88 Ferrea oversized Stainless valves, Edelbrock Performer RPM intake, a 750 Street Demon Holley carb, and Hooker Competition Ceramic big primary long tube headers, and dual 2-1/2" full Pypes performance exhaust system.

First and foremost, directly after breaking in the cam and lifters, I had to ensure I had no vacuum leaks, and my carb floats were set right in the middle of the sight windows. My firing order was correct 1-8-4-3-6-5-7-2. In order for my big block to idle on its own without dying I had to disconnect the vacuum advance and plug off the vacuum manifold port on the carb. Then I set my mechanical advance to 34* BTDC at 3k rpm and I locked the distributor hold down clamp tight so it couldn't move or be bumped. Then I set my idle speed to 800 rpm which makes the base idle timing at 10-12* BTDC. Now it will idle on its own after warmed up and it still has a noticeable lope at idle.

 

[Adriank]

So update on the motor. Found intake gaskets were leaking. Replaced the gasket and engine runs now. But having timing issues now. Not sure how its happened but mark on harmonic balancer is wayyyy off. Engine and starts but dont run the greatest. Moved wires one position over to adjust for the retard of timing and will not run at all. Picture here of it not running but where the timing mark is on #1 with timing light. Thats where it seems to run the best. Would this be wrong balancer? Ive placed it back on top dead center on it sits on the 1 plug of the distributor.

 

[legopnuematic]

You were checking timing with the vacuum advance disconnected and plugged correct?

What type of timing light? Dial back?

Use a piston stop to re qualify the balancer and remark TDC.

I'm not sure on big blocks, but small blocks have two or three locations for timing pointer. For example my 79 is at 12:00, behind the water pump and my 76 is about 2:00 position. Technically you can mix and match, just the marks will be way off. If you qualify it and remark then it's not an issue.

 

[Ricko1966]

So update on the motor. Found intake gaskets were leaking. Replaced the gasket and engine runs now. But having timing issues now. Not sure how its happened but mark on harmonic balancer is wayyyy off. Engine and starts but dont run the greatest. Moved wires one position over to adjust for the retard of timing and will not run at all. Picture here of it not running but where the timing mark is on #1 with timing light. Thats where it seems to run the best. Would this be wrong balancer? Ive placed it back on top dead center on it sits on the 1 plug of the distributor.

It's very possible,and common that the outer ring on the balancer has slipped or the wrong balancer was installed. Buy a piston stop,and follow the directions to verify the TDC mark on the balancer to the timing tab. As for the person running a disconnected vacuum advance.If connected on a ported vacuum port at the carbureator,there would be no vacuum advance at idle or WOT,if the carbureator is adjusted correctly. That is the whole purpose of ported vacuum,no vacuum at idle,no vacuum advance at WOT the vacuum advance woukd primarily be at low throttle cruising speeds, His setup still needs some investigation. And if everything else is correct it should idle whether you are on ported or manifold vacuum,there is one consideration to be made on manifold vacuum though, and that woukd be having the correct vacuum advance cannister to stay fully pulled at idle, advance cans come with different vacuum ratings.

 

[GTX63]

It's very possible,and common that the outer ring on the balancer has slipped or the wrong balancer was installed.

99.9% of the time.

 

[Sad Sack]

It sounds like a radical rowdy pro street engine to me. It would be awesome to take it to a dyno and see if they could tune it.

yup

 

[Adriank]

You were checking timing with the vacuum advance disconnected and plugged correct?

What type of timing light? Dial back?

Use a piston stop to re qualify the balancer and remark TDC.

I'm not sure on big blocks, but small blocks have two or three locations for timing pointer. For example my 79 is at 12:00, behind the water pump and my 76 is about 2:00 position. Technically you can mix and match, just the marks will be way off. If you qualify it and remark then it's not an issue.

I had the vaccum advance disconnected. Port plugged off. Ive got 2 old school timing lights. Old penski and a snap on. Tried them both to see if there was an issue on my first one but they both read the same. They arent dial backs. I set the piston on tdc and was showing on my original marking of the harmonic balancer correct. But while running it is was off.