Help needed with strange SBC drivability problem.

It is the 260hp GM crate motor. My friend had the car before me, decided to put a .510 lift cam in it and other crap, and the car ran so horribly I bought it off him really cheap. I then put it back to "stock".

 

Alignment marks on the gear set. The keyway on the crank points at 1 o'clock roughly, as it should.

 

All stock.

 

Has an HEI distributor in it. I may just buy an MSD streetfire if I don't replace the pickup and coil in my current distributor (the module and capacitor were already changed).

 

It really sound like the timing is retarding to much when you step on the accelerator. 36 deg advance is what you have with full vacuum. but what happens when your foot is in it?
Dizzy curves can really throw you a curve!!! Check it out.

 

I maybe missed it, but has anyone said to "time it out on the road"? without a light?

 

Moloko and C9x, I wondered where you boys went.

I've had similiar problems for a while. Different engine, a Hudson of course - same symptoms. I finally broke down and bought a wide-band A/F meter - and was shocked. I don't know if its the ethanol content in gas these days messing with our favorite former carb tunes, but things are different.

I've had better luck timing by vacuum. Moving it high until I reach max vacuum, then backing off 1" Hg. Idle circuit transition into the main circuit at around 2000 rpms had been a bitch, just like you are describing. While the idle may be fine, the running mix of the idle circuit may be too rich. The Edelbrocks/AFB's have air bleeds for both the idle screw and the running idle mix - check those out. Open up the idle mix hole just a smidge. Another kicker is to set your power valve / step up spring at the same tension as your vacuum advance canister. It might help to install a vacuum gauge and see at what vacuum point this is all happening.

I've had to re-tune and re-curve everything I'm using that burns gas and runs a carb in the last two years. My vacuum points have moved higher, and the air bleeds have gotten bigger than before.

Hud

 

Compression is really 7.9 to 1 They need lots of timing to run , sometimes past 44 btdc without vacuum advance
I have worked on many of them.

 

thinking back to my 86 cutlass.. 350 sbc, ported heads, cam headers high volume water and oil pumps air gap 650 carb, 525 lift cam, i ran 36 total timing and it ran like a raped ape!! 13.2 @104 smoking 28 x 11.5 mickey thompson slicks THREW first gear( th350)..

sounds like its a timing issue weather it be cam or ignition, try throwin a coil off a known good running motor and see what happens, the coil could be gettin weak and not having enough energy at higher rpm

 

I like the idea of throwing "known" parts into it. It lets you rule out things quickly. I always had a spare coil, distributor or carb around that could be swapped in a pinch.

Bob