[Andy327]

It just won't work right. At 4 deg. btdc, it diesel's when it's turned off. (chug chug...........chug...rattle) Plug in the vacuum advance and it goes well past 12 deg. There was alot of spark knock until I changed to premium fuel and octane boost. It's sluggish at low revs and it falls on it's face when I tramp it. Is it the HEI, the vacuum adv., centrifical, the 750 Q Jet, or compression.

[Chevrolet4x4s]

take it to 6 to 10 btdc and try that
Shane

[barnym17]

advance it to 10 degrees to start with with the vacuum advance unplugged and the idle as slow as it will go without dying(to prevent centrifigal advance from skewing the readings)should be under 1000 rpm. Then reconnect the vac advance and reset your idle speed. Run on is usually caused by to large a throttle opening at idle not ignition timing (there is no spark with the key off so timing has no effect).However what happens is when timing is advanced idle speed rises helping add to the problem you must reset your idle speed when you are done.Then tune from there most sbc with stock heads like 36 to 38 total without vac advance all in by 3000 as a general rule(results may vary)

[F-BIRD'88]

If you have an older 327 that has small chambered hi perf heads and a domed piston the compression ratio of that engine is too high for regular 87 octane gas.
You can ID what heads you have by removing the vavle cover and reading the casting number. If you have any of the various versions of the old 327 camel back head (461-462-292-291-041-186-etc etc) you should be running premimum fuel. Do a compression test. If you have more than 160psi you need premimum fuel.
You need to be running premimum fuel. Check and verify the total timing (32 to 36deg BTDC) make sure you have the correct spark plugs. Non projected tip type plugs of a slightly cooler than stock heat range will help. Look for the spark plug listing for a hi perf 327 from a Corvette that uses the same heads as yours. The spark plug heat range will be a few levels cooler than the plug from a low perf low cr 2bbl 327.
Gm cars used to come with a anti run on solenoid on the carb. The solenoid was activated when the key was turned on to set the idle speed. When the key was shut off the solenoid closed, closing off the carbs throttle blades completely.
This "choked the motor's air supply off completely so it could not "diesel" when you shut it off. The idle speeed is adjusted by the plunger extension adjustment on the anti run on solenoid, not the carb idle adjustment screw. The carb idle adjustment is set to close the throttle off when the solenoid is not activated. As an engine get older and gets a build up of carbon in the cylinders and a little oil now sneaks past the rings into the combustion chambers, the octane requirement of that engine goes up.

One way around haveing to run high octane gas on a high compression ratio motor is to install a water injection system.
www.snowperformance.net

[Andy327]

I changed it to 8 deg. and it took the flat spot out. It'll light it's tires now. F-Bird'88 asked about the heads. When I bought the motor, there was a set of 882's sitting on top, but people thought they were too big. So I ended up getting a H.O. 305 out of an 88 Camero. The center bolt heads had 194-160 valves and I believe 64cc chambers. It also had an older GM performance alum. intake. So there's the top end that went on.
I did notice something when I changed the timing. The carb is wet on both sides, so I think that might have something to do with the dieselling. The low speed jets are 1 1/2 turns out and the idle adjust. isn't even making contact.
One more thing. If you don't have a fan shroud, watch your knuckles!

[leprosy]

[QUOTE=Andy327]So I ended up getting a H.O. 305 out of an 88 Camero. The center bolt heads had 194-160 valves and I believe 64cc chambers. QUOTE]

I ran 305 heads (early 70's) on a 350 below and had similar issues -- my issue was the CR, bumped the gas to 91octane (as suggested above) and all was well. Had about 12deg of timing into it.

I found 89octane was too low, and 94octane wasn't required. This is all assuming you don't have any methanol content in your gas.

[jimfulco]

Originally Posted by barnym17

Run on is usually caused by to large a throttle opening at idle not ignition timing (there is no spark with the key off so timing has no effect).However what happens is when timing is advanced idle speed rises helping add to the problem you must reset your idle speed when you are done.

What he said. Try backing off the idle speed a little bit.