I'm helping a friend tune the new 402 in his '86 chevy pickup. 048 heads, edelbrock performer intake, edelbrock 1407 carb, holley red pump, 292 adv duration cam, HEI, R43 plugs, pop-up forged pistons, steel crank, long tube headers and flows. 2500 stall converter in a TH400, 3.42 gears. Unknown cam make or compression ratio. Builder says the CR is 10:1, but I think it may be less.

I'd like some suggestions on a spark advance curve, vac advance settings and carb tuning. Engine runs well but performance isnt as 'crisp' as it should be. Whitish carbon deposits on plugs.

thanks!

chip

You won't be far off on timing if you set it up to give 15 initial and 38 total, with the mechanical advance coming in all by 2800 or so.
The vacuum advance is separate. Most higher compression motors will like * a little* more advance at cruise conditions, say 8-12 degrees. Set everything up with the vacuum plugged, then plug it in and see how much your timing jumps. I don;t think I'd want more than 15 more degrees in vacuum advance. And less, of course, if it pings a bit at cruise conditions. I'd use direct full vacuum.

Originally posted by Chiphead:
Whitish carbon deposits on plugs. sounds lean to me, anyone think this could cause his symptoms?

Thanks for the help so far! We started recurving the dist cuz the truck exhibited rough operation during part-throttle acceleration from cruise. Wanted to make sure timing was right before we fooled with carburation.

The plugs have been in since break-in, and the flaky deposits would indicate rich if they were black, but they were white. Unsure if the plugs are trying to self-clean the deposits left from break-in or what. The ground electrode had a slight buildup of same stuff... could flake it off with fingernail.

Anybody running a 750 edelbrock on a similar setup?

thanks again

chip

Those dry, light colored deposits usually come from additive packages in fuel. Also, canned octane boosters will leave light deposits on the plugs. I'd try using another brand of gasoline and don't add any octane boosters or other "dump in" additives.
Back in the days of leaded high octane fuel, Gulf brand fuel was notorious for leaving white ash deposits all over everything.

Randy