I will start by telling eveyone my combo. I have an 87 s10 with a 350. The engine has a comp cam XE274 cam, 1.94 ported heads, 1.5 roller rockers, Hurricane single plane intake, edelbrock 750 carb, Super Comp headers, Mallory magnetic breakerless distributor and MSD6A ignition. The trans is a TH350 with 2500 stall and rear has 3.42 posi.

The best my engine has run was after it left the mechanics with fresh plugs and the timing set. Ran high 12s. The timing started jumping so we pulled the distributor and put it back with new springs and bushings. I dont have a timing light or the dollars to send it to the mechanic again so we set it by ear. The truck now runs high 13s. The truck blows some serious black smoke when racing now and doesnt seem to rev freely to 6000, almost surging.

Heres the questions

1) Could the timing be off that much to kill my 1/4?
2) Could my 750 carb be fouling my plugs?
3)What plugs and gapping would you recommend?
4) Would putting on my spare Holley 600 solve the richness problem and still give plenty of gas/power?

Any other advice would be greatly appreciate