help

[RatDime]

Hey guys I have a problem with my engine, the only thing I did was replace the water pump and the cyl heads-I went to alum with bigger valves and runners, anyway, the engine free revs great, but under the load it will not go past 3500 rpms then it backfires, spits, and coughs out the exhuast only. What sign is this giving me? I re-ran the valves, timing, checked the plugs and its burning great, fuel pressure does not drop. I bought the heads used-very low miles, and they have duel spring setup instead of my single. piston to valve clearence is good....Im stumped

 

[bowtie81]

Are you using a vacuum advance? what type of distributor? check your vacuum lines and if your using a hei distributor check the 4 pin module. are you running any msd? if you have a 6al box try taking the rpm chip out.

 

[RatDime]

no msd, no vac advance, distib is procomp, but have new accel with super coil going in.

 

[slim69]

u sure u dont have a plug wire crossed

 

[bowtie81]

what do you have your timing set at?

 

[LS6 Tommy]

Sounds like it's too advanced to me.

Tommy

 

[RatDime]

timing is set at 16 int, 36 total. firing order is right

 

[Anonymous]

Assuming all wire connections have been checked, firing order is correct, timing is correct, and the only thing you changed was the heads, I would look closely at the exhaust valve springs for a broken spring, weak spring, or something that is causing the valve to stick open or float under load.

 

[RatDime]

springs are too much, need lighter, figure it out, just too much pressure

 

[Anonymous]

Hope the pressure didn't wear your cam lobes.