I've got a stumble at lower rpms 1800-2800 on my 86. Sometimes its worse than others, usually worse at part throttle, under load like cruising up a hill. When I floor it, it flies through the "stumble band" and pulls like all hell. Shift to second and it breaks the tires loose again. Whats might be causing this stumble? Here is a run down of whats on the car:

-.060 over gen 1 350 freshly rebuilt
-summit 1103 cam
-305 #416 heads untouched except for stiffer springs
-performer intake
-gm hei ignition (came off a 79 truck... guy said it had a new cap and rotor, looks new)
-rapid fire plugs gapped at .035
-holley 1460 600 cfm vs carb ( this hasn't been touched other than a rebuild, this is one of my prime suspects, i havent changed secondary spring, or jets)
-headman long tubes with true dual exhaust 2.5"
-th350 tranny with stock converter
-3.23 open differential rear

Thanks for any help you might be able to give me

 

How are the plug wires? Miss under heavy load sounds like ignition.

 

plug wires are a little burned, due to the headers and a few screw-ups. They are 8mm 90* boot wires. I planned to replace them here, shortly...

Why wouldn't I notice the miss or stumble in the higher rpm band? Is the motor just turning fast enough I cant pick it out?

Thanks

 

Thats my guess. The high rpms smooths it all out. The burnt plugwires, I'd say, are almost definitely causing your problems. You can buy some heat resistant boot sleeves for those and they'll last quite some time. I have equal-length shorty headers aka plugwire eaters) on my Mustang and am running 45 degree MSD 8.5 wires, with boot sleeves...theyre been on for probably a year now with no problems at all.

BTW, what kinda 8mm wires?

 

The wires on there now i think are just some generic 8mm's. They were on the truck that I pulled the motor and tranny from. So i used them. I'll probably go with some msd's or accells for new ones.

 

I recommend the MSD's... Taylors are also good for a much cheaper price. I don't trust Accels...their 300+ race wires or whatever may be good, but their generic wires are crap.