NOOB Needs some help

[blacks197]

So im new to the 720 realm. What ive got is an '86 720 only mod is a weber carb. Its currently at a mechanics shop and theyre saying that it stumbles real bad and looses fuel pressure under acceleration. The truck idles fine but the mechanic said it keeps trying to switch from 4-8 plug firing causing the stumble. He says all the vac lines are in the correct position and are in good shape( the truck has around 93k on it). Could the computer under the driver seat be the culprit? Any ideas that could get this truck running would be greatly appreciated asmy current mustang on D/R is not going to like this upcoming now. Thanks

[PEZi]

the plugs don't have issues like that firing as far as i know... the intake side fire and then the exhaust side get added in from what i understand... meaning the switching of them from 4 to 8 is flawless and wouldn't cause stumbling

mechanics like to lie... that's where i'll leave it

sounds to me more like vac lines... or something down the fuel line

[seang]

Do carbed 720's come stock with an ECU? Did you swap a carb in place of the TBI?

[blacks197]

Is the plug firing controlled by the pcm under the drivers seat? So far this mechanic has actually been very helpfull,which is shocking to me since ive never trusted my vehicles to other people. He was highly recomended to me by a close friend and so far he hasnt charged me anything for trying to get it to run right. I was thinking about having him block off all the vacuum lines except for the distributor,brakes,pcv. Will unplugging that PCM cause any problems?

It had the stock carb on it when i got it from my cousin. We replaced the gas tank,fuel pump,replaced the cap,wires,cap,rotor,fluids. It wouldnt idle very well so we put on a new weber.It started idling better then we discovered it had a bent valve so we got the head redone and thats where we are at now.

PS this truck also sat unstarted in a garage for 12 years

[noface]

bent valve?

Timing chain problem. Guides worn or broken, jumped a tooth, etc...this would cause the symptoms you describe, and these motors are notorious for timing chains going bad.

[blacks197]

Id ended up that the valve wasnt bent but stuck. I went up and picked up the valve that was replaced,pic below, it looks like a rubber glove got sucked it and melted under the valve. I dont use rubber gloves when working on cars so i can only assume it was a previous mechanics shoddy work.