duswill

We just rebuilt our short block due to a destroyed piston and scarred cylinder. The only change to the engine was boring the block and putting in a 14.2 to 1 set of pistons from a 12.9 to 1 set. Compression is good in all cylinders. Everything else is the same. At idle it sounds like it is hitting on about 5 or 6 of the 8 cylinders. When you bring the revs up it sounds fine. We have checked the plug wires all test good, replaced the dist cap and rotor, 2 different sets of plugs, double checked our valve settings and we don't know where to go next. The ignition is a Msd Digital 6 with an HVC coil and a locked out pro billet dist. Any suggestions on where to look next would be appreciated.

fla1976

Could be a vacuum leak. You could try spraying some WD40 around the intake and listen for a change in the idle. If it changes temporarily , you have found the leak. It's a little messy but safer than starting fluid.

duswill

Already tried that, no leaks. Thanks

hammertime

Are all the plug firing ? Have you changed plugs out for another set ? Timing isnt way off is it ?

johnracer

Maybe you have a 4/7 swap cam but have it wired with standard firing order....

olds48

Like Hammertime said,I'd put a timing light on all 8 wires and see if they are firing.Any chance of a broken valve spring or that the timing set is off a tooth?I got a chain off one tooth one time in a hurry and it sounded like that