I am having a problem with a rough idle on a 1966 Mustang with a 289, hydraulic lifters and a 4-barrel carburetor. First the background. I replaced the engine about forty thousand miles ago with a rebuilt short block. I have never been able to get the engine to idle smooth since I installed it. It doesn’t consistently idle rough like it would with a high performance cam (the cam is only slightly hotter than stock). I thought at one time it might be a warped carburetor casting periodically dripping raw gas into the manifold. That is probably the best way to describe it. I am a pretty good back yard mechanic but when unsuccessful I have taken it to three different mechanics for adjustment/analysis. I have replaced the carburetor, distributor, plugs, wires, points, condenser, distributor cap, fuel filter and still the rough idle persists. I have adjusted everything twice and then had professional mechanics adjust them again. About a month ago a valve spring broke so I pulled the heads and had a valve job done. Still the problem persists. I first adjusted the valves cold (zero lash and then ¾ turn). With this adjustment the intake valve was not closing on one cylinder. A compression test indicated about 140 lbs for all cylinders except one cylinder that was zero. By backing off the adjustment to about ¼ turn I could get compression. I readjusted the valves hot and still couldn’t use more than ¼ turn on the one problem cylinder. Now for the question, I think I am having a problem with an intake valve hanging open, is there any way I can test to verify this or should I just replace them all?



Charlie Stephens