Hello first post here, this is a cross post from Cbodiesonly I was told to post this here as there is more small block guys in Abodies.
Been pretty stumped the past six weeks so I'm coming here as I'm all out of ideas.
I have a 1967 Plymouth Fury III I'm stalled on because of the motor. I rebuilt the engine, first time doing this, just a home drill hone and re ring. It's a forged crank motor with 920 heads I had decked 20 thousandths and running a 38 thou felpro head gasket I believe compresses to 38 thou and ported the heads by hand. Running a comp 20-233-3 cam which I did manage to break in properly at least, all the lobes looked good when I pulled the intake. Got a JEGs airgap style intake (I mention this because it may be the problem). Im also running a 1980 dodge ram pickup spec electronic distributor new from rock auto triggering a DUI 4 pin HEI module wich I did bench test for spark.
My issue is the engine refuses to idle down even with the throttle set screw backed out on both my known working Edelbrock and factory reman Holley brawler 650. Same issue both carbs and is certainly running rich. Black but dry plugs. I swapped intake gaskets already switched to the felpro 1213 I think is the number. Ive done the intake six times now, 1213s, steel shims, 60 thou felpros, 30 thou felpros you name it. Dry without sealant, with sealant, gooped to hell with sealant. Last time I pulled the airgap I for the life of me could not find anywhere the peramtex failed, and the motor didn't even run right for a few seconds at least right back to where it was. Cannot find a leak anywhere with ether externally which leaves the valley pan. I tried plugging the pcv and holding the breather port right to see if it affected the idling with no luck. No noticable suction and no definitive oil in the plugs. If i cover the primaries the car dies pretty quick, like within a second or two.
I almost tossed the intake and found a period 70s Holly street dominator intake that fit perfectly, bolts holes lined up dead center. It didn't rock around in the V of the heads even a hair, it fell in rock solid. Used metal shim gaskets and a smear of gray permatex and all the bolts went in finger loose didn't interfere with the intake at all, and even then it ran exactaly the same. Nothing I have done has changed even the level of the leak so im starting to think its not the intake.
I have done all the basic stuff, checked for vacumm leaks, plugged vac lines, no power brakes, no vac advance, all the plugs are in the intake, no blind holes are sucking in, tried swapping the wires on the distributor, no binding of the throttle likage disconected. This motor if i turn the timing up to 14-16* will spin above 3000rpm with the throttle blades fully closed, idle mixture screws do nothing it just pulls fuel. Both the carbs I have do this and edelbrock is running on my pontiac I know its good. Cam was installed dot to dot I have photographs no advance notches just a basic double roller.
Engine is making strong compression holds 150psi after a ten or so seconds of cranking. I made the mistake of not doing a bleed down test which is my next step because I have a theory.
Im wondering if the stock 67 rocker arms and pushrods are causing the valves to stay open and while it builds compression at cranking when under full oil pressure could the valves be hanging and need to be shimmed or shorter pushrods installed? the lift of the cam is around .478 and .480 iirc. Would that cause these symptoms because im not sure about pulling the intake for the seventh time, because when i took it off last time i threw so much goop in there theres no way it wasn't sealed at least intitally for a few seconds and why would thus leak be identical in its intensity no matter how many intakes and gaskets I use?
Any help troubleshooting this would be appreciated. I'm very stuck and this car is about to be back burnered unfortunatly.
