wont idle / help please

New member so I appreciate any help here! I recently purchased a 66 Falcon with a 429 in it. It started up nicely without even touching the throttle. Idle great after a brief warm up. Heard a rattling sound around cyl 1 & 2 area of valve cover. found very loose rocker and neverless a bad cam lobe and lifter. not knowing what was in it I pulled it apart and found a comp cams 305H10 cam. I called and ordered the exact same replacement with a set of lifters. right away it ran shitty. will not even attempt to idle with throttle stop screw letting it go below 1500 - 2000 rpm. double checked everything, even pulling front cover again and checking timing marks. compression is 220 - 240 on all cyl. plug wire routing correct. nothing had been altered on the carb. did find almost white plugs on cyl. 1,5,and 8. vac leak around manifold???? I used exact same part number intake gasket as well but who knows. has offenhauser port o sonic single plane. has been port matched. 750 dbl pumper. only thing diff is cam lifters and gaskets. gonna try to smoke the intake tomorrow I guess. Thanks for any ideas.

THATS why I think iam going roller in my new build

How are you valves adjusted? Maybe too tight?

IT JUST nerve racking breaking in flat cams nowdays LOL

Vacuum leak.

valves were set a 1/2 turn past zero lash. Have already been backed off a 1/4 turn to check that theory. Sure it has to be a vac. leak somehow. Will update on tonites findings.

Assuming "bad" means the lobes are down on it. If so you'll have metal in the engine . I'd tear it down.

ape550 wrote:valves were set a 1/2 turn past zero lash.  Have already been backed off a 1/4 turn to check that theory.    Sure it has to be a vac. leak somehow.      Will update on tonites findings.

Get the vacuum leak fixed bad vac leak will not let it idle worth a flip but make sure you have the cam broke right before you try idling or you going to be changing the cam again.

I'm gonna hook up the smoke machine to the intake tonight. I pray I find a leak!! If it's not I am at a loss. I have double and triple checked everything else. Idled and ran so nice before even with one cylinder down.

Well well well. feel like a dummy. don't know how it happened but the vac. port at the bottom rear of the carb was uncapped. I never touched the carb during the cam change. that's why I didn't inspect it closely. live and learn. Idles just like before now.