As for changing cam, that would also mean changing lifters. Most folks pull the motor and invert it to do this. Not something done for fun and kicks.

+1 on a compression test. If you have uniform cranking pressure in all cylinders, you don't have valve or ring problems. If you still have 2-3" of vacuum fluctuation at idle, I'm guessing it's your cam and the engine is fine. From what I can tell, Y-Blocks like a narrower LSA than scrubs... while the idle may be a little rough, the peak torque will develop sooner, along with a satisfying shove in the back!

Main jets shouldn't effect idle much... have you set the idle mixture screws? It's simple with a single 4V, I don't know about a dual. If you can't get it to idle below 700rpm (with no vacuum leaks), you have a wilder cam than I do!

It idles a little lumpy but I can't get it to idle below 700 RPM. I'm sure it because of the carbs. I'm planning on rejetting them soon. Guess I gotta put a cam in it too

58 Ford Custom 300 - San Pedro, CA (So-Cal)

easyissy: the fact that you have no info on the Cam & haven't indicated what the engine idles like.. is it somewhat lumpy or is it smooth? What speed will it idle fairly well at?. This makes it difficult for anyone to give a definitive answer to your problem. The other thing is that Two 500 cfm carbs on anything but a fairly modified engine is likely way overkill..

Paul

Ya, think I'm going to try that first.

Thanks for all the help.

58 Ford Custom 300 - San Pedro, CA (So-Cal)

I'd recommend a compression test if the erratic vacuum bugs you. Much less intrusive than pulling heads.

I adjusted the valve lash before taking the vacuum reading. It jumps around by about 2-3" of vacuum.

58 Ford Custom 300 - San Pedro, CA (So-Cal)

"Came too close to dying to stop living now!"

I get about 14" at idle (~500 rpm), and less with the FOM in Drive. Mummert Y265S cam, .040 over 292, "B" manifold/holley 1848-1 (465CFM), '113 heads. Runs great, but has enough valve overlap that the vacuum is a little jumpy at idle, and increasing valve lash won't take that away. No vacuum leaks, runs very strong, but doesn't have much vacuum assist for the brakes!

I've learned to live with it, and just enjoy the car!

How's your valve clearance? If they're too tight they can cause low/erratic vacuum readings by not closing completely.