I dumped my holley in favor of a 2bbl motorcraft. It's 100% better offroad, but I can't seem to get the idle below 1000rpm. The butterflies are completely shut. No appearant vacuum leaks. The idle mixture screws are currently about 3 turns out. If I turn them in anymore, the motor starts surging.

It's a 302, and it runs like a top other than the idle being too high. I have no idea what the motorcraft was off of. Is it possible it's over jetted? Need a rebuild?

You've got a big vacuum leak.

All I can think of is something with the PCV system. My motor runs abosolutely perfect with the holley. I've tried 2 motorcraft carbs with the same problem.

On my engine a tube goes from the base plate of the intake manifold to the filler cap on the valve cover. There is no PCV valve. I don't even touch this when I swap carbs. Could the lack of PCV valve with a motorcraft carb have something to do with it?

Originally posted by Nobody
All I can think of is something with the PCV system. My motor runs abosolutely perfect with the holley. I've tried 2 motorcraft carbs with the same problem.

On my engine a tube goes from the base plate of the intake manifold to the filler cap on the valve cover. There is no PCV valve. I don't even touch this when I swap carbs. Could the lack of PCV valve with a motorcraft carb have something to do with it?

Thats a start, just block of the end of the hose that goes n the breather and see if that fixes the problem. Good luck

Check your timing.....:skull:

Well it does have a PCV valve, it just looked like part of the cap at a glance. The timing is perfect. I can't find any vacuum leaks. The only vacuum line is the vac adv., and the one other port is plugged. As far as vacuum leaks go, it would have to be the gasket or something internal I guess. It just doesnt' seem to be leaking anywhere.

I dunno :confused: :confused: It runs fine with the holley, but I really want to keep the motorcraft on there.

Nobody, Check the play in the throttle shaft. It may be too worn out to keep a good enough seal for controlling the amount of air that bleeds by. I assume you are running the stock style spacer for the PCV fitting. On the side of the Carb there is a number cast inside a circle, 1:08 or 1:12 is most common but there are others like 1:14, 1:23 and bigger yet. this number referes to the Venturi diameter of the Carb. The 1:08 and the 1:12 are suited for the 302. The others were meant for larger engines. they may not have the proper air blead sizes.
Try taking a can of Carb Cleaner and spraying a little at a time around the base of the carb and around the throttle shaft while it is running to track down any possible Vac leak. Be carefull as this stuff does burn very well. the idle speed will climb if the engine sucks in any carb cleaner.

Good luck.

Eric