New Holley 750 loads up at idle
 

I have 2 freshly rebuilt 454 with new square port heads, vic Jr single plane intake, Lunati roller cams and NEW Holley marine 4160 750 vac. secondary carbs. Both of them were loading up at idle real bad with lots of carb smoke and fuel in the exhaust water. The cams are large with 28 deg of overlap and pull 10 inches of mercury at idle (reading taken from the manifold port under the carb). Both motors pull the 10 in of vac. My port engine pulls 10 inches when checked at the carb. I took out the 6.5 power valve out of that one and put in a 4.5 PV and that seemed to take care of that one. My starboard engine pulls 10 in at the manifold and only 5 inches when checked at the carb vacuum port. I put several different power valves (3.5 and 2.5) with no luck of clearing up the loading idle. You can bring the engine off of idle and it runs great. I even changed the plugs thinking they could be breaking down. I went as far as switching the carbs on the engines and the rich idle was evident on the other engine and the starboard engine cleared up. So, I know its in the carb. I can screw the idle screws in all the way and it just stumbles the engine a little bit, however keeps running. If I cause a vacuum leak at the manifold that helps clear it up a little bit and the idle raises. I called Holley and they had no answer for me other then return the carb. I bought them through a marine speed shop and they will not take them back. I even took the carb apart and put all new blue gaskets in it thinking it had an internal leak somewhere and nothing was changed.

I know its not in the valves or the engine as both motors pull the same amount of vacuum at the manifold and I switched the carbs on the engines and got the same result. Any ideas from you experts. I am thinking about just buying 2 750 double pumpers and get rid of the vacuum secondaries, but these are brand new and cost a bundle!!!!

Have you tried lowering the float levels on the bad carb? tested the needle and seats?

Powervalve opening point has no effect on idle .

is there any fuel dripping from the boosters at idle?

try covering the idle air bleeds with your fingers while idling. If no change, id try blowing out every passage in the idle circuit out with compressed air

If your carb savvy you'll figure it out. I assume power valves are installed the correct side of metering blk. Lol... Also when you set the fuel level did you let it run for a while with float plug out? Almost seems like the fuel is getting to the main circuitry bypassing the pv. Never heard of such a thing however I'd refer to MT's last suggestion. Also MT correct with pv not having any influence at idle however be careful running around with to small of pv. You can lean out. Also if these are actually new and speed shop won't do anything about it send both them back to holley. I would imagine with a receipt they'd take care of no charge.

A lot of money for carbs without rear metering blocks :(

Turning idle mixture screws all the way in and engine still running usually means one of two things
1) Ide speed screw opened far enough that the idle transfer slots totally uncovered.
2) Fuel leaking thru carb somewhere. including as MT mentioned the boosters.

#1 was going to be my guess. Classic still running with fuel screws all the way in.

Thanks for everyones replies. I have done everything everyone mentioned in this thread other then I should have bought double pumpers instead of vacuum secondaries. When this was happening the first thing I did was check the float level. I always take out the plug and let it run to see if fuel comes past the threads. The transfer slots were the next thing I checked and they are a perfect square when the butterflies are shut. I can not see any unmetered fuel dripping down the throat of the carb while running. I took the carb apart and went through every air passage with a straw and carb spray. I think it is leaking air internally somewhere due to a manufactured defect. The place I bought them from and Holley will not stand behind them. I feel like putting an adapter plate on the intake and running my old quadrajunks, they never had any problems!

I rebuilt a carb for a coworkers chevelle. It was a double pumper. I gave it back to him, he put it on the car, and next day tells me it wont idle worth a dam. I figured it was something he did or wasnt doing. So i go to his house the following saturday. I fiddled with that thing for almost half an hour. It just wouldnt run on the idle circuit, it would chug and die.

say there scratching my head. Finally, a light bulb went off. I yanked the carb, and then took the baseplate off. Sure enough, the base gasket i used, the idle discharge ports were blocked by gasket material . Put a new gasket on, making sure all the ports were lined up , put it back on, ran and idled like a dream.

Great thought Mild Thunder, however, I am using a Vic Jr. open plenum manifold with an open carb base gasket.