Holley Carb Issues

[dannystarr]

Well, I took a ride of about 50 miles in one of my cars. Car ran great! 10 days later, got in and fired it up and it won't idle. It WANTS to, but dies in about 10 seconds. It's a 4150 780 Vacuum secondary. If you try to keep it running it does a suck-air kinda thing and goes shss shss shss shss and dies. I got in and revved it out of the idle circuit and kept it running and went down the road. Pulls great, floored it a couple times and it went like hell. Came to a stop sign, down shifted, got into first and pushed in the clutch and it died right before I came to a stop. When you try to start it, it takes ALOT of turning over without giving it any gas and then finally it starts. I looked in the carb and it is squirting gas in well. But that's when I am racking the throttle. But after letting it go back down to idle it dies in a few seconds.
I pulled the carb. Pulled the bowls and metering plates. Installed new 6.5 power valves, cleaned it all up and blew it out. Installed all new gaskets. Set the float bowl height. I didn't do anything else, like pull the needle and seat etc. I reinstalled it and it did the EXACT same thing. I did something I don't normally do. And that is pull a part from a great running car and use it for testing. BUT, I did that to isolate the sitch, and BINGO it ran great. Drove it 70 miles to car a show and back, with no issues. So I KNOW it's the carb.
 Question is.. What do I do next. I don't have the knowledge for complete tear down rebuild. I would rather not send it out for a rebuild and have a 100K car sitting dead for who knows HOW LONG.. Hoping someone here can point me in the right direction. HELP!!! Danny

[uscrichter]

Give Eric with Muscle Car Parts a call at 937-836-1885, he restores classic carbs for most of the NCRS guys, good work fair prices!

[dannystarr]

I don't want to bother him. I am sure he gets 100's of calls all year long from people asking questions. I don't have the time to wait to send it out. It could be weeks or even months. Also, I don't WANT it restored, I like it as-is condition wise. Just want it back the way it was. Hoping for the magic answer. D

[camaronut]

Danny - check your hoses and see if there’s any cracks releasing vacuum…. Maybe vacuum booster?

Good luck..

[wisemanz28]

Danny I was having very similar condition on my 4150 carb. It sounds like a vacuum problem. Mine turned out to be caused by my power brake booster, it had a bad front cup seal.

[RikerZ28]

I had that kind of issue last year on mine. It was the power valve, it was leaking.

 

[dannystarr]

Something I forgot to mention. When I pulled the carb, the back quarter of the gasket was dark colored I assume from fuel. When I put it all back together and tried it that second time, then pulled it off for the swap, almost the whole entire gasket but the front right corner was lightly gas wet. Is that possibly the vacuum issue? Would that cause the gas to be PULLED out? Ironically the second time, I overtightened the carburetor bolts a little just to try to seal what I previously saw. That's when it was even worse. Maybe the bottom plate needs a light surface? Then start with a fresh gasket? Any recommendations on good sealing gaskets? D

[bertfam]

I was going to suggest it may be your needle and seat since lately all the ones I've purchased are total garbage, but you said it worked on a different engine so that eliminates that. Are you using the standard "thin" base gasket or the aftermarket "thick" gasket? I always recommend the "thick" gasket since it helps with better sealing.

Also, what's your fuel pressure? Do you have a regulator? If not, you might need one since you really only need 6PSI at the most for a Holley.

Ed

[LS7]

If another carburetor worked fine on the engine in question, try spraying carburetor cleaner through the air bleeds.

If the carburetor was moved to another car/engine and worked fine, then I would suggest checking the ignition timing, may have backed-off on you.

[dannystarr]

We are getting mixed up. Just to clarify. The carb didn't function properly on car #1 so I took it off. I THEN took a known functioning carb from car #2 and installed it on car #1 and it ran great for 140 miles driving with NO other adjustments. So I KNOW it's the first carb that has the issue. First carb is now sitting on the bench awaiting work.
I will now take it and install it on car #2 that is now without a carb, and try the carb cleaner in the air bleeds. BUT, I will make sure to use a thicker gasket. Anyone have brand/model # of gasket that they like to use. Thanx for all the info so far!! ... D

[Sauron327]

Kurt at Carbs-r-Us in Thomaston CT. Fast turnaround, great rep. Done dozens of carbs for me and friends. Does not do concourse restos for trailer queens. No need to.

[LS7]

Any quality gasket will work fine, but I use these > https://www.holley.com/products/gaskets/carburetor_gaskets/parts/54C

Because this just happened all of a sudden (no tuning changes), I'm leaning toward a restriction in the idle circuit.

Good luck.

[dannystarr]

That gasket would seem to be too thin and not as forgiving. It seems rigidish? I think I would be more comfortable with a slightly thicker cushy gray one. I actually think I have that one in my carb box. I'll check it out, thanx... D

[DuWayne Ladner]

Danny Starr, just went through of your trails with a 4346 780 Holley to the tune of 3 rebuilds, even replaced throttle plate, metering blocks, seats bowls, just about anything that could be replaced, was. Never got it right and my engine guy finally give up on it and I got over this factory like restoration and give in and got a new Quick Fuel 750 and out on my L78. Running smooth as I expected and easy crank! Very happy with it. Hit it pretty hard yesterday and carb responded great.

[bertfam]

Yes, those are the stock thin gaskets which will work just fine if you stack a few on top of each other but I like the singe thick HOLLEY 108-12 gasket.

Ed