Author Topic: Holley Carb Issues (Read 2854 times)

dannystarr · « **on:** June 10, 2023, 03:52:15 PM »

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 · « **Reply #1 on:** June 10, 2023, 04:36:23 PM »

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 · « **Reply #2 on:** June 10, 2023, 05:00:36 PM »

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 · « **Reply #3 on:** June 10, 2023, 05:48:15 PM »

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

Good luck..

wisemanz28 · « **Reply #4 on:** June 10, 2023, 08:11:41 PM »

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 · « **Reply #5 on:** June 10, 2023, 08:22:12 PM »

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

dannystarr · « **Reply #6 on:** June 10, 2023, 10:39:46 PM »

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 · « **Reply #7 on:** June 10, 2023, 11:25:45 PM »

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 · « **Reply #8 on:** June 11, 2023, 12:38:42 AM »

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 · « **Reply #9 on:** June 11, 2023, 02:06:19 AM »

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 · « **Reply #10 on:** June 11, 2023, 01:52:57 PM »

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 · « **Reply #11 on:** June 11, 2023, 02:00:14 PM »

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 · « **Reply #12 on:** June 11, 2023, 05:00:55 PM »

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 · « **Reply #13 on:** June 11, 2023, 05:25:00 PM »

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 · « **Reply #14 on:** June 11, 2023, 05:35:44 PM »

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

dannystarr · « **Reply #15 on:** June 11, 2023, 10:33:08 PM »

Thanx...That bad-boy looks pretty thick. Probably seal up well. Problem is, I already have a 1/4" Phenolic spacer to help prevent fuel in bowls from boiling. I am almost flush with thread height. I think I need one between the 2 that is not too solid. I don't want to install longer studs if I can help it. I better do some more research. Keep the ideas coming. D

DuWayne Ladner · « **Reply #16 on:** June 12, 2023, 01:08:13 AM »

Yep, gaskets now a days or simply not good quality gaskets, as my builder showed me metering block gaskets that were way out of place on most of the passages. Again I ‘m gonna jump this high horse, of most of the old faithful venders in our hobby is not getting good quality stuff from the far east! Believe me, as I know from a repair business that I was in for 30 years, last 10 to 15 years, raw products going far east and pure junk returning in the form of replacements parts. Dealt with a lot of brass and stainless steel, soldering the 2 together. I’ll stop.

bertfam · « **Reply #17 on:** June 12, 2023, 01:57:17 PM »

You really won't need the phenolic spacer if you go with the thick Holley 108-12 gasket.

Ed

jdv69z · « **Reply #18 on:** June 12, 2023, 03:04:22 PM »

What do the plugs look like? Too much fuel at idle will cause all kind of headaches. Plugs will be carbon black, will foul prematurely. I was thinking bad power valves, but you replaced them. Power valve is basically a switch turning on and off additional fuel under power. If the power valve diaphragm is ruptured, that additional fuel will be added all the time which would cause excessive fuel at idle. The diaphragms can be damaged by backfiring. High Vacuum at idle holds the power valve/switch closed. Just some ideas.

dannystarr · « **Reply #19 on:** June 13, 2023, 02:26:29 PM »

Ed,
I didn't realize that thank you. I may pull that phenolic spacer and try the Holley one. If I can get some heat insulation AND better sealing, I am in!

I pulled a couple plugs, and they were dry as a bone and light brownish. No sign of any fouling. My friend said set the carb on the intake with NO gasket and see if it rocks. I will check the base for flatness. I drilled/installed the backfire valve/ball to help things out if it does backfire. But no backfire issues even while trying to keep it running. It sure seemed like it wanted to backfire bad, but never did. That's why I feel it is a fuel idle circuit issue. And not an ignition issue. I am burned out on it for now. I'll get to it in the coming days. Meanwhile car #1 is still running good with car #2 carb. So I am going to just leave it be.

QUESTION... Should I run the 2 slot or 4 slot power valves?... Does it make a difference?... Also, do we know who make the best quality Valve? D

1971ls6 · « **Reply #20 on:** June 18, 2023, 01:56:47 AM »

4 window are supported to be quicker, for the price difference, it’s worth it.

Remove your needle and seats, take a good look and clean it with brake cleaner

lynnbilodeau · « **Reply #21 on:** June 20, 2023, 01:35:49 AM »

Sounds like it is loading up with fuel. Here is the clue: "When you try to start it, it takes ALOT of turning over without giving it any gas and then finally it starts."
Classic sign of a carb letting in too much fuel.

Because you already changed the PVs, probably needle and seat. May not even need replaced. May just have a bit of junk in it not allowing it to shut off fuel.

NAPA68 · « **Reply #22 on:** June 24, 2023, 10:11:03 PM »

Danny,

I'm a bit late to the party for this conversation. Am I safe to assume your carb is full rich at idle? If so, try this. With the carb off of the engine, place it on a carb stand (or some equal length 5/16 bolts that are secured to the base plate to suspend the carb). Fill the float bowls. Does the carb leak down while the carb is sitting there? That would only get exaggerated by engine vacuum at idle.

As you get it off of the idle circut......it runs fine. Of course, engine RPM can cover up some some fuel and ignition problems. If I were a betting man, I'd say the issue may exist with one of the metering blocks / gaskets / and or main body fit. It sounds like fuel is getting in where it does not belong when it's supposed to be working strictly on the idle circut.

That all having been said, I too would suggest reaching out to Eric @ Vintage Musclecar Parts. Eric does ground zero rebuilds above and beyond full restorations. So often, I found out how warped the main bodies are, to say nothing for the metering blocks. Eric recently helped me through an problem child 4150 that was on an LT-1 Corvette. It was an issue as I described above.

I can appreciate yoiu not wanting the bother anyone, nor laying the car up for a period of time. In my own humble suggestion, put a pro on it. You'll save time and aggrevation that you would not otherwise be able to put a price on.

Tim

sixt9x33rs · « **Reply #23 on:** June 27, 2023, 02:21:27 AM »

Danny I suppose you have no gas coming out of the vents or flooding anywhere?
I would check the needle and seat and confirm no trash has found it’s way on the seat.

dannystarr · « **Reply #24 on:** June 30, 2023, 12:54:50 AM »

Finally got some time. Pulled the carb. Pulled it apart part way. Cleaned it all up and sprayed it down with carb cleaner and blew it out. ALL the holes on both metering plates BOTH sides. Installed new blue gaskets. Set new gaskets with light greasing on intake. Starting hooking things up. Went to put the throttle rod C-Clip on with a screwdriver push and it went flying into the cowl vent. Found a small thin baby magnet and fished it out. Good Times!! Fired it up and had a couple bowl leaks. Tightened them up and a few seconds later... cha cha . cha... cha chug chug chug chug chug and dies. EXACTLY what the hell it did before. It ran approximately 35 to 40 seconds. Gave it a little gas and tried to start it, and it turned over like wildfire, all-the-time trying to start but didn't/wouldn't. I will pull it again and check the needle and seat, as I forgot to do that. After that I am sending it out? NOTE: The throttle rod dripped on the left side, but only while the car wasn't running. Never leaked a drop there before when it used to run great... D

dannystarr · « **Reply #25 on:** June 30, 2023, 07:46:09 PM »

I think I figured it out. I was cleaning the needle and seat and noticed 2 or 3 baby threads. I put a new one in and set it. Wouldn't start. I went back to check it and it was sticking up 1/4" past where I set it. I can move the needle and seat up and down in the bowl by hand. Female threads are stripped out! I need a bowl. I contacted Summit, Jeg's, classic car parts places no go. Even Holley won't have any until 8/04/23. They should have 100 available, ridiculous!!

Anybody have a front primary bowl for a List 4053 / 4150 Series 780cfm Vacuum Secondary? HELP!!! ... Danny

dannystarr · « **Reply #26 on:** June 30, 2023, 08:40:03 PM »

I think I found one... D

dannystarr · « **Reply #27 on:** June 30, 2023, 09:23:27 PM »

NOPE, still need one.. 134-103 D

uscrichter · « **Reply #28 on:** July 06, 2023, 08:26:53 PM »

Try Phillip at Custom Carburetors

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Author Topic: Holley Carb Issues (Read 2854 times)