Holley problems

[70c10stepside]

Its a 750 vs(year old) and motor is 355. Started with it dieing in gear. After fighting, trying to keep clean fuel filters on it, trash got to the carb. Now the fuel filters are staying clean. But I rebuilt the carb and now issues are coming up still. It is still clean inside, as I have took it off and back on trying to source the issue, being clean inside every time. Including just a minute ago. It just stumbled bad. It'll idle but hops around. One minute worse, one minute better. And it'll idle in gear for a minute, then die from hopping around. When you go down the road it studders getting to speed. Bad. Could it just be bad gas? Or worse? I can tighten the mixture screw all the way in and it will cut off. But I realized a minute ago the speed screw does not really seem to be affecting it. At all. Could this be something to the issue? The accelerator pump screw is set to 15 thousands at wot. All float levels are where they are supposed to be. Its got plenty off fuel pressure. Ideas? Simply bad gas?

[70c10stepside]

Also neeed to add the rockers and all are moving like they should, new spark plugs didn't really help and it has new cap and rotor. But still looked over them and they appeared fine. The mechanical advance is also still fine. Popping back like it should. I think I just got a batch of really bad gas. But would like to hear if something else could be causing this while doing the rebuild on carb. If someone has had something similar maybe. A vacuum leak wouldnt be this annoying if it were that, would it? The gaskets appear fine though.

[sean1969c10]

It kind of sounds like a vacuum leak. The idle screw not having much effect on engine idle speed sounds like air is being introduced from somewhere else. Spray carb cleaner around the base of the carb and see if the idle picks up, if the truck will cooperate and run long enough. Have you ever noticed if the well behind the power valve is wet when you take the metering block off? It's not uncommon for the metering block mounting surface to not be "flat", and this could cause an internal vacuum leak. Just a couple ideas to look at, good luck!

[MARKDTN]

Did you change the power valve? If it backfires, it can take out a power valve and run bad.

[70c10stepside]

Yes, power valve was changed and checked a few times. Regasket as well. I will check for vacuum leaks

[JayB331]

+1 on the vacuum leak. Got a buddy who's '62 nova has been acting up for a few weeks, idling rough and backfiring. We found the leak between the master cylinder and the booster

[70c10stepside]

^ thats an interesting one.

Finally got it. Was do to one of the carb studs. When I thought it was snugging up, it was stripping itself backing out the stud. Kinda rigged it by retapping it and putting a 3/8 bolt. But will work for now I hope

[GASoline71]

Unless the carb was built before 1993, it has backfire protection already built into the carb. If it's an earlier model Holley then a backfire could take out the power valve. So if it's a later model Holley, I doubt the PV is blown.

What manifold have you bolted this thing on. The stock cast iron manifold? What model Holley 750? The 750's are all sqaure bore carbs and the stock intake is a spread bore.

It sounds like a wicked vacuum leak to me.

Gary

[70c10stepside]

Edelbrock torkii 2. And 4160 street/strip. Now thats fixed. Once I got the timing set back right and floats back its back to normal. Woohoo!

[70c10stepside]

Ok, another slight issue.. Has me confused. Before this crap came up I could set my idle at 700-750 and it'd count them off at 450-600 in gear. Now, when the motor is cold, it'll still do this. But once the motor gets to operating temp you can forget it. Have to idle it at 1100-1200 to get it to idle 700-800 in gear. Any lower it'll die as soon as you put it in gear. Like literally, just cutout. Done. What in the world could this be? At first I though the fuel lines were getting to warm, so I rerouted them. Did not help at all. Has no choke, just the stock mechanical linkage on the side. Float levels are were they should be. So? I am confused..

[GASoline71]

Could be the big open plane intake. Not the most street friendly intake. Still sounds like a vacuum leak to me. What camshaft is in it? And where is your timing set at?

Gary

[70c10stepside]

It used to be fine. I think I had the mixture screws to lean. I think it's fine now.. Will no Friday. Cam is 508 lift with 313 duration, and timing is like 18 or so initial with 32 total.