More Holley help needed-this will be the last one.

[n737nc]

OK, I am getting really tired of messing with this thing!
Had it rebuilt by a carb shop that specializes in Holleys. So I figure that they know what they are doing.
Put it on last night, and it would run but no idle. Couple of people here gave me some advice, but still did the same thing no matter what.

This morning, I took it back to the carb shop and he told me it blew a power valve. He installed a power valve block off plate to get me going for now(I need to get it running in order to see how much vacume I am pulling so that I can get the correct power valve).

Well, I tried it again this evening with the block off, and still does the EXACT same thing.

It will run fine as long as you give it gas. But if you let off it will die. If you try and hold it at one throttle position, the RPM's jump all around..

[n737nc]

Sorry, it's a 700 DP

Any help would be apreciated!


Thanks,
Nick

[68C15]

vac leak?
float level?
I tell you what, box it up & send it to me. I will go through it for free (except whatever parts needed). just need to know engine-truck specs.

[jhow66]

You said it blew a power valve. Did it backfire thru the carb at any time?

[n737nc]

I didn't hear it make any noises that sound like a backfire. But, there was a little(very little) black soot around the choke area.

I took it back to the shop that built it and he told me that the power valve was probably blow. He then replaced it with the block off plate and I took it home. It did the same thing that it did before.

I took it off and ran it back up to the shop this morning. I asked them to please go through it again.

It sounds like a vacume leak somewhere. But, I can bolt on the Edelbrock 600 that I have, and it runs perfect(aside from being way to lean). Bolt on the Holley, and problems start up.

I am clueless.

Nick

[jhow66]

If they rebuilt your carb a new power valve would have been installed. If it did not backfire hard thru carb the power valve would still be good. (was it a used carb?-was it clean when you got it back?-was it working before you had it "overhauled"?) There are a few things that will cause your problem--floats too high--blown power valve-wrong gasket under power valve--wrong gaskets on metering blocks and rear metering plate--choke staying closed--mixture screws out too far-(if stock engine 1 turn out will get you in ball park.)--idle speed screw set to low. A vacumn leak will not make it run rich (would be lean because of extra air) but will affect idle speed (would be higher). Forgot to add one thing--floats to low will cause no idle and jumping RPM.

[n737nc]

Yes it was a used carb. I don't know the history on it. That is why I took it to a professional to have them check t out, and rebuild it.
It was very clean when I got it back. I have no idea if it was running or not before I got it. I got it with a bunch of other parts. The guy that rebuilt it said that it was in really good shape. One of the best used ones that he had seen.

I checked the float level, and the fuel sits just below the sight hole. Maybe 1/16 below.

It runs great as long as your reving it. But, like I said, it will not idle or keep a constant RPM.

[jhow66]

Do mixture screws have any effect on idle? What kind of engine?

[n737nc]

It's a 350 bored 40 over. XE282 cam(pretty lopey). World product heads. Weiand Team G intake.
The mixture screws(assuming that your refering to the 2 screws on the front metering block), they have little affect on the way it runs. The lowest RPM I can go before it dies is around 1K, and it will not stay there more than a second or two. So, I can not answer how they affect the idle.

[jhow66]

Went back and read your post about Edlebrock and Team-G manifold. Is manifold a square bore (4 holes or open square ) or a Q-Jet shape?

[n737nc]

Open square

[jhow66]

can't find a XE282 --can find a 262 or 284. (checking to see what vacumn it should pull) Carb you got should fit manifold ok. check cam # again. Sorry I took so long-had to eat supper.

[n737nc]

Sorry, just went and looked it up again. XE268

[jhow66]

That cam should pull 15 to 18" of vac. A 6.5 or7.5 power valve should work ok. Have you tried a vacumn gauge yet? Have you got all vacumn ports on carb closed? Gaskek under carb should be open square like manifold. With that cam you should be able to get it to idle in gear with no problem. Does it smell rich when you are trying to idle? Sorry got to go -be back later.

[n737nc]

Have not tried a vacume gauge yet.
All ports are sealed off.
Gasket under carb is the same as intake.

Can't say that I can really smell a rich smell. But, if it is running it is past the idle rpm's.

[WRMZ71]

The mixture screws will effect your idle speed but just not usually a lot. the old school way of doing that is with a warm engine so the choke is off. Then back out each screw about 1/4 of a turn at a time both screws equally. You will notice the engine RPM rising a little bit. Usually this way you will screw out until there is no more difference in the engine. Vaccuum gauge is a better way of doing it by far though. You want to adjust them out till you get the most vacuum possible is how i've been told to do it.

[68C15]

it is possible there is a piece of old gasket material stuck in the idle feed orifice in metering block. blow all passages with blow gun
also possible that it had this problem before & that is why it went for sale with a bunch of other parts. Holleys are known for having porosity in metering blocks. what is the suffix? (4777-2, -3)
how far are the secondaries open? is baseplate-main body gasket in correctly? is the acc. pump shooter check valve in place?
try adding some propane down primaries to see if it is lean. if it seems better then it is lean & viceversa.

[n737nc]

I took it back to the shop that built it. And I had him tear it down again just to make sure I didn't get any trash or anything in it. He found absoluty nothing wrong. The #'s on it are 4778-4.
My biggest problem is that I am doing this by myself. It will not idle at all, so getting in the engine compartment while the motor is running is impossible.

Just my opinion-It really sounds like a major vacume leak, but I cannot find anything at all. I plugged everyhole in the carb, even unhooked my brakes and modulator and plugged the intake. Nothing makes any difference at all. It runs the same.

I'm about ready to throw this thing threw the wall!