Guys,
I'm selling my 7 on Friday and suddenly have a vacuum leak, I think. The car runs like *** at anything less than full throttle, but I'm running a Holley, so there's not nearly as many options as to where the leak might be. My problem is that I've got final exams right now and don't have much time at all. On a Holley w/ 4-bbl RB manifold, the vacuum tap is on the rear primary runner. Do the front and rear primaries have a circuit that allows them to share vacuum? The reason I ask is that the car sounds like it runs on one rotor when at idle and partial throttle, so I was thinking about unplugging the coils, that way if I disconnect no. 2 and the idle doesn't change, I know that the leak is somewhere on the vacuum accessory circuit (just cruise and brakes). Any thoughts? Where's the best place to look for a leak? I did a 5-minute flashlight-powered walkaround and didn't notice anything obvious.

 

bump. I'm in a bind here. Any ideas?

 

At anything less than full throttle doesn't sound like a typical vacuum leak. Perhaps the float level is wrong and lets too much gas in unless it's floored.

Isn't that really easy to adjust on Holleys?

 

Well, the car ran great 3 days ago, then I changed the water pump and washed the block off (getting rid of excess antifreeze) and it suddenly runs like ***. I wouldn't think the float level would mysteriously change, but I'll check. Any other ideas?

 

You changed the waterpump? Do you have to unplug the OMP line(s) from the bowl(s)? If so, did you remember to hook them back up? I'm sure you did, but I've gotta ask.

 

Yeah, I replaced the OMP lines. To check Holley floats, do I have to take the bowls off the carb base?

 

On a Holley w/ 4-bbl RB manifold, the vacuum tap is on the rear primary runner. Do the front and rear primaries have a circuit that allows them to share vacuum?

No, they are 4 seperate runners.

Yeah, I replaced the OMP lines. To check Holley floats, do I have to take the bowls off the carb base?

No, you remove the sight plugs. The fuel should be at the bottom of the hole.

Well, the car ran great 3 days ago, then I changed the water pump and washed the block off (getting rid of excess antifreeze)


I bet you got water in the dizzy. Did it run crappy right after you washed the engine? I bet its ignition. Owner induced. Pop the dizzy cap and check it out.

 

Will do. And the float level is right at the bottom of the RB OMP tap, so that looks right.

UPDATE

Well, I checked the dizzy, and there's nothing anormal there. If I can keep it at 2,000 rpm, it'll backfire 3-4 times a second, so the mixture's screwed up something bad, I'd think. I've capped off and sealed the vacuum port on the rear of the manifold, and still nothing. Any idea what's up?

 

Cap and rotor are now new, as are spark plugs. Nuthin. Ideas?

 

I took the aircleaner off and ran the engine, looking down the primary bores at roughly 4k rpm. It looks like the no. 1 is flowing a little less than no. 2. I dunked both floats by slipping a small screwdriver in the peephole and OMP hole, and both are adjusted just right. Is it possible that I have debris in the primary no. 1 circuit somewhere? It's always been run with a fuel filter, which is relatively new. I doubt I'd have inadvertently changed the mixture in the course of washing it, but have never tuned a Holley, just dropped this one on so I could sell the Dellorto.

 

Just so y'all know, I took the Holley down to rebuild it and discovered that the 1 and 2 idle adjustment needles were 2.5 and 4.5 turns out, respectively. Any chance that two turns would make a hell of a lot of difference? I have a feeling I'm not gonna need to rebuild it and that these damn needles were the problem. I can't fire up the car until Saturday, but wanted to see what y'all had to say. Likely problem???