clowe1965

I've been fighting vacuum leaks for the past few months on a 68 302 reman engine. I have a 1985 302 ford IM that I machined a custom spacer for to block off the exhaust cross over, topped off with an edelbrock 1403. I first had leaks on all four sides of both the spacer and the carb, so I took the spacer off and faced both sides (it was cut from 1" plate with a mill finish). Judging from the gasket separation when I took the spacer off, I believe the surface was too smooth to allow for bonding of the gasket. I also used rtv black sealant on all mating surfaces. Anyhow I machined both surfaces and reinstalled everything dry. I put a .25-.5" bead of aluminum exhaust sealant around the IM/spacer mating seam after seating the spacer. In a further attempt to fix the leak, I also used a .25" insulating carb/spacer gasket. The idea being I can compress this gasket to fill in all the gaps. Well the bloody thing leaked on the passenger side and the rear. Pretty sure it wasnt leaking on the lower seal, given how thick the bead is going around the outside. Leaked from a cold start (it was 85 if you can call that cold) all the way to fully warm (190).

Took the carb back off without disturbing the spacer/IM seal, checked the spacer and it is flat as far as I can tell. The carb appears to be flat too. I took a magnetic level and used it as a straight edge to check, no visible gaps. Would a gap smaller than can be detected in this manner cause the leak? I would assume I could have up to .010" variation in the mating surfaces and still seal with a .085" gasket, even more so with a .25" gasket. Anybody know the limit for the flatness tolerance? Or any other suggestions? I'm gonna install a normal carb/spacer gasket to see if that solves it, but I'm not crossing my fingers.

groho

sounds like you're dealing with warping from heat, either the carb base, or the spacer, or both. consider using a phenolic spacer that shouldn't absorb heat, and a good gasket top and bottom, should address the issue.

clowe1965

The spacer is aluminum, I dont have a choice of using a different one without changing the intake manifold, allowing the exhaust crossover to vent past the side of the carb, or find the OEM plate that went there.

The leak occurs from a cold start all the way to fully warm, so it would have to be perminantly warped, but I have no indication of that when using a flat edge.

Diputado

FWIW...I'm running a Weiand Stealth intake with a 1/2" phenolic spacer under a Holley 600 carb on a 289 and have had (so far!) no leaks of any kind. Also...maybe it's just my opinion...but personally I wouldn't use rtv sealant in areas where it's in contact with fuel, as it will slowly dissolve in the fuel mix and get into the intake. I've always just used the carb/spacer gaskets "dry".

Coupe

Maybe a spray on copper coat type of sealant, but no RTV.

clowe1965

The sealant is on the outside, so theoretically it shouldnt come into contact with the gas mixture if the gasket is doing it's job. It's also an aluminum base that was left over from my header install. Kinda wish I had gone ahead and put an aftermarket intake on here. I just took the manifold off to clean out some debris from drilling too far through a runner after a thread repair job. I am sick of messing with the coolant system. Gonna try the normal spacer again, then the copper or whatever i find sealant. If all that fails then craigslist or mustang week shopping I will go.

Diputado

Hey man, Summitt Racing has brand-new Weiand Stealths for $176...it's a really good intake for a SBF!

clowe1965

Might look at that, I was looking at the edelbrock performer. I also found an airgap locally on craigslist for 150, but I can't test it until I get a new starter.

Diputado

Yeah...those Edelbrocks are also good. I've run Holley Street Dominators (single-plane and dual-plane) as well as an Edelbrock Torker 289 way back (tells how old I am!), and really like the Weiand I have now. Although you probably already know this...no matter which one you go with, if you're going to be just running on the street, go with a dual-plane...but if you're going to really wind 'er up, the single-plane would be better.

clowe1965

Let's see, 500 cfm carb......yup I'm gonna need a single plane for sure! JK. They don't make the torker any more, on to the torker II, man I'm young. Don't actually think I have a,preference, still holding out for the old one I have now to work.