off topic, but mabey someone can help me.

Model Railroader General Discussion (Model Railroader)
1

this is off topic, but any help would still be apreciated.
for the past 2 years or so me and my neighbor have been working on a low-budget race car project. (super x class, waterford CT speedbowl) the car is an 80’s oldsmobile cutlass suprieme, with a 1970’s 350 rocket V8 with a 4 barrel carberator. the car just raced for the first time in months, and has a MAJOR vaccume leak somewhere in the intake manifold or carberator. we have done everything we can think of to stop the leak, but the engine is just running way too lean. does anyone have experience with these motors? if so, what could be leaking?
Thanks
GEARHEAD426

2

Have you checked that all the hoses are in good condition? Often you’ll find that one of them is the culprit. Also, does the car have power brakes? How are they working. It could be the vacuum hose to the booster, or a bad booster diaphram.

I’m assuming that you’re sure it’s a vacuum problem, and not a bat jet or something?

Cudaken might also have some suggestions. From what I’ve gathered, he knows a bit about this sort of thing.

3

After checking every little hose, fitting, etc … and you are sure about the jets, etc … did you change the intake manifold? It may be leaking itself. Does the engine run worse at a certain temperature? Anyway, do you know how to check for leaks in the manifold and other places with a propane tank and a hose, etc, while the engine is running? Or even with a can of spray solvent?

Greg

4

Quick fine is STARTING FLUID or WD40. Let engine idle and spray around the POSSIBLE leaking area.

My thought would be the Carb Base and mount.

Now th racer 101 list.

  1. Intake manifold is tight to the cylinder head and since it is a race engine you are using GAP FILLING Fel Pro gaskets.

  2. Carb base has been on a piece of glass to see if it is warped.

  3. Intake manifold has NO connections to it PERIOD. Your vacum Advance (why on a race engine anyway) is coming off a tap at the BASE of the carburator.

  4. ALL connectioin to the intake have NON harding Permatex to seal the threads.

  5. You have put a try block (MACINEST ANGLE) on the Carb Mount on the intake to see if it is warped.

  6. All else fails replace the intake assy.

5

If you’re using a quadrajet gasket with the small long cutout in front of the primaries, that’s likely your culprit. That’s a Chevy only gasket, and was used with the exhaust crossover on some of the 60s and 70s engines. It will leak like all hell on anything but a Chevy. You will not be able to find it with the wd40 method, either, because it is leaking from inside the carburetor base plate. Also, if you ARE running a quadrajet, make sure you’re running an Olds quadrajet. They have the fuel inlet pointing straight ahead like a pontiac. Only the Chevy had the inlet pointing toward the passenger side. The base plates on all of them are a little different, and a vacuum leak could result if the wrong carburetor is used.

6

And I thought I was the only Olds sicko left after all of these years! I used to run the snot out of my '76 350. Great engine, tons of torque. Glad I still have it, just need a body to put it in! I had a problem like you are describing after I had to get the heads redone after I overheated the motor. Olds uses a crappy “bathtub” style, one-piece metal intake gasket/ valley pan. I was told the idea was to keep hot oil off the bottom of the intake and help keep the air charge cooler. As long as everything is within factory specs (head angle in relation to the block and intake, deck height to the crank, etc.) it will seal and work fine. If anything changes, particularly if the heads have been milled and they were slightly angle milled, or if the block has been decked, they may not seal worth a crap. My problem was that when the heads were milled they had been a little warped, so the guy gave them a slight angle milling. This changed the intake to head surfaces from being parallel to being at an angle, and the gasket would not stay sealed. I might also add that the motor had to be good and warmed up to show my leak. Anyway, once the leak was finally found by a good friend of mine, we came up with normal composite gaskets for the intake. I think they were Fel-Pro, but this was many years (and beers) ago and I don’t remember the specifics real well. Probably because I was drunk most of the time I was not at work! I can’t recall if we reused the “bathtub” gasket and added these others or not. Seems like there had to be something to keep the oil off the bottom of the intake. Hope this helps.

7

I’ve seen this many a times, retorque the intake after warm up.[:)]