[The Scifi Guy]

For me, for 30+ years, the leaks always developed at the 6 intake/exhaust-to-head bolts. Usually just an 1/8 to 1/4 of a turn of those bolts did the trick. You have to tighten them about once a year when driving daily. Don't overtighten them or the heads will snap off when the exhaust gets red hot. The factory torque spec on those is about 10lbs lower than would be normal for bolts that size because of that exhaust expansion problem. The low tightness contributes to them unscrewing. If you end up removing them, add a little red Loktite to them upon reinsertion. The heat will burn off the Loktite, but it will help to gum up the threads and dissuade them from unscrewing so easily. There's a headpipe-to-block bracket that many Opeler's cars are missing that helps keep the intake/exhaust from wiggling up and down and encouraging the bolts to unscrew. It looks like this:

I'm not a fan of used carbs. You have no idea how many miles are on them and what rig jobs the previous owners did to them. For peace of mind, put a new one on, then you rule out every one of the 25 different carburetor-related problems that can cause you grief.

If your carb throttle shaft is leaking bad enough that it's affecting your engine, the carb is probably shot.

Based on what you said about your spray test, it's more likely that you're leaking at the carb-to-manifold gasket. You can regasket and/or you can try a quicky fixy by smearing Permatex High Tack sealer all around the carb at that gasket to plug the leak. If it works, then that was your problem and you now know you simply need to do a commonly needed regasketing. When I drove daily in my GT for 18 years, I would need to redo the gasket about every 5 years.

A somewhat far-fetched cause could be a leaking brake booster or hose. They're just a giant rubber diaphragm inside a tin can. And they're 50 years old. Not too many rubber things can last 50 years without degrading. It's a pain to remove the hose to test them though, you would either need to disconnect the hose from the one way valve and try blowing into the hose to see if it leaks or remove the hose at the booster and fasten on a temporary hose to blow through. A simpler test would be to clamp some vice grips on the hose immediately after the vacuum tree and see if that changes the engine behavior. Or try just aiming your carb spray at the vacuum tree to see if that makes the engine misbehave.

If you have an automatic you may have a leak in it's 1/4" hose also. Same deal, clamp the hose near the vacuum tree and see if that changes anything.

 

[The Scifi Guy]

A few years back I also had a hidden leak caused by a cracked plastic T-fitting I had spliced into a vac line. The crack was on the bottom of a black plastic fitting where I couldn't see it and a black crack on a black fitting was hard to detect.

Don't buy plastic fittings if metal ones are available.

:veryhappy

 

[The Scifi Guy]

I don't think he's spraying the cleaner INTO the carb. He's spraying it at various locations at the hoses, manifold, and OUTSIDE the carb in order to find out where it's leaking. Therefore, he would want something that doesn't combust and WILL gag the engine if it inhales it. He could spray Windex if he wanted to, as long as it's presence in the air/fuel mixture, should it get sucked in through a leak spot, disrupts the combustion in a noticable manner.

:veryhappy

 

[The Scifi Guy]

I never liked those vacuum trees on a GT. The close proximity to the heater box forces a sharp bend in the brake booster hose, which can cause it to leak. Other Opel models have way more room in that area. The last time I had a stock manifold I removed the tree, tapped the hole to the closest NPT thread, and screwed in a big T-fitting from the hardware store. Then I added various reducers and barbed hose fittings for the 3-4 things that needed vacuum(Brake booster, vacuum gauge in the dash, and auto tranny modulator. My engine didn't need vacuum advance.) Now the brake booster hose ran straight to one side of the T and the other side of the T went to the auto tranny. I spliced a smaller T fitting into the auto tranny hose to feed my in-dash vacuum gauge.

The nice thing about the vac gauge in the dash, where the clock used to be, was that it would let me know if a vacuum leak was starting to develop, which would happen about once a year when I drove the cars every day. I had a vacuum gauge in all my GT's for 30 years, including the wiz bang GT I have now.

:veryhappy

 

[The Scifi Guy]

The screwing in or letting out the idle mixture screw had no effect on the engine timing.

Probably you misspoke, but, of course, turning the idle screw wouldn't affect engine TIMING. You probably meant to say "engine running".

Go back to whatever the baseline idle speed and mixture screw settings are supposed to be and maybe fiddle with the dizzy to adjust the timing to work with things at those settings.

:veryhappy

 

[The Scifi Guy]

As for the ball on the flywheel, I am convinced it is not there. Using my finger, I felt the flywheel through a complete revolution trying to find it. I have read that they can fall out, but there seems to be no hint of where it was located.

Unless stick shift flywheels are different that automatics, it's not a ball that you're looking for, it's a round-ish indentation. So nothing to "fall out". The pointer pin in the bell housing opening could theoretically fall out. When you find that round indentation hole, put some white paint in it. I just now went in my basement to take a picture of it from one of my automatic flex plates and I too found it difficult to find(and mine was marked with white paint and it still took me a while to find it):

(Oh, I see by Manta Rallier's pics that the flywheels are very different. They're one big thick hunk of metal. My auto flex plates are a gear wheel welded to thick sheet metal. Hmmm.....wait a minute....I don't know what the heck is going on with the flex plate I took a pic of. The flex plate bolts to the engine at the 6 center holes and bolts to the tranny's torque converter at the 3 holes midway out from the center, but this one seems to have been bolted to something else at the 6 outside diameter holes. What the heck.......?)

 

[The Scifi Guy]

Whaaaaaa...?

Shouldn't vacuum be at it's highest at idle when measured at the manifold?

I have an analog vacuum gauge in my dash and when I'm idling it's somewhere around 15Hg. I've had vacuum gauges in my dash for 30 years and they always read somewhere around 15Hg's at idle.

It's when you step on the gas and let air in via the throttle that your vacuum drops to zero.

This is the VDO kind that I always used in place of the clock:

And this is the type, on the right, that is in my car now:

The needles always stand straight up at 15Hg on both at idle.

:thinking: