Question about knocking that coming from the motor

[SteveJ]

Correct. It's 8 degrees at 750 RPM.

It doesn't take much in the way of tools to set the timing: metric wrenches, inductive timing light and tach. You can find a book on Holley carburetors on Amazon. That should tell you how to set the floats to get rid of the rich condition. Of course, cylinders 3 & 4 will probably have to be richer than 1 & 6 due to the design of the intake. Don't forget to look at your plugs. Compare them to this chart.

[FastWoman]

Zed, Gary, the loud tapping sound is metal against metal, or at least it was on our 318 inboard (#1 cylinder -- front left -- isolated on the exhaust riser, sort of like the #6 on the L26 exhaust manifold). I doubt the noise could have been made any other way. I figure with the gasket gone, the manifold probably hovers in very, very close proximity to the head, so it wouldn't take much movement for the two parts to clatter. The sound travels through the boat, somewhat like a prisoner tapping morse code on the water pipes. (The motor/transmission mounts are solid, not rubber.) I'm not saying all (or even most) exhaust leaks sound this way, but rather that a loud tapping sound can be due to the manifold banging/clattering this way.

Ed, the rear-most cylinder is probably the most common location for exhaust leaks in the L24/L26/L28 engine. You should look for the soot, like Gary suggested. You can also feel for leaking exhaust, but be careful. I suppose another way to check for exhaust leaks might be to use a vacuum cleaner discharge port to back-pressurize your exhaust (cool, non-running engine). Then you can feel all around the exhaust manifold for air leakage.

Incidentally, I had an interesting "EGR" issue with my Z. I had exhaust leaks adjacent to intake leaks, so my exhaust was being sucked back up into the intake. THAT was interesting!

Ed, I have to say I'm surprised nobody knows how to work on Z engine with a Holley. Geesh! It's not like it's a spaceship or anything. I guess mechanics nowadays need OBDII diagnostic codes to fix anything. Maybe you need a mechanic who's at least 45 years old, preferably at least 50. Either that, or you need a mechanic who works on classic cars. Even someone used to working on old Camaros and Mustangs should be able to figure your car out.

That said, I'm finding that the Holley isn't an easy carburetor. I just rebuilt the one on our boat and was frustrated by it popping a couple of fuel leaks that had to be brazed closed. I'm still waiting on a little piece of rubber that wasn't in the rebuild kit -- the accelerator pump check umbrella thingie that I've estimated is literally worth at least 3 times its weight in gold. (No kidding.) Compared to other carbs, the Holley isn't an easy beast. It's cheap to buy, but you pay for it later. I don't think I ever want another. An Edelbrock is a nice piece of equipment, though.

[FastWoman]

PS Now that I think about it, I suppose the tapping sound could be the manifold against the nut/bolt.