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I have a 1969 l46 that was reported as “warmer than stock” when I bought it. I’ve been enjoying it and doing the wiper system and other things to it. Lately it has developed a miss. It seems like a cylinder quit and runs rough. It starts and drives but defiantly not as it had.
I pulled the plugs and they look terrible. I’m sending the carb to Lars today to eliminate that possibility. Now I’m a little confused on the lack of a vacuum advance on my distributor. There even isn’t a spot on the distributor itself for the vacuum line to go into. What do I have?
Some distributors don't have a vac advance. And some people remove the vacuum advance. On a street driven car, you want the vac advance. As long as your distributor has the mounting mechanism, I would add one.
My reccomendation would be to get an adjustable vacuum advance cannister and the Crane or MSD advance limiter plate. An adjustable cannister lets you control how much vacuum is required to get max vac advance, the advance limiter allows you to control HOW MUCH advance is added at max vacuum. This lets you really dial it in so you don't have a wandering idle due to varying vac at idle, and make sure you don't have too much timing at cruise when you are at maximum mechanical advance.
Run compression and leak down. That’s a lot of oil on the plugs. Could be valve seals, rings, bad gaskets. New plugs won’t sort that out. How old is the motor? How many miles?
I just did a compression test and the results were 160 -+ 5 across al cylinders with the compression increasing at the same rate during the test. The new plugs with 20 minutes of run time did show traces of what I think is oil. What’s next? Valve guides?
if compression test pans out good, check your exhaust, comparing any residue can help point to weather issue is oil or a rich condition from carb. by the time fuel makes it way through the cat the residue is usually more of an ashey color whilst oil tends to leave a darker deposit
basically its oil or a rich fuel mix at this point, I cant rem about your year but something about the vacuum and trans fluid comes to mind, somehow getting sucked into the engine through the modulator, im sure someone else has a better memory on this then I do.
edit im not saying take apart exhast, just use a cloth swab attached to a wire and test like 10 inches or so from the exhaust tips
Since the compression test indicates no significantly low cylinders, then valve stem seals are the most likely the problem, especially if the engine has many years on it. Fairly simple fix.
I would also check the vacuum advance with a timing light and be sure you are getting total advance.. The unknown distributer could be performing the advance, but a vacuum canister on the distributor will give much better street driveability.
Running rough
