1967 3.8 Sedan

Started By: Michael Collins on 2005-05-15 07:28:39

I would please like some help with my 1967 3.8 sedan. the car will fire up o.k but when it reaches normal running temp and is switched off it will keep on running for up to a minute. I have checked the timing several times. the HD carbs where sent to JO CURTO for a rebuild. it has the pentronix ign in the distributer. the spark plugs are Champion NY9's.
I am wondering if a colder spark plug with a smaller gap would help with this problem. I also squirted water into the carbs whilst it was running to loosen off any carbon that may have been on the pistons but nothing came out of the tail pipes. I really would appreciate some help.


Hi, I have a 1965 since last November and with the same problem; It is called "dieseling". I have an appointment with my local tech to fix this problem and then I will know how to fix it in the future. But I sure don't know how to resolve it even though I can resolve most issues with my 1984 XJ-6, a more complicated car, but this one has me puzzled because the Timing is also "on the money" and the car runs beautifully otherwise, it only happens when I try to shut it down. By the way, this can cause serious damage to the engine, so I have decided to leave it alone until June when I'm taking it to someone who knows these engines. A trick to get by is to shut the engine while the transmission is in gear, in Drive or Reverse, but in my car, it just keeps dieseling even in gear. This may have something to do with the compression of the engine, which in mine is 9:0:1 or something like that.

in addition, I have noticed that the gasoline Octane has a lot to do with the dieseling. my car needs 98 octane but 93 is the highest that I can get.
And then, some 93 octane gasolines are so "watered down" that the dieseling is exascerbated. Other gasoline brands seem to eliminate it, but not entirely. Assuming the Timing and Carbs are correctly adjusted, the problem is the Octane in my experience. I don't have this problem in my 1984 XJ-6 with a 4.2 engine.

If your car is running for a minute you need to look for an electrical problem. A diesel has a glow plug so unless your pistons have glow plugs on them you are getting an ignition source from somewhere. A min. is a long time. George Camp

re: "Dieseling update". turned out to be a vacuum leak; in my car, there is/was a copper vacuum tube with a rubber splice in one end of the tube connecting to the carburetor, and a rubber elbow in the other end of the tube connecting to the ignition. The rubber elbow was cracked, so air was being "injected" into the carburetor after shutdown, and because there is fuel in the carburetor, the engine kept trying to run. Simple, but it took an experienced technician to diagnose it without even checking the car. "Check all vacuum connections" he said. (there's not many). I replaced the copper tube and rubber splices with a vacuum hose, then drove the car for 2 hours to get it hot, shutting it down at red lights to induce "dieseling", but the problem has dissapeared.