Engine Run On

[elanern]

My 1970 Elan S4 (Federal) with Strombergs runs on after I turn the ignition off. Timing is at 7 BTDC at idle. Carbs are rebuilt, fuel tank cleaned and sealed. Idle speed is between 950-1000 rpm. The car had been sitting since 1996, I started the renovation about a year ago.

Any thoughts on what might be causing the run on and how to cure it?

Thanks in advance.

[twincamman]

welll 'run on' dieseling ,as it is called here is usually caused by excessive heat sooooo perhaps you have a'run lean' condition in the motor -ie intake leak or too lean mixture --it can also be caused by carbon build up on the piston causing a high compression or diesel like firing of the fuel with out spark ----- ed

[Chrisrich]

Ernie, I also have a federal '70 with strombergs, that occasionally does the same thing.
If I give the throttle a stab before I shut it down it does not happen, although I understand you might be looking to get to the root cause....

Chris

[elanern]

Thanks for the replies so far.

I don't think I have an air leak - new gaskets, new o'rings, the vacuum lines to the bypass valves are plugged, and I'm fairly certain the one-way vacuum connection to the headlight canister is not leaking. I am using the next richer needles from stock, and the float levels are spot on.

I guess carbon build up could be a possibility, as suggested. How to best clean up the combustion chambers is the next question. What have folks had success with, short of removing the head to decarbonize? I'm thinking something like Seafoam, poured into the cylinders, and left to soak.

Again, thanks.

[types26/36]

I dont have any experience with stromburgs but can you get your idle down slightly to say 700rpm and I presume you are useing the highest octain fuel available, I have heard of squirting brake fluid into a hot running engine and reving it to try to dislodge carbon deposits and clean the pistons, I tried it once on an engine with a sticking valve and it did seem to help but it looked as though a smoke bomb had exploded with coluds smoke .......wear a mask if you try it