Engine running on

Post by **Onne** » Mon Feb 05, 2007 12:59 am

Every now and again my engine keeps running when I switch off.

That is, it tries to fire up to three times, sometimes the last attempt goes away with a hiss. This happens only when the engine is at normal temperature, not necesseraly after a long trip.

What can this be?
Can't be carbon residue, removed all that 7 days ago.
Compression too high?
Valves getting too hot?
Timing wrong?
Wrong spark plugs?
Mixture too weak?

There is not en enormous amount of back pressure, due to non existant baffles in the silencer.

Post by **Scott** » Mon Feb 05, 2007 5:25 am

All of the above (I doubt compression though) and:
Intake air leak,
Idle speed too high,
Fuel bowl float too high.

Post by **bmcecosse** » Mon Feb 05, 2007 7:42 am

Wrong grade spark plugs - timing set retarded. Advance timing till you hear pinking - then retard v slightly. Could also be cheap petrol - try another brand.

Post by **Chris Morley** » Tue Feb 06, 2007 1:47 am

Engine run-on seems to be a thing of the past for my 1098 using 95ron unleaded & Castrol additive. Previously it helped if I slowed the engine idle by turning the screw, especially in Summer. However I'm not sure if your cars have one!

Post by **Onne** » Tue Feb 06, 2007 1:57 am

But I always thought one should use high octane fuel in higher compression engines?

I currently use Shell Vpower or similar with lead additive.

The weird thing is this all started after grinding the valves in, thus improving the compression!

My Series II has full 1098 runnin gear, I'll take the idle down a tad

Post by **bmcecosse** » Tue Feb 06, 2007 7:43 am

Did you take all the little sharp edges off the combustion chamber walls/beak/valve edges ? Running on is caused by something glowing red enough in the chamber - to keep the ignition cycle going. This can happen with wrong plugs/sharp edges/carbon deposits - and mainly through running with ignition set too retarded.

Post by **JimK** » Tue Feb 06, 2007 11:39 am

You say about the ignition set too retarded. Mine's doing it a little, and I've just noticed that the dizzy vacuum pipe is split.

It runs fine with some throttle but idles badly; as the vacuum advances the timing a bit, would the lack of vacuum advance cause a bit of running on and a not-terribly-good idle?

Post by **bmcecosse** » Tue Feb 06, 2007 1:07 pm

Yes - absolutely. Double whammy - because it also introduces a small air leak into the inlet manifold !

Post by **JimK** » Tue Feb 06, 2007 1:17 pm

bmcecosse wrote:Yes - absolutely. Double whammy - because it also introduces a small air leak into the inlet manifold !

Doh! Of course it will, I hadn't thought of that bit.

I might have enough slack to cut off the split part. Have to have a look.