Dieseling

[John Hofstetter <hofs@domain.elided>]

>Subject: Detonation problems
>
>I have a scout 80 with a 1971 4 cylinder 196E cid.  The thing keeps
>sputtering after I turn it off and I cannot figure out why.  I have a
>rebuilt carb recently installed, new fuel filter, new air filter,
>adjusted timing correctly, new points, new distributor cap and rotor.
>
>Any suggetions?  Also I noticed the 196E timing is TDC and idles at
>700-725 rpm: where as the 196 is 4BTDC and idles at 450-500 rpm.  Should
>I try the other timing mark? How will that do on gas performance?
>
>Thanks for any help I may receive.
>
>Matt

Matt, 
Your engine is dieseling, which means that hot carbon in the combustion 
chamber is continuing to ignite the gasoline without a spark at the spark 
plug. Getting rid of that carbon will help. Higher octane gas will 
probably help, running a carbon ridding additive through the gas will 
probably help, pouring a carbon ridding additive down the throat of the 
carburetor will probably help. I don't think timing will have anything to 
do with it. Cutting the idle speed will probably help too. A 
one-time-at-a-time fix, is to shut the engine off with the clutch 
depressed and the tranny in gear. Turn the key off, press on the brake, 
and let the clutch out, killing the engine. Works every time, but doesn't 
necessarily impress nearby spectators. 

Howard will chew me out if this wrong, but the E on the 196E, I suspect 
means that it was an emissions motor (the higher idle is consistent with 
this). 

I would try 6 to 8 degrees BTDC on your engine regardless of what which 
it is. 

The problem with carburetion and dieseling is that the engine can 
continue to run after the key is shut off until the float bowls are 
empty, which can be a long time. 

Good luck,
John H.