Engine diesels.

[1lo620]

What causes engine to diesel after turning off. And what can I do to fix. 

[datzenmike]

As you know, dieseling is the heat of compression igniting the idle mixture. You need heat and fuel.

 

L20B carburetors have an idle cut or anti dieseling solenoid that allows gas to the idle circuit when the ignition is on but shuts off gas when the ignition turned off.  No fuel... no idle. So if you have replaced the original carburetor with a Weber that doesn't have one this is probably the reason.

 

 

Other causes of dieseling on shut off...

 

1/ Idle is set too high and engine is running on the primary barrel. The idle cut solenoid has little effect as you are getting gas from another source. Fast idle can simply be the idle speed screw it set too high, from too tight a throttle cable, fast idle cam stuck on, BCDD out of adjustment.

 

2/ Choke is not shutting off fully so a rich mixture is the result. Idle cut if you have one, will not have much effect for the same reason above.

 

3/ Fuel bowl over filling and flooding. Gas runs down into intake. Idle cut has little effect. Causes of flooding can be float set too high, hollow float has filled with gas and sunk, inlet needle valve blocked from closing by dirt.

 

4/ If no idle cut is on your Weber, dieseling can be from...

Engine running too hot or over heating 

Spark plug heat range too high.

Too high a compression for the octane rating of the gas you are using.

Extremely carboned up combustion chamber

 

 

Until fixed don't allow it to run on or diesel. What I do or have done in the past is stop, hold brake firmly, let up clutch pedal so that the engine lugs like it's going to stall, turn ignition off, wait till engine stops completely, let clutch up all the way. Three or four times and it becomes a learned response and you do it automatically.

 

 

 

 

[Stoffregen Motorsports]

Does it have a Weber? Weber DGVs are notorious for dieseling. Later DGVs had fuel cutoff solenoids that solved this problem.