Magnetos, compression, dieseling. Molines

mmkid

Member
I have 3 molines that I pull, all have magnetos.
403 with 4210,s, 605 with 4231s, and an 800
With 4229s. All compression ratios are fairly
similar, but for whatever reason, upon shut down,
The 605 and 800 will diesel when I shut them down
, even when running race gas, and the 403 engine
doesnt, even running on just surpreme fuel. I have
messed with timing on the 6 cyls, adjusted carb,
adjusted cam/crank timing, and still, those both always
Diesel. Both run great, sound good, make good power.
Any opinions greatly appreciated here, thank you
 
It can't diesel without fuel and air. So it's your carb. Low idle. Newer tractor's have a electric shutoff on carb jet.
 
My guess: either idle speed is a bit high, or as engine is dying, the governor is opening throttle back up. Allowing fuel and air flow enough to be ignited in hot cylinders. Most any engine will diesel if fuel and air is not shut off. I have a UTS that when I shut it down I have to push the throttle closed by hand to prevent diesling. Probably the linkage adjustment is off a bit but it runs good so I haven't messed with it
 
very easy fix, just make sure the throttle plate is close at shut down. timing is not the answer. adjust carb so when at slowest idle it will be closed and stop engine. vehicles years ago had a solenoid on carb to do this that closed the throttle plates when key was turned off.no fuel, no air, no run.
 

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