Stopping the engine: decompressor or fuel cut-off?

[jamie N]

Just an idle muse really. On my engine I've both, which are as easily accessible as each other, and both used.
However, is there any reason to have a preference for one over the other as in terms of engine longevity, or anything else?

 

[NickRobinson]

Do you mean fuel stop on injection pump? This is the correct method.
Decompression may flood the bores with neat fuel.
Stopping the flow of fuel from the tank could introduce air.

 

[Plum]

Do you mean fuel stop on injection pump? This is the correct method.
Decompression may flood the bores with neat fuel.
Stopping the flow of fuel from the tank could introduce air.

+1 agree

www.solocoastalsailing.co.uk

 

[rotrax]

In real life, stopping an engine, petrol or diesel, with a decompressor will not 'Flood' the bores with neat fuel. Even if stopped at high RPM the injected or carburated fuel will go out of the exhaust valve. Some fuel will remain, but not a significant quantity.
Many older Lucas Magdyno equiped British motorcycles had no other way of stopping the engine than an exhaust valve lifter. The exhaust valve lifter was often used on trials bikes for decending hills in slippery conditions, better control was obtained this way. This never caused problems, even on long decents and releasing the valve lifter never caused flames or backfires as the fuel had already gone out of the exhaust port.
With a diesel there is not enough room in the combustion space for the bores to be 'Flooded' with neat fuel. Also, an engine is normally stopped and is at normal operating tempreture. This is enough to evaporate any fuel residue once stopped.
IIRC, a 1920 Bollinders two stroke hot tube semi diesel I was involved in years ago only had a decompressor to stop it. That engine is still being used today.
I have 60 years practical experience as a small engine mechanic. Small is qualified as under six litres.

 

[Refueler]

Fuel Stop.