OutdoorKing Repair Forum Forums General Discussion Forum Off Topics question on fuel

with 2 stroke engines i was taught to turn the fuel off when finished mowing and let it starve. with 4 stroke i presumed you just turn them off.
will it do any damage if i let my 4 stroke starve of fuel to stop?

I'd beware letting a two stroke starve to stop mowing, as the engine is lubricated by the oil in the fuel. No fuel = no oil = no lubrication. I understand residual oil in the crank case will offer some protection but it seems better practice to kill the ignition instead.....

I agree, dont starve it of fuel, just turn it off and then turn off the fuel tap. Starving them runs them lean(relly lean) for the last couple of seconds and dininitely does them no good.

Do not let a 4 stroke starve - the valves are likely to overheat, and apart from that, the ones we use for mowers are always governed, so it is going to end up starving on wide open throttle, which can cause detonation with possible overheating or crushing of the piston.

I always let 2 strokes starve, except for chainsaws. Chainsaw engines are so highly tuned that there is a danger of piston damage even in the very short time they are running lean. At the other extreme, 2 stroke mower engines are, to put it politely, comparatively undertuned and oversized, so they aren't likely to develop high internal temperatures unless you starve them at high speed, full throttle. The purpose of starving them is to store them between uses without those last drops of petrol-oil mixture drying out in the carburetor and leaving a residue of sticky oil in all the wrong places. I've never seen a two stroke's crankcase bearings or bore look even slightly dry after running it out of fuel at moderate speed.

In the case of small 2 strokes without fuel taps, such as whipper snippers and chainsaws, if you have a modern 2 stroke engine design with an air purge pump bulb, by the time you pump all of the fuel out of the system when you empty the fuel tank after each use, there is very little fuel in the carburetor anyway. I find they only run for a small fraction of a second when I start them after pumping dry.

cheers mate

Correct. I've seen rusted bores, on 2-strokes whose owners used the 'run dry to stop' method.

I'd speculate that this practice may have had some point, back in the days before specific 2-stroke oils were marketed. The old Castrol XL used to drop out of the fuel, and settle at the bottom. Now, this can be rectified for the fuel in the tank, by giving the mower a good back-and-forth shake.

But that wouldn't work on the fuel in the carby bowl - if the oil layer there reaches the main jet, it'll extremely hard to start, at the very least.

Hi
I worked as a mechanic in a Victa dealership for 5 years, if your not going to use your 2stroke for some time turn fuel off and let it run dry. If fuel is left in Carbie it will evaporate and leave the oil there which can cilitify ( not sure on that spelling ) and block jets ect. If you think this runs them to lean after you do it remove the starter assy (Victa) and you will see that there is a good quantity of oil residue still within the crank assy. Also if your fuel goes off its only the tank you need to drain.