Mend > Lawn Mowers

Tecumseh/Murry Lawn Mower Engine Will Not Stay Running?

I have a problem with a Tecumseh 3.5 HP lawn mower motor. I would like to know the reasoning for replacing the flywheel key. My assumption is that the key shears and the flywheel and crankshaft no longer are "connected" (ie: they each spin freely of each other). I had an incident where I hit a large rock that killed the engine but was able to restart it.

Now, a week or so later, the problem is that my engine will no longer stay running. If I press the gas primer bulb the engine starts but runs for just a few seconds. This tells me that at the very least I have good spark (ignition). I went online to verify my carburetor linkage since I had taken it off. Besides that I made adjustments to the governor but I have not had any luck keeping this thing running.

Maybe the two are not related?

The engine has run like a top for the last 23 years (yes 23) with no real problems until just now.

Thank you.

19bruman62
May 2011

Tecumseh Tecumseh 3.5 HP Garden Tools, Lawn Mowers Engine Carburetor Tecumseh

I agree - the 2 events are not connected. Sounds like a fuel blockage - remove the carb bowl nut and drain the carb. Remove the bowl and check that it's not full of crud/water. The bowl nut may also be the jet - depending on exact model. Check it's clear. If the jet is in the actual carb. you will probably need to remove it from the engine and clear it with a piece of copper wire stripped out of electrical cable.

The flywheel key is SUPPOSED to shear in the event of a sudden stop - to prevent a re-start until you have investigated the problem. On a points engine, the engine will not fire with a sheared key. On an electronic ignition engine, you will probably get a kick-back sharp enough to discourage you from trying again without fixing it! An object solid enough to shear the key is also capable of bending the crankshaft.

phil_saunders(a)bigfoot.com

Phil Saunders
May 2011

the flywheel key is needed for the timining of the engine if your engine starts and runs for a few secs the chances are the key is fine. your problem is a fuel based one as it runs on primed fuel only take the carb to bits clean through if unsure you could take it to a local repair centre and have it sonic cleaned for a few quid. beware Tecumseh parts are becoming very rare as they went bust quite some time ago.

daz
May 2011