Small engine head scratcher

[axisg]

Looks like a little capacitor off the side of the motor. It has given me the run around more than once

 

[Bonnewagon]

the mower hits something with the blade and stops suddenly,

Been there- done that. The rarest thing is for someone to admit hitting something hard. The blade/shaft/piston stops short but inertia keeps the flywheel turning. That shears the key and advances the timing. The symptom is backfiring and trying to run backwards. That often breaks the pull-start which can not go backwards. EZ fix to yank the flywheel and replace the key. Hard part is finding a new key for a 30 year old engine. But none of that happened. They just would not start. All the normal fixes had no affect. I mean it's a lawnmower. Given a clean carb, fresh spark plug, fresh gas, it should run and run great. Nope. It was not until I filled the dry crankcase with oil. The only kill switch on the magneto ignition is the one that is rigged to the pull-bar up on the handle. You have to hold the bar to the handle other wise it grounds the magneto and there is a brake shoe that stops the flywheel from turning. I have taken these engines apart and there is no oil-float switch that would kill the ignition. Oddly, after running with hardly any oil for who-knows-how-long- the engine did not smoke or show any distress. It still runs great.

 

[pontiacgp]

Mark, if you figure that one out maybe you can explain this one. My son has an ATV honda wanna be, it would only start after constant cranking and alot of times it needed a boost. He changed the oil in it and it starts up real quick now every time...I called BS on it but he insists that is all he did......

 

[Bonnewagon]

Steve- same thing as me. I even contacted my Enginerd Cousin. He proposed that since the oil is a splash type system, then since no oil was getting to the rings, and the engines are old, then perhaps compression suffered enough to not suck the fuel/air mix in from the carburetor. But I countered that if the rings were that worn the engines would be smoking like crazy. I remain stumped.

 

[pontiacgp]

the ATV my son has had oil in it and it wasn't low and with the new oil it doesn't turn over noticeably faster....and I don't know what kind of starter it has but I was shocked that starter did not burn out

 

[NJ Longroof]

OK, I have been fooling with small engines my entire life. Lawn mowers, outboards, snow blowers, mini-bikes, weed-wackers, 2 cycle and 4 cycle. This has me stumped. My daughter has two mowers at her place, a self-propelled Troy-Built, and a walk behind Sears. Neither would start. Sometimes the Sears would start, run a couple of minutes, then die for the rest of the day. I started on the Sears because it actually showed life was easier to get at stuff. I cleaned the jet. Nothing. I re-built the whole carb. Nothing. The primer pumped fuel just fine. I tested for spark and it was solid every time. Changed spark plug. Nothing. WTF? So I have an old power washer I saved by replacing the carb with a spare mower carb I had. The Sears and the PW had Tecumseh engines and identical carbs. In fact the carb I used was from the same model Sears mower so a logical test piece. I put the PW carb on the mower. Nothing. I put the mower carb on the PW. Bango! She started and ran great. So both carbs ran great on the PW but the mower stayed dead. Now I am getting pissed. I am looking at everything now and that was when I realized it was making a squeeking sound when I pulled on the rope. Just for the hell of it I check the oil. OMG! Empty! I A-ss-u-med there was oil- there was not. But OK- that would not keep it from starting. It would cause it to break, but it should run. Well I filled it with oil and tried it. The $#!^%&* thing came to life! WHY!?! I never heard of a low-oil-moron-proof-cut-off feature. I cut my whole lawn and it never faltered like nothing was ever wrong. Then I went to the Troy-Built and checked the oil. EMPTY!!! I filled it with oil and it started right up! WTF?!? The PW that worked was low too but not dry like these mowers. So OK mechanical type guys- why is this? Since when does no oil cause a no start condition?

Some small engines do have a low oil cutoff sensor/switch

 

[Bonnewagon]

Some small engines do have a low oil cutoff sensor/switch

30 year old engines? And what does it interupt? The magneto? I really want to know.

 

[NJ Longroof]

Dont know when these started showing up on small engines or if that is this reason but saw this pop up on a couple forums

 

[Bonnewagon]

That looks like a super idea. But neither of these have anything like that. Last summer I busted up a 3.5 Tecumseh because the governor broke off inside. I just wanted to have a look-see. Nothing like that was part of it.

 

[Turbo Zach]

I don't know about the engine you have, but some of the bigger engines and ATV's need a certain weight of oil to run correctly. The small engines that use hydraulic lifters. No oil or too thin of oil and they will not pump up and open the valves correctly. Fuel in the oil will cause this. Koller engines have a problem with that. Did you check to see how much compression you had before it started? You need at least 80 psi to run.