Small engine head scratcher

[Neill]

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?

Many of these small engines started using phenolic (plastic) intakes for their carbs years ago, and my experience with Briggs @ Stratton engines ,in particular, is that they crack in service, causing puzzling problems.

 

[Bonnewagon]

These are made of aluminum. I had to remove it at the head because I could not get at the carb mounting bolts. What got me was the whole time I was trying o start it the spark plug remained dry. Thus I suspected a no fuel situation. Low oil would not affect the fuel in any way shape or form.

 

[pontiacgp]

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.

I think you just explained how an oil change fixed a hard start problem on my son's ATV.....thanks... 🙂

 

[Neill]

These are made of aluminum. I had to remove it at the head because I could not get at the carb mounting bolts. What got me was the whole time I was trying o start it the spark plug remained dry. Thus I suspected a no fuel situation. Low oil would not affect the fuel in any way shape or form.

It's gotten to where the first thing I suspect is, like, last year, and the year before, and the year...time to replace the carb diaphram ! I need to find out if there are more ethanol resistant ones available.

 

[Bonnewagon]

The small engines that use hydraulic lifters.

Not as far as I know. Last engine I mashed up had solid lifters. These are very rudimentary engines. The most exotic thing is the waste-fire magneto. A magnet in the flywheel and a coil mounted above the crank case. No points and it fires on the power and exhaust strokes. But that would jive with what my Enginerd cousin said. No oil on the rings would kill compression.

 

[Bonnewagon]

I need to find out if there are more ethanol resistant ones available.

I have come across quite a few engines that suffered from swollen carb needle seats. They are a plastic that swells from the alcohol. Superseded carbs come with alcohol resistant parts.

 

[Neill]

I have come across quite a few engines that suffered from swollen carb needle seats. They are a plastic that swells from the alcohol. Superseded carbs come with alcohol resistant parts.

My Briggs @Stratton carburetors do not have needles or seats, but the diaphrams in them are not holding up like they used to. Maybe the company has upgraded them, the parts place always give me new 'old 'stock ones !

 

[Turbo Zach]

Not as far as I know. Last engine I mashed up had solid lifters. These are very rudimentary engines. The most exotic thing is the waste-fire magneto. A magnet in the flywheel and a coil mounted above the crank case. No points and it fires on the power and exhaust strokes. But that would jive with what my Enginerd cousin said. No oil on the rings would kill compression.

I would have pulled the plug and stuck my finger over the hole and check how much compression it had when I seen it had spark. Now you probably will never know.

 

[Bonnewagon]

Well, it ran just fine until it didn't. No reason to suspect compression was an issue. It wasn't until I filled it with oil that it ran again so that is why I am so stumped. The test would be to drain all the oil and try starting it. I am still wondering why it didn't explode when the oil was that low.