Small engine trouble.

I am a pressure washer repairman, but nowhere near a small engine Braniac.

Our Sears 16hp rider won't hit a lick. The plug was ugly, but wire brushing it cleaned it. It tested good on a Honda motor in the garage. It also showed spark out of the engine in question.

But it's getting gas. It's getting spark. Even with starting fluid it won't even fart.

What the heck?

try doing a compression test.

Maybe a stuck valve if it hasnt been used or been out in the weather for some time, as post above said, check compression

Absent a compression gauge, you can put one finger over the spark plug hole and slowly rotate the crank until you feel some pressure and then turn it a bit faster. The pressure should want to blow your finger off the hole. Try not to cover the hole when the piston is traveling down. If there is significant suction, it may not feel good on your finger. This isn't a scientific test but if a valve is stuck, you won't have much pressure or suction.

Has to be good gas and adequate spark as well. Did it run last year? Has it sat for like forever? Generally a quick remove the carb and blow it out and fresh gas will get em running most of the time. Lots of small engines have filters inside the tank, they can plug up as well. Make sure the vent in the fuel cap is clear or the fuel will not flow correctly. When you say the plug was ugly, what do you mean? Sooty, oily, wide gap, etc? It can help you diagnose the problem.

Just a couple pennies worth of thought from an old fart assuming that it cranks but nothing more happens...

I figure that you're pretty well up on small engines but there are some on CPF who might not be and this topic will come up sooner or later again, so I'll go through the basics I can think of.

Is the cylinder really getting fuel (you pulled the plug and cranked the motor) or do you just smell fuel in the carb?

Is the choke working properly?

Is the deck pulley moving and/or the belt not stuck or frozen up? (Novices: don't check it until you have disconnected the plug! One hand clapping is not as much fun as it might sound)

Is there a bad or disconnected safety interlock?

Is the rest of the wiring OK? (Ever see what happens if a mouse or squirrel build a nest under a mower seat?)

Did it sit for a long time with old gas in the tank? I'll mention it for those who might not know -- if the gasoline is old it might have turned and shellacked the carb float bowl and jet(s) (as in it "gums up the works").

If it has a PTO, is the PTO clutch engaged/stuck?

Is the spark plug wire old? Doesn't have to show cracks to be no good. And is the coil good? (Once saw a picture of a guy under the hood, working on his pickup truck with his great dane leaning over the fender with his head right in there with him -- caption said something like, "Here, Fido, you put your tongue on that wire and we'll make those nasty old fleas jump right off." Not recommended but it made most of my friends laugh).

Might want to try a new plug in it (Honda small engines can be more forgiving than other brands), and is the gap really spot on?

Lastly, (since I've pretty much run through the cheap fixes I can think of - ugh - my fingers are tightly crossed) does it have good compression? Hard to kill an iron 4 stroke but it can happen.

It's a Kohler engine probably, right? You might want to check out their web site to see if they have a PDF copy of the manual for that engine. Good place to start jogging the memory.

Good luck & hope it's a cheap fix.

If it has gas, spark, and compression then it should start. I say either a broken valve spring or stuck valve= no compression.

Weird.

If it ran fine last time you used it's probably nothing on the top end or compression related. Even though you brushed off the plug, if it was that bad I'd toss a new one in there just in case. It's cheap insurance. Aside from that I'd have to guess fuel. Take the filter assy off and look into the venturi to see if fuel is actually squirting/misting.

On the other side of the spectrum, if it's flooded it's not going to start even with ether. If you suspect that it is flooding clamp off the fuel line and rotate the output shaft to the intake stroke. Hold the carb open with something that's not going to fall down the intake and use a leaf blower or portable fan to dry out the cylinder. After sufficient drying leave the fuel line clamped off and try the ether or starting spray again. At that point if there are no signs of firing then I would suspect something on the top end. The compression would have to be really low so I don't think it would be a compression issue related to the rings.

Let us know what you find out

A few more things that come to mind:

If the spark plug is flooded, then electricity can travel across the insulator of the spark plug on liquid fuel and not make any spark, even if it sparked fine outside the engine.

What color was the spark? White or blue is good, orange may not fire under compression.

If the flywheel nut loosened and the key sheared, the timing could be off. Just a few degrees can throw a monkey wrench in the works, even if everything else looks okay. When testing spark outside the engine, the spark will even look regular and steady rhythm, because the starter drives the flywheel.

Agree w/ compression test. If you don't have one, then judge how hard it is to pull the cord vs. how it used to be. If electric, you can listen to it crank, if it's cranking much faster and the starter motor isn't loading as much, then you've lost compression. I've seen a hardened steel valve seat come out of a B&S engine block. Ran fine, shut off when the seat came out of the block, never restarted.

Compression testers are ~$20 and a good diagnostic tool. If you buy carefully you'll get a leakdown tester too. The hose that runs from the spark plug hole to the gauge will be connected with a standard shop air quick-connect. Screw the hose into a sparkplug hole and plug into your air supply. This can also keep valves closed when still in the engine if you're taking the springs off to put new seals on the valve stems.

Good luck, and please let us know what turns out to be wrong with the engine.

:buddies:

BVH said:

If there is significant suction, it may not feel good on your finger.

Click to expand...

It won't hurt you. It'll only be 4 pounds of pull or thereabouts. I did the math once and then put my finger on the intake for my air compressor when it was running. It didn't even hurt.

It has sat for months not years. I would CERTAINLY have put in a new plug had I HAD one.

I'm pretty sure it was white spark.

The plug was gooped. Maybe carbon buildup.

It SOUNDED like it was cranking the same as last time I heard it.

Will try a spanking new plug tomorrow evening, along with testing compression (there is a tester around here somewhere).

Thanks for so far!

Google "reading spark plugs" and look for a site with pictures and explanations. Sites like theultralightplace.com (under their Rotach engine pages) and NGK have one. Lots of good information to be had for diagnosing 4 stroke engine problems by just comparing the plug to the matching photo. Certainly ought to help point you in the right direction.

Again, good luck.

It lives.

It had some NASTY SPOOGE in the carb.

A really clean plug from our other mower got nasty in a heartbeat.

I need to take the carb off and really clean it but at least it lives again!

Glad it works now. Good work on a relatively painless fix. You might want to hit it with some GumOut.

Now that it runs, time for fun mower memories -- I recall a neighbor many years ago who had an air cleaner problem. A small bee's nest. Want to guess how they found out? It was not my definition of "an easy fix." Could have been worse I suppose -- imagine if it had been a large comb and full of honey?

PlayboyJoeShmoe said:

It lives.

It had some NASTY SPOOGE in the carb.

A really clean plug from our other mower got nasty in a heartbeat.

I need to take the carb off and really clean it but at least it lives again!

Click to expand...

It must have been wicked if even starting spray didn't work. I can't imagine it being so bad that the venturi wasn't opening but maybe the starter spray was bad?...dunno. I use Sta-bil in fuel systems that don't get used much or drain them in cases of longer storage. That might help in the future.

It hasn't got a chance of getting bad from about mid march until early November in these parts!

The replacement gas was Stabil'ised but not what was in the carb.