105 won't start low compression stale gas what do I do first?

[MrChic]

Ok, so I really don't know a lot about tractors or engines. I have done some pretty big auto maintenance though like ball joints and rebuilding a Bronco front end, so I think I can learn. I got my choke cable done finally last night and started looking at other things. I can't get it started even with starting fluid. Turns over no problem, but won't start. She has been sitting for 2 months so the gas is probably stale. So I started draining the old gas, took of the sediment bowl and drained at the petcock. I still have to get fresh fuel so I start looking through the service manual and read about a compression test. So I do one. 65-70 psi. Uh oh!! Spark plug is real sooty looking. Where do I start? The Kohler seemed to run well last time it ran. No noticeable smoke or odd noises. Could carbon build up on the head or something else cause low compression, or is it definiyely time for new rings or a possible rebuild? Sorry this is rambling but I get "Cub time" in fits and spurts, so I am trying to take advantage of a few hours this week.

[Yosemite Sam]

98% of all carburetor problems are electric. First thing, check for spark.

You are going to get a low compression reading because the Kohler motors have a compression relief system built in, otherwise the S/G wouldn't turn the motor over fast enough to get it started.

Don't get me wrong, yes you probably should clean out the fuel system, but the first thing I always do is check for spark. Then work backward from there.

And yes, the carbon should be cleaned out of the combustion chamber at least every couple of years (depending on use) but that probably isn't going to keep the motor from starting right now.

[MrChic]

So to check spark, I pull the plug out of the engine and lay it on the block and turn off the lights right? Turn the engine over and look for the spark across the electrode? Then followw it to the coil, then points? Is this in the service manual, or just general knowledge? I am going out right now to check for spark.

[MrChic]

What is the procedure for checking spark? Sorry, I am really that uneducated about all this and I want to make sure I am doing things correctly.

[Yosemite Sam]

I've got a little gadget that I got at Harbor Freight for about 2 bucks that goes in between the plug and the wire, it lights up each time the plug fires. But yeah, remove the plug and ground the end to the motor and turn it over, while looking for spark.

Normally, when I get a new to me old Cub, I check the battery with a test light to see if there is any life in it, if the light burns bright the battery is better than if the light burns dim, not dealing with rocket surgery here... If it's dim or doesn't light at all I unhook the battery and get a boost box and hook up to battery cables. Turn the key to the "run" position, then using the same test light I check to see if there is power to the coil (small lug +) if there is then go to the other side (small lug -) then turn the motor by hand to open and close the points (test light will go on and off as points open and close while touching test light to the neg. side of the coil). Turn the engine till the points close then open and close them with your finger or screwdriver and watch for spark between the contacts of the points. If you have power to the end of the wire where it hooks to the points but no fire between the point contacts then file the points a little and try it again, you will probably want to check the point gap, especially if you have filed them. If you don't get a light at any of these steps then you have to go backward from that point, and you will usually find a bad wire or bad ground.

Some of the guys will argue that you need a volt meter to check volts and resistance and that I don't know what I'm talkin about, but this method has never failed me yet, if you get fire to the points and a decent fire at the plug then this should be good enough to at least get the motor started. After the motor runs then check volts and resistance and replace/repair parts as needed.

One thing that I'm sure the guys will agree with me about is, if you don't get power to the places that you need power to, there are three very important things to do.

Check your grounds, Check your grounds, and Check your grounds.

[ol'George]

FWIW.
Sometimes a spark plug can short down the center electrode appearing to not have any power getting to it.
If you stick a bolt or screwdriver in the plug wire boot and position it close to say the head, and look for a spark as you crank it over, that will tell you if or not you have spark.
I taught small engines to my 4H kids for a few years, and one time asked them if a engine would run without a carburator? of course they said no!
Wrong I said, and I proceded to remove a carb from an engine.
then I sprinkled a little gas in the intake port with a spray bottle and cranked it over and it ran.
of course it ran as long as I sprayed a little gas in the port.
Yes, the rpm was uncontrolled but the fact remained that the engine continued to run.
3 things are needed:
Air,
fuel,
and ignition, at the right time.
if you approach the problem with those things in mind.
usually it is quite simple to find the problem.

[Yosemite Sam]

ol'George,

I agree, I think sometimes we unintentionally make things more complicated than they really are.

[wshytle]

MrChic-

You might also ohm out the coil wire. I recently had one bad on a tractor and it drove me nuts. I finally decided to ohm it and found it broken. It's not an everyday occurence but it happens.

Wayne

[Rhoderman]

I'd suggest pulling the plug and laying it on the head and spinning it over. If you see spark, dribble a teaspoon of good gasoline down the spark plug hole. Put the plug back in, connect it, and see if it will fire with the choke open and at half throttle. If it fires a couple times and quits, you probalby don't have fuel flow. If it doesn't fire, you might have a weak coil (or plug wire like whystle says) where the compression kills the spark.

I haven't been having much luck with starting fluid lately. Probably someone made it safer by making the stuff less volatile or something. I was trying to start my 126 the other day and after spraying a bit in the carb, I had to spin it over a long time before it fired at all. Even then it was very weak. I seem to remember starting fluid being better than this. Does it get old with time? This was some Napa stuff that is probably more than 5 years old. With real gas, it should always fire at least a couple times.

Good Luck! Your compression doesn't sound that bad since you were probably operating the automatic compression release at starting speeds.

[Merk]

The first thing I would check is the battery. The battery may turn the motor over....it still needs current to fire the spark plug. The starter will hog the most current....sometimes leaving little to no current to fire the spark plug. The age/condiation of the spark plug has plenty to do the spark plug's performace. Best thing to do once a champion plug is fouled is replace it. An Autolite 215 spark plug is a good plug for your Kohler motor. A new points and condensor may needed.

The fuel system-carb, sediment bowl and gas tank may need cleaned out.

Best thing you can do all you small motors is go to a 30 gas rule. Any gas (2 and 4 cycle ) in my storage container that is 30 days old is add to one of my autos. I will add a fuel stablizer to my storage container before I add gas to them. Two good stablizers are Sta-Bil and the one that Briggs and Stratton sells.

I don't used starter fluid. Gumout carb cleaner works great.