Kohler k301 runs rich, quits under load

[ironman]

Originally Posted by red211

I do know sometimes you can get a spark when the plug is pulled but under compression it won't jump.

I kinda agree with red211

#2 A defective ignition system will cause an engine to crank over but not start. This could be due to no spark getting to the spark plug, a spark that is too weak to sufficiently burn the compressed air/fuel, or a spark that occurs at the wrong time.

An easy way to check for no spark, or weak spark, is with a spark tester that forces the spark to jump a large gap. This device may look like a spark plug but it is designed to demand a firing voltage of at least 20 KV. Another style has an adjustable air gap. Be sure to open this air gap far enough to force the ignition coil to put out over 20 KV. This is important because a weak ignition coil can easily generate enough voltage to jump a normal spark plug gap outside of the cylinder at atmospheric pressure. Inside the cylinder, where you can not see, the spark must jump the gap under compression pressure and this requires more voltage. A spark plug that fires outside of the cylinder may fail to spark when it is installed in the cylinder head.

from this link
http://www.linnbenton.edu/auto/perform/no_start.html

[J-Mech]

I have been studying the two articles mentioned. They seem to disagree, near as I can tell. There does appear to be a need for somewhat higher voltage to jump a gap at a higher compression ratio. HOWEVER, as the engine warms up and spark plug electrode temperature changes, that greater need is reduced as a hot electrode has a greater ability to carry an electrical charge. In other words, it takes less voltage that hotter the plug gets. It appears to be enough greater to overcome the added need for voltage due to the higher pressure. I want to note, that this lab test was on a stock engine. We are not talking about high performance...... so no need to go there. The above linked scientific study was done on a regular engine, and that's what we're working on here.

Listen guys..... there are two different approaches to internal combustion engines. Theory, and practical application. I delve into theory whenever I can because I find it intriguing. However, it seems, that my experience and practical application win out every time. Yes, I do concede that it takes more voltage to jump the gap at a higher compression ratio, but... from the first article it would appear that the difference is minimal. (On a stock motor.) Perhaps as high as 1000 volts, which in 10K volts, is pretty minimal. Besides, once the plug warms up it seems that it overcomes that need. If we wanted to dig into high performance, I know that with a "custom built", or performance, motor, with a significant increase in combustion pressure, there is a need for higher voltage spark. There are several other factors that play into this need outside of an increase in pressure, but I'm not getting into them in the interest of it's really irrelevant for the conversation.

My point: in this case, there isn't enough of a higher voltage required to say that if the plug fires well outside of the engine, that it won't when installed.
So, I'm going to quantify my post #9 by adding the words "in this application". I do agree with ironman on his recommendation of using a spark tester with an adjustable gap. It is the most simple way to visually see if the coil is weak. However, a simple OHM check of the coil while it's hot would also verify whether it is failing.

I'm sticking with my sticking exhaust valve diagnosis anyway.

[j4c11]

Originally Posted by J-Mech

Yes, I do concede that it takes more voltage to jump the gap at a higher compression ratio, but... from the first article it would appear that the difference is minimal. (On a stock motor.) Perhaps as high as 1000 volts, which in 10K volts, is pretty minimal.

I got the same thing as you from the article, which was it would only take a small increase in voltage to make up for the increased compression, with the gap being the biggest factor. However, "Automotive Technician Training: Theory" By Tom Denton claims that you need 4-5 kV to jump a 1mm gap under normal atmospheric conditions , but 10kV to jump the same gap inside a cylinder at 8:1 compression. So double. I've come to rely on the popular practice of pulling the spark plug out, and if I see a spark I'm good to go on electrical - look elsewhere. But if this information is correct, it may be useless except in the case where there is no spark at all. Very intriguing.

[ccollins0601]

Thanks for all the info. This forum is great! You guys are operating on a different level than I am but it's great to know a bit of the theory behind these things.

I've never taken an engine head off before. What am I looking at in terms of time/skills/tools required? I'm researching on google but thought I'd ask.

I don't have an air compressor/gun, I'll have to see if I can get access to one for the test.

I bought the 1200 after moving in December to a 2.5 acre property with a narrow, 800 foot driveway. When it ran well, the 1200 was in a lot of ways more effective than my hired plow guy - he let the snowbanks get too narrow for him to manuever with all the New England snow this year.

I have a 44 inch mower deck that needs a belt and some rehab, and assuming I can get the engine going I'll be looking for a snowblower attachement in the fall.

[j4c11]

Originally Posted by ccollins0601

What am I looking at in terms of time/skills/tools required? I'm researching on google but thought I'd ask.

Taking the head off requires no special tools,just something to remove the head bolts, but you will need a torque wrench and a head gasket to put it back together. As far as time and skill, not very much of either. Use a piece of cardboard, make some holes in it with a screwdriver and stick the bolts in it in the approximate shape they were bolted in. This way they can go back in the same hole. Don't remember if they're all the same on the K series, but on the Magnum I think the two center ones are different lengths, so it pays to keep them organized.

[Sam Mac]

Link to the tech library.

http://www.onlycubcadets.net/forum/f...splay.php?f=19

You'll find the manual for your tractor, the engine in your tractor, how to resurface the head and lot's of other useful info.

[ccollins0601]

Originally Posted by j4c11

Use a piece of cardboard, make some holes in it with a screwdriver and stick the bolts in it in the approximate shape they were bolted in. This way they can go back in the same hole.

Thanks for the tip.

Originally Posted by Sam Mac

Link to the tech library.

http://www.onlycubcadets.net/forum/f...splay.php?f=19

You'll find the manual for your tractor, the engine in your tractor, how to resurface the head and lot's of other useful info.

Exactly what I was looking for! I've spent a ton of time searching for instructions on these engines yet somehow hadn't come across this yet. Thanks!


Answering some earlier questions - flow through fuel line is good, no fuel filter but I plan to add one, there is some sediment visible at the bottom of the tank so I will need to clean that out too.

[Berwil]

Like you I had never opened up and engine before last summer. I pulled the head and valves on my 1450 and cleaned everything up. It fixed the sticking valve problem I was having. Like mentioned you will need a torque wrench and I would suggest a valve spring compressor; I used two screwdrivers on the valves.....never again. The manual has all the torque specs and tightening sequence. If you can use tools, you can do it.
Here is my thread.

http://www.onlycubcadets.net/forum/s...ad.php?t=32948

Bill

[red211]

Just to beat the dead horse on the plug spark. I check for spark the same way, pull plug and watch for arc. This method has always worked when checking. In auto mechanics class they went through the compression/resistance thing and that was why I mentioned it. My reasoning was when the bad coil I had would mess up the engine would run, although weak and crappy. Checking spark like that would have told me nothing at that stage since it was still running, kind of. A quick coil ohm should have showed the failure but at that time I didn't know the spec.
Did you check for spark when engine was dead or after it was running again? That question sounds kind of stupid but it could apply. I would still go with the valve, coil is just an easy check if done at the right time.
Dang you guys are some smart cookies!!

[ccollins0601]

Hi All,
I got back to this today after a hiatus. I pulled the head; low and behold there was a good bit of gunk:

20150322_203033.jpg

I cleaned as much as a could using a plastic scraper, brass wire brush, wide flat screwdriver, paper towels, shop vac, and mystery oil:

20150322_211958.jpg 20150322_212009.jpg

20150322_212020.jpg

Next steps are to clean it up a bit more, pull the valves and clean them, put it back together and see how it works.

A couple questions:
- The head gasket appears to be in good shape, should I get a new one or could it be re-used?
- The area around the engine block is filled with some sort of insulation-type material. You can see it at the top of the first picture. What is this and is it supposed to be there?