cpete1 331 #1 Posted May 13, 2011 I have a strange situation with a twin cyl Kohler. Engine runs fine but then suddenly starts to misfire. One cylinder loses power but there is still significant heat and pressure coming out that side's exhaust. It may run like that for a minute but then suddenly regain power and run smooth. I've, to date, disassembled carb and cleaned. switched wires on the twin coil, (no change), switched spark plugs, (no change). Blown out the fuel lines, Re-timed the engine. There is no significant smoke like one would expect, black for unburnt gas or oil. The lastest idea I have is that the coil is getting weak but switching the spark plug wires doesn't change the side that is mis-firing. This one has me stumped. I haven't given up yet but its got me be-fuddled. Color of plugs looks good. It some times back-fires when starting. I might not have the timing perfect but when it runs ok which is 80% of the time, its running quite smooth. The issue tends to happen under a little load but nothing substancial. Anybody have a guess?? Glad the snow finally left.. Chris Share this post Link to post Share on other sites
buckrancher 2,668 #2 Posted May 13, 2011 off the top of my head it sounds like a sticky exhaust valve to me Brian Share this post Link to post Share on other sites
stevasaurus 22,229 #3 Posted May 13, 2011 Ditto on what Brian said... I had on outboard engine that did the same thing. Turned out to be the rings sticking...bottom cylinder was not getting enough of the oil/gas mixture. So much for auto blends. Anyway, they gave me some type of penetrating spray, and told me to spray it down the carb when it was warmed up and running...until the engine quit. Let it set for a little while (1/2 hour) and then start and run it. Do this every other time you have it running. It worked for me, and I would think it would work for you no matter if it was the valve or the rings. At least you will know if it is inside the engine. Share this post Link to post Share on other sites
cpete1 331 #4 Posted May 14, 2011 Thanks for the input guys. I haven't had a chance to look things over again but the suggestions make sense. A little extra load creates some additional heat which tightens up where ever the bind is. An exhaust valve would still allow combustion but less pressure. Its always the same side so I'm inclined to believe we're onto something here. Man this is a great site. Thank you again, I'll report back with what I find. Chris Share this post Link to post Share on other sites
cpete1 331 #5 Posted June 13, 2011 Well, I finally got into the engine and found a couple of issues. I took the head off the cyl in question and found grease and dirt had accumulated on the front edge of the fins of the head, which could in theory block the air from the cooling fan in the engine from passing thru the fins. I sprayed deep creep sea-foam around the exhaust valve stem, also checked the other side under the inspection plate. The valve seemed free enough and could turn easily. The last issue was the fuel filter. I think it was too small to begin with and had quite a bit of crap inside so I changed that out. Also set the timing back as I had little success with a timing lite trying to set it. The engine runs much better now and for the time being, the back-firing has stopped. I also de-carboned everything I could when the head was off. I think that was the main culprit. Extra heat would ignite the mixture. The problem mostly occurred under heavy usage so I think it was a heat "thing". Anyways, thank you guys (and gals) for the help from the site. Great bunch of people, glad to be a part of it. Chris Share this post Link to post Share on other sites
