Kohler with no power

[Jim Meade / Iowa City]

I have a 30 hp Kohler gas engine on my ZTM.  It's been running fine.  Today, I started it up and it doesn't have any guts.  I don't think it gets up to normal speed and it sure doesn't act like the governor kicks in.

Choke set right, throttle cable seems to extend correclty.  Runs smooth (just not strong).

Any ideas where to start? 

[Nebrfarmr]

Fuel filter, broken governer spring, partially sheared flywheel key, gunk in carb, bad spark, are all possibilities.

Probably the easiest to check is the fuel filter.

The flywheel key is what sets the timing on most smaller engines.  If the key partially shears, it retards the spark.  It will start fine, run fine, but not want to 'rev out' well.

A bad spark is pretty rare now-days with electronic ignition.  They usually have decent spark or not.

A broken spring in the governor will not allow it to rev out, as it will think the engine is running faster than it really is, and throttle down the carb.

[nwobcw]

   Does it rev up OK without the mowing deck engaged?   All of the other person's suggestions plus bad gas and a plugged air filter and bad spark plugs.

[Pupdaddy]

...My 25 horse Kohler has a fuel pump (I think it's run with vacuum somehow) I'd look for the fuel line coming from the carb to the pump (should be the first thing the line runs into) and try to gravity feed the engine to see if it winds up fully. There also may be something over the outlet in the fuel tank...blow back through the hose and see. I can't see it not getting enough air while not mowing to fully accelerate..but it's a possibility. Funniest thing I've had happen lately to mine...was I ran it out of gas the other week. Doesn't sound too bad...until I restarted it..and it would only run on one cylinder. Messed around with it..had spark on both sides...switched plugs..still wouldn't fire. I started investigating other things..and pulled the valve cover. Low and behold the exhaust pushrod was bent and off the seat. I straightened it..put it back in...(just to see if it would stay) and it jumped off again. I could feel something funny when I pushed the exhaust valve down..like it was bent too...and I ended up pulling the head. Low and behold..when I ran it out of gas...either the motor was so hot....the exhaust seat loosened up in the aluminum head...and dropped, or the valve somehow stuck to the seat..and pulled it out of the head. Needless to say..the head was junk..valve was junk..pushrod was junk...and my friendly parts dealer was more than happy to sell me $216 worth of parts to fix it....all because I was too lazy to check the gas..LOL

[nwobcw]

   Pup it sounds like that engine is running awful lean which makes it run hot for all that to happen.

[Jim Meade / Iowa City]

You have to specify what you mean by awful lean.  Most engines run rich of peak exhaust gas temperature (EGT).  That is, there is more gas in the mixture than needed and the extra gas cools the engine.  Of course, it's wasted. 

As you lean the engine out and get it closer and closer to peak EGT, it will run with more and more power but will run hotter.  It has the most power at about 25° rich of peak and is most economical at peak.  But, it's way too hot.

If you go on and lean the engine so there is less gas than air in the mixture (lean of peak) the engine will start running cooler again.  Most carbureted engines don't have even enough fuel distribution to run LOP smoothly.  Injected engines can if the injectors are balanced, which most are not.  It's cooler because there is less gas being burned.

LOP is just as cool and much more economical.  It also produces less horsepower.  It's very difficult to harm an engine LOP.  Timing and the ignition system have to be in very good condition.  When running LOP, cylinder head temps go down and EGT stays pretty high.  Valves are cleaner because you don't have excess fuel in there to coat things.

I don't know of anything except some aircraft engines are are normally flown LOP.  There is a very big controversy in the aviation industry as to whether LOP or ROP is the way to go, but more and more people are seeing the benefit of LOP.  When I ran ROP I could go for about 4.5 hours and when I flew LOP I could make 6.5 hours.  Of course, I was aboutt 10 knots (15 mph) slower at LOP, but made up in range by skipping time-consuming fuel stops.   

I know this doesn't have much to do with farming, but though some of you might be interested to know of a situation where you deliberately run an engine leaned out that far.   Some of the big radial aircraft engines ran LOP all the time and some new engines have it in the manual to run LOP.

[Jim Meade / Iowa City]

I'll take a look at those things.  I did check the air cleaner and it looked OK.  The engine does not seem to rev up enough when not under load.  Runs smooth but a little slow or at least a little gutless.  I did just fill it with gas, but everything else is getting along OK on the gas.  However, I'll look into that.

Thanks for all the tips.  I'm no engine man.

[Pupdaddy]

With the new air pollution requirements...the manufacturers are designing these motors to run very lean...probably too lean in my opinion for long life. You can't adjust the high speed needle valve in these carburetors any more..they either cover them with plugs..or install them so they're not adjustable. In the meantime..we still let varnish and gunk accumulate over the winter in these motors...and that will eventually lead to a plugged needle valve..and an engine too lean to run. I doubt that's your problem with yours..although we have had small pieces of dirt get stuck in the carburetor...and you just have to disassemble it..and run a tag wire carefully through every hole. The symptoms usually aren't lack of rpm's...but a loping idle that will barely keep running. Good luck on finding the problem...I find myself wishing I could just hire the lawn mowed sometimes...LOL

[nwobcw]

  Awful lean means leaner than it should be.  I don't know any other way to put it.   Most of these small engine carbs aren't adjustable any more though.   I have heard of 2 cycle engines suffering engine damage by running out of fuel but never a 4 cycle engine.

[nwobcw]

   Also spray some ether or brake cleaner around the head gasket.  Maybe it blew and the engine is sucking air through the blown head gasket.   But that might cause a miss too.