149 runs...then gets bogged down
 

Hello,
So, the latest issue is that the engine will run fine for about 5 minutes or so then act like it is getting bogged down..that's the best way I can describe it. Loss of power, lots of vibration, struggles to stay running then dies. The last three times this has happened (last three times I've run the engine) it has ended with a backfire. There's also what looks like smoke or exhaust coming from near where the exhaust outlet is on the engine block. What's going on and how do I fix it? Thanks in advance, I truly appreciate it. Matthew+

Sounds like the coil is heating up and breaking down the spark. New coil time more than likely. I'll list a link to our library that will help you try and trouble shoot the coil with a multi meter.

http://www.onlycubcadets.net/forum/showthread.php?t=11

Also possible you may have a valve starting to stick open as it heats up. Usually is the exhaust.

I've had two Kohlers act up this way. One of them, the ignition points lost spring tension. The other, an exhaust valve would stick open.

In both cases the engines would start and run fine when cold but when they'd get hot, under a load, the symptoms would start. Both of them would start right back up after they cooled.

I agree with both the above suggestions. I have also seen restricted fuel filters cause similar results. After you let it sit a while, enough fuel will trickle into the carb bowl to allow it to run, but not for long. When I worked at a small engine dealership, it wasn't uncommon for an engine to run 20 - 30 minutes before coughing and sputtering when this happened. The filter would flow fuel, just not quite enough fuel to run the engine at full load. A $5 filter and 3 minutes would take care of the problem. On a 149, usually there is no external fuel filter. The filter is a screen on the inlet of the fuel valve inside the tank. You have to unscrew the valve from the tank to access it and clean it off. It won't cost anything to check.

Thanks, guys. I'm dreading that it is the coil. I just installed a new fuel shut off valve about a month ago and recently took the fuel tank off for some repainting...drained out all of the gas and looked around inside of it to see if there was any rust or other debris, and there was none, so I don't think it is the fuel filter. If the exhaust valve is getting stuck open, how do I fix/repair that? I'm sure that once I get it running properly again I'll have to fix the hydro unit or something else. HA. At least I've learned SO much on this rebuild, and thanks again to everyone on here...such a great amount of knowledge!

Thanks, Mike...Yeah, after mine tends to do the same thing, however, once the engine cools it will only run for 2-3 minutes instead of 5-6 minutes before getting bogged down.

If it IS the exhaust valve getting stuck open, how do I fix that? Thanks in advance, and again...Matthew+

Rev. Matthew, My 149 had the sticking valve problem a few years ago. It took me a while to be sure that was the problem. When it backfired and quit I stood beside the engine while it was cooling down. When it cooled down enough you could hear the exhaust valve snap shut, then it would start right up. I took the air cleaner off and squirted MMO in the carb with the engine at about 3/4 throttle. I gave it enough to almost choke it down, let it clear up and do it again. When I finished that I topped off the tank with fresh gas and plenty of MMO. I still run with more than the recommended amount of MMO and haven't had a problem since. I don't worry if it smokes a little on start up it clears almost immediately. I bought the tractor new in Jul. 73, the engine has not been apart and doesn't use oil between changes.

dclinansmith: Thanks, I'll try that and see if it helps. I haven't heard the exhaust valve snap shut as you mention above...although I don't think I was listening for that noise last time it happened. I used to have a bottle or two of MMO around somewhere in the garage.... I'll let you all know if that helps when I work on it tomorrow.

Compression gauge would tell you pretty quick it it's a valve problem.
Do a compression check cold and see what it is. Then run it till it quits, pull the plug and check it again. If it's low, pull the head and valve, clean and re-install. If it's the same, then it's on to the next test.

I would try the MMO using it in the crankcase for awhile too. Use fresh detergent oil in the engine.

I can't prove it but I believe using old, stale gasoline will make the valves get gummy and stick.

I have heard that valve snap shut as described above a time or two. But also when the engine would quit and try to restart, the engine would spin faster on crank speed and you could hear the compression puffing out the exhaust. Not much need to do a compression check with those symptoms.

So I got the whole day yesterday to tinker with the 149. I put a healthy dose of MMO in the gas tank and filled it with fresh gas. It ran just fine--puffed out some smoke at the beginning but that cleared up pretty quickly once it started. Ran it for about 10 minutes (until my hand got tired of holding the key in the start position--see other post about THAT issue) and everything seemed fine. But I DID get a backfire when I shut it off which surprised me because it seemed to be running just fine until then. Any idea why that's happening, and will it continue? Thanks again for the great ideas and suggestions. I'm determined to get this thing up and running!

A backfire on shut down is not totally uncommon. That happens because once the spark goes away to shut down the engine, raw fuel and oxygen enter the exhaust. If something is hot enough in the exhaust to ignite the mixture, bang, you have a backfire. At this point, I wouldn't be too concerned about a backfire. See how it does once you get it up and running for real.

Now you probably burned up the starter solenoid. You have to stop and fix the problems in order. You can't hold the key on while it's running. Fix that first. Or at least run a jumper. Or your just going to have more problems to fix.

If MMO made it run, then you probably have a sticky valve. MMO won't fix it. Pull the valves as I suggested. A backfire out exhaust could be too rich a fuel setting or too high an idle setting also. Along with about 5 other things, one of which is...... a sticky exhaust valve. Please fix the starting issue, and pull the valves. Then report back.

Thanks, Jonathan...I'll see what's what. Took the weekend off and was out of town, will report back once I get some time this week to get more done.

My 149 has backfired at shutdown for over 20 years (every single time like clockwork)... The solution that I use is to let it idle for about 30 seconds before I turn it off to let some of the richer exhaust leave the muffler... no more backfire.