I have a Yard Man/MTD model 11B-106C401 with your usual side valve engine. Here is the break down for the engine.

The engine starts easy and runs like a champ but occasionally dies when mowing. It seemed temperature related so I've replaced the coil but the problem has not changed. It mows 15 minutes and then dies and will not even try to fire until it's cooled for 10-15 minutes then will run for 5 minutes and dies and will not start unless it's cooled for 10 or 15. When it dies it sputters for a few seconds and then quits and will not try to fire until it's cooled. I'll pop out at lunch and grab another spark plug to try but I'm not confident that will help.

Right now I've had the engine running no load for half and hour (it's still running) and it still has not died. I've shaken and jostled the mower and it's still runs smooth but I assume it's not getting hot enough without a load. Dare I invest in another coil for this 10+ year old cheapie mower? Am I missing something?

 

If it dies like shutting off a switch it could be ignition related, check for spark as soon as it dies, if it sputters to a stop like it is running out of gas, try removing/loosening the fuel cap when it starts to die. Have a good one. Geo

 

Sounds like the fuel tank isn't venting properly. A vacuum get created in the tank and eventually starves the engine for fuel. Loosen the cap and see if that solves the problem. Might also check to see if there is crud in the bottom of the tank blocking fuel flow.

 

Thanks for the tips. I'll try it next time with the cap loosened a bit.

I've removed & cleaned the fuel tank and removed & cleaned the carb. I have not tried loosening the gas cap since it runs forever when it's just sitting there. I've only been able to get it to die while mowing. But running at full throttle without a load may not consume fast enough to make a vent problem appear.

 

The problem continues.

I have tried loosening the gas cap and it has no affect on the problem so I don't think it's a vent problem.

Today when the mower was good and hot and running well I killed the engine (on purpose) and tried to restart it. It was dead and did not even attempt to fire. I let it cool for half an hour and it fired right up on the first pull and ran perfectly.

I'm still thinking it's the coil but I've got two coils. The original and a brand new one and the problem occurs with both. What am I missing?

 

Do you have any spark when it quits as geogrubb asked?? If so, the coil is fine...As a Long shot, It may even be a valve adjust.. Post the result of the spark test & the pros will get you dialed in with this....

Roger

 

Pilot you didn't mention if you have performed maintenance around air filter and spark plug, as well as confirmed that the plug gap is set correctly. It could be as simple as a moody spark plug. I assume you are using fresh gas, and if not have a stabilizer in it. Did you give it a compression test to confirm that the valves and rings are doing their thing also. If not and you have confirmed about the plug, I think you are ready for that check now as you already have looked at carb and coil failures. Valves could be all carboned up, or even one could be cracked. Like you, I am just trying to think about what have you missed.

 

When it's hot & dead I am not getting a spark, but I removed the plug and held it against the case so it is possibly a bad plug. I should put another plug in it and the next time it quits I'll check to see if there is spark at the end of the plug wire.

The gas is fresh and it runs well for 10+ minutes and after it's cooled down it runs well again so I don't suspect the fuel or carb. I have not done a compression test or pulled the head to look at the valves.

 

I'd start looking at wire connections on your keyswitch, positive battery cable at BOTH ends, negative battery cable at BOTH ends, at the starter itself and the starter solenoid. I feel it's unlikely that you have 2 bad coils (although it has happened before). I'm thinking somewhere a bad or loose connection is getting hot and cutting everything off.

 

This is an el-cheapo push mower. No self propelled, no electric start, no battery. There is really nothing more than the coil, spark plug wire, spark plug and the kill switch at the flywheel/blade brake. There is not much to go wrong.

 

Try un plugging the kill wire from the coil, maybe the clutch brake cable has stretched or something, you will need to pull the plug wire to shut it off after pulling the wire. If it still dies it has to be the coil or the coil is loosing ground, try sanding the mating surfaces of the frame and coil. Have a good one. Geo

 

Pilot just asking that when you said you replaced the coil, were you referring to some kind of ignition module? No breaker points in there under the flywheel also right?

 

Can you spot what's wrong in this picture?

Yes, I have thrown in the towel. I broke down and bought a new Husqvarna since I could not find the problem with my old engine. I was so impressed with the quality of the new Husqvarna mower that I pulled the motor off and put it on my old Yard Man chassis. The old engine is now on the bench. I'm dying to find the cause of the problem. Now that I have a running mower again I have the time to take the old engine down looking for a cause.

PS: No, I did not bother mounting my old motor on the Husqvarna chassis. It's just sitting there for the photo.

 

Ummm..PD...I have to ask....why the heck would you pull a motor off a brand new mower and put it on an old chassis?

If you were going to do that...why not just buy a bare engine?

Seems like buying a new Corvette to take the engine out and put it in a '67 Stingray....lol. At least to me.

 

Maybe it's the heat, economy, stars, planet alignment or whatever but I don't understand destroying a new mower to fix and old mower. Have a good one. Geo

 

Oh, believe me. The humor, or lack of intelligence is not lost on me. I am glad there was nobody around because I was cursing like a sailor as I swapped engines wondering what just a motor would have cost.

I post enough on here I might as well show the not so proud moments.

I will feel even more stupid if I end up finding a simple little problem in the old engine that I overlooked.

 

Try Small Engine Warehouse - Repower Outdoor Power Equipment for a replacement engine, it would probably have been cheaper. Have a good one. Geo

 

Thanks for the link but I really wish I had not seen their prices. Buying a replacement engine would have been much less expensive.