# Lawnflite MTD "walk behind" mower dies when warm



## gregr (Jul 11, 2008)

I have had this mower for over 15 years with minimal maintenance, i.e., hardly any ... 

Unfortunately, there is no model or serial number that I can provide ... I never noticed that until yesterday when I wanted to record the information. All I can see on the equipment is that it's an MTD "Lawnflite" with a Briggs & Stratton "Classic" engine. I don't know its horsepower unless someone knows where I can find that info. I was able to locate the owner's manual, but it refers me to a separate engine manual which I can't find. (If you need me to take pictures of the mower and engine, let me know and I'll post them here.)

In a nutshell, the problem started after I had finished cutting my backyard and was ready to begin on the front lawn, but couldn't get it to start. Prior to that, I had to routinely stop the mower to empty the side bag while working on the backyard and never had any issues firing it back up.

It wasn't raining that day; in fact, it was ideal mowing conditions. There was enough gas, but I topped it up to be sure. I tried pulling the cord at least 20 times, but there was never any sound of the engine attempting to turn over. I didn't detect any smell of gas like it had flooded the engine (if that happens with mowers ... I don't really know; I'm a PC repair expert but a noob when it comes to small engine repair!).

I ended up leaving the mower in storage for a week and then worked on it a few days ago. I disassembled the carburetor and air filter, fuel tank (which I emptied), and removed the panel which covers the "explosion chamber" which exposed the carbon-encrusted piston and 2 valves. I cleaned the carbon off the piston and valve heads and examined the carburetor for any obvious problems (didn't see any). I drained the oil (came out like thick molasses ... how embarrassing!) and replaced it with a fresh change of 2-cycle engine oil.

I also cleaned the CJ8 spark plug with sand paper, reset the spark gap (.025), re-assembled the engine, cleaned the air filter and saturated it with clean oil, refilled the tank with fresh fuel and gave a quick pull on the cord. The engine started immediately and I also noticed that pulling the cord was alot easier (I guess a fresh oil change will do that ...!). The engine responded quite nicely and ran for about 5 minutes. I then stopped it and tried again ... it wouldn't start!! I pulled the cord about 10 times but it wouldn't show any signs of turning over. In fact, it seemed like the same symptoms I experienced the very first time I was having problems.

Thinking that the spark plug might be too old, I decided to buy a new one the following day. When I brought the new plug home, I was curious to see if I could start the engine before replacing the plug. Well, it did ... on the first pull. I assumed that perhaps the old plug might have lost its ability to spark after a few minutes of use, so I changed it with the new one.

After replacing the plug, I fired up the engine with no problem and assumed the problem was solved. I began cutting my backyard lawn since it hadn't been done for a few weeks and only to go for about 10 minutes when the engine sputtered and died ... AGAIN.

I tried starting it again, but after 5 pulls I realized that the problem was never resolved because once more the engine showed no signs of turning over.

At this point, I concluded that the engine has no problem with cold starts. It only begins to happen when the engine gets hot.

Would anyone know if this is a common problem and if it can be fixed fairly easily?

Thanks in advance!!

Greg


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## dawgpile (Apr 28, 2008)

Greg. FYI, I'm pretty confident you have a 4 cycle engine, not a 2 cycle. You did the right thing by "de-carbeurizing" the head when you took it apart. You need to change the oil to a straight SAE 30, instead of the 2 cycle oil. You can use 10W-30 but straight 30 weight is better.

It would be very helpful if you posted the engine numbers. You can locate them on the engine itself, typically stamped somewhere on the 'shroud' which is basically the metal cover over the starter cord assembly or if it's plastic, they can be on a metal plate. In general they are typically on the spark plug side of the engine. Take a close look around the engine and you should find a couple sets of numbers. They consist of the "model" "type" and "code". Go here: http://www.briggsandstratton.com/maint_repair/manual_and_more/
and dowload the numbering system fact sheet and this will make more sense.

With those numbers you can obtain the engine manual and the parts list right from the B&S website.

Also, unless your owner's manual spec'd it, I don't think it would normally take a CJ8 plug or have a 0.025 gap. Normally B&S engines of this type are gapped at 0.030. This is a minor issue and I don't believe contributing to your underlying problem.

See if you can find the numbers and post them. We'll provide some additional help from there.

You may have one of the engines with a thermostatically controlled(spring) automatic choke which when cold, holds it closed and when warm should keep it open. If that is not working properly, you may be trying to start a warm engine under full choke condition which is difficult if not impossible.

Let us know...


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## phillipmc (Jan 27, 2008)

That must of been an expensive oil change.


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## gregr (Jul 11, 2008)

dawgpile said:


> ... It would be very helpful if you posted the engine numbers ... With those numbers you can obtain the engine manual and the parts list right from the B&S website ...


That's great advice. I will do it tomorrow and post back then.



> ... You may have one of the engines with a thermostatically controlled(spring) automatic choke which when cold, holds it closed and when warm should keep it open. If that is not working properly, you may be trying to start a warm engine under full choke condition which is difficult if not impossible ...


Hmm, I didn't consider that. Sounds like a good theory, _dawgpile_.



phillipmc said:


> That must of been an expensive oil change.


You're absolutely right, Phillip! :lol:


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## gregr (Jul 11, 2008)

OK, the engine information requested is as follows:

MODEL: 92502
TYPE: 3194 01
CODE: 90043004

The following link is for the B&S Manuals, Parts List & Wiring Diagrams:

http://tinyurl.com/6ok4o4

but I don't know which PDF file to use since it has several documents which cover type 3194 for model 92502, so I don't know what my next step should be.


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## gregr (Jul 11, 2008)

gregr said:


> ... The following link is for the B&S Manuals, Parts List & Wiring Diagrams:
> 
> http://tinyurl.com/6ok4o4
> 
> but I don't know which PDF file to use since it has several documents which cover type 3194 for model 92502, so I don't know what my next step should be.


No worries ... I found the original paper manual when I was just cleaning out the shed. I need to review it to see what I can find regarding the choke info.


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## dawgpile (Apr 28, 2008)

Greg, this engine has an automatic choke but does not control it thermostatically. In other words, it is not affected by temp which can make these engines notoriously difficult to start when warm. The best way to start it when warm is to put the throttle on its lowest setting(idle) since the choke will be closed.

FYI, if you look at any of the IPL's for your engine, look at the carb diaphragm (part no. 394). Integral to that diaphragm is a link with a spring assy below the diaphragm which sits in a well in the top of the fuel tank. That diaphragm is subject to engine vacuum which pulls on the link and opens the choke when the engine is running, proportional to speed meaning it opens the most at wide open throttle(highest vacuum).

It might be wise to go ahead and replace the diaphragm as it's inexpensive(<$10). Then you know it's ok. If you choose to do this, when you pull the tank away from the carb, that well the choke spring sits in should be absolutely dry. No gas in it. If there is that means you may have other problems related to how flat or 'true' the top of the tank is w.r.t. the bottom of the carb. Let's not go there just yet. When you re-attach the carb to the tank, snug up the 5 screws evenly.

Again, I'd make sure you change the oil to the proper amount of SAE 30, make sure you have the correct plug gapped to the proper dimension(0.030) and then try the technique of starting the warm engine on the lowest throttle position. Beyond this, some potential mixture 'tweaks' via adjustment to the needle valve may improve the situation.


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## dawgpile (Apr 28, 2008)

Greg, I wanted to add the following after re-reading your post. Initially I was thinking this was just a hot restart problem. But, you said the engine quit on its own after a few minutes of operation. A common cause of the symptom you describe is when the vent in the gas tank cap gets plugged. Fuel cannot be drawn up the pickup tube after a period of running time. This is simple to test for. Try loosening the cap when the problem happens again and see if that aids in re-starting.

The hard hot starting nature of these Automatic Chokes would not contribute to the engine stopping on its own, only a potential source of difficulty on re-starting. It is particularly apparent on mowers with 'high intertia' type blades. When the engine is shut off to empty the bag for example, the engine keeps turning a lot and basically floods the engine causing it to start with difficulty. I owned one of these with a high intertia blade. The blade was a large round disc with 4 small blades attached. It was tuff to pull initially because of the intertia. This mower was difficult to restart hot and required leaning out the carb to fix the problem. Again, if you haven't changed the diaphragm in many years, I'd still consider doing that as a good preventative maintenance measure.

Try loosening the tank cap! Keep us posted!


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## gregr (Jul 11, 2008)

_dawgpile_, sorry for letting your posts go unanswered.

I have been busy with other obligations and haven't even had a chance to address the mower until today. As it happened, my neighbor has taken pity on me and lent me her mower for the last few weeks until I got around to fixing my own.

Anyhow, I am looking around for a replacement diaphragm and may be able to pick one up in the next few minutes. If I can get that done, I will give it a go. If that doesn't work, I will then try your gas tank cap idea.

Thanx for your suggestions thus far ...! 

- Greg


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## pyro_maniac69 (Aug 12, 2007)

Get the 2-stroke oil out of there ASAP, that WILL damage the internals of the motor after so much use


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## gregr (Jul 11, 2008)

pyro_maniac69 said:


> Get the 2-stroke oil out of there ASAP, that WILL damage the internals of the motor after so much use


Done! Replaced with SAE 30 ... 

_*dawgpile*_, I just wanted to let you know that the diaphragm was the problem. Thanx for pointing me in the right direction! Cheers!! :thumbsup:

(Admin, this thread can be marked "resolved" and closed if necessary.)


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## dawgpile (Apr 28, 2008)

Greg

Thanks for the follow-up letting us know what the problem turned out to be! Glad you got it going!

Enjoy....


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