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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #1 (Edited)
So I told a friend I would fix his grandmother's mower. What I didn't know is that it sat outside for a few years. There was lots of rust on the coil, and sanded it clean. I gave up on the carb and swapped in one from another Tecumseh. It does run different, but overall very unacceptable, and with some of the same misfire characteristics. The engine will surge badly, then find itself, and then it will sit there and run rough with a terrible misfire. After a few minutes of that, it will start surging again. The carb I put in I think is from a newer model than the one that was on the mower, it had a plug over the jet. I took the carb apart and sprayed it down with carb cleaner. I took the jet out and made sure it was clean. I have swapped the jets. I have changed the spark plug. There doesn't seem to be any oily residue around the head. I have even used a last-resort carbon removal method...water through the carb, hoping It would dis-lodge any piece of carbon. I don't know what else to do. Any suggestions are appreciated.

something told me not to take this job...I'm going back outside to mulch with my Lawn Boy.
 

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2 stroke enthusiast
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6,568 Posts
Outside of the carb swaps and cleaning methods, pull the head. You may have a sticking exhaust valve either due to carbon or rust.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #3
Outside of the carb swaps and cleaning methods, pull the head. You may have a sticking exhaust valve either due to carbon or rust.
Compression test...Thanks for the idea.
 

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443 Posts
Possibly a bad spark plug? I have had it happen before. I had a plug that would work when cold and as soon as the engine warmed up, it would just quit like it ran out of gas. Had another that ran like crap and backfired. They may look new, but occasionally a bad one gets out.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #5
Outside of the carb swaps and cleaning methods, pull the head. You may have a sticking exhaust valve either due to carbon or rust.
Compression tester broken....head coming off. I would have liked to listen for air escaping. Oh well.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #6
Possibly a bad spark plug? I have had it happen before. I had a plug that would work when cold and as soon as the engine warmed up, it would just quit like it ran out of gas. Had another that ran like crap and backfired. They may look new, but occasionally a bad one gets out.
Yeah, I've seen that too. I have tried it with a known good plug.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #8 (Edited)
I took the head off and found (of course) a lot of carbon. Some of this carbon seemed to interfere with the intake valve. I would have guessed the exhaust valve like echoman suggested because of the occational backfire through the exhaust. Anyway, can't get a head gasket until Saturday, so I guess I'll just have to wait. BUT this is a good thing...while it's apart I would still like any ideas on this. Thanks for the replies, gets my brain working again, it's been dormant for quite a while. :)

***edit***scipper, the fuel system seems to be ok. New fuel line, and there is no problem with fuel flow. Thanks for the suggestion, good thought.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #9 (Edited)
I took the head off, lapped the valves and did a good carbon cleaning. The surging is gone, for the most part. It fires up on the first pull, surges until it's warm (this is a major improvement), and has really good power. But there is still a misfire/backfire through the exhaust. I filmed it, but it is really hard to hear...my camera was unable to get good audio of the misfire, but in the last few seconds you can get an idea of it's rhythm. Also you can see the governor working a little. I don't know if this is normal operation. My friend needs his mower and I hate to give it back not running perfectly. thanks again.

http://www.youtube.com/watch?v=pzSoC2IzBKw

hang on...uploading a vid with better audio...

Ok...here it is. http://www.youtube.com/watch?v=m_yfKcRYCaA
 

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does it blow blue smoke when it back fires.could be pushing alittle oil pass the rings.that will wet the plug and make it hunt.tecs are great when running right.other wise.oboy.
 

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1,263 Posts
It's still quite rich. That air filter looks nasty- Have you tried running it minus the air filter, or with a new one?
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #12
There's no smoke. Actually you can still see the cross-hatch in the cylinder with surprisingly little 'normal' damage. 4X4...I just went out and tried it with and without the air filter, no difference. I checked the float level, and it was a little high so I bent it down a little and it didn't change much. Would a bad coil do this? It's solid state.

Thanks for the ideas.
 

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OMC & Ariens lover!
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1,296 Posts
yes a coil plug can and will do that...a V engine lawnboy showed me all about it lol
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #14
Ok...I'll see if I can scrounge one up to try. Thanks.
 

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576 Posts
-Do you still have the original carb? What was wrong with it? Also have you checked to see if the flywheel key is partially sheared? Could possibly be that the governor spring isn't hooked up properly or just worn out. You said that the coil was rusted. Did you notice if the plug wire insulation or coil insulation was cracked? Another simple check is to remove the gas cap while it's running. If it clears up, then it's just that the cap vent is plugged.

L8R,
Matt
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #16
I do still have the original carb, however is has been destroyed, by me. I put a new fuel inlet elbow on it and when I decided to replace the carb, I cut the new elbow out to put it in the 'new' carb. I have not checked the key...good advise. MR FIX IT says he has a coil I can try, so I'm gonna do that Sunday. It's nice because he lives only about a mile away. I think the gas cap vent is ok. I am gonna look at the key while it's apart...good idea. Thanks.
 

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Premium Member
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Sounds like it's running too lean. The idle circuit is clogged. Manually slow the engine down, if it wants to stall, that's your problem. Don't worry about cleaning the coil or compression. If it has enough compression to start, it has enough to run.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #18 (Edited)
Sounds like it's running too lean. The idle circuit is clogged. Manually slow the engine down, if it wants to stall, that's your problem. Don't worry about cleaning the coil or compression. If it has enough compression to start, it has enough to run.
I think you're right. I have changed the coil...very little difference in running. So, when I ran it I put my thumb over the air inlet and slowly started to "choke" the engine and it began to smooth out. I have some work to do, I already thought I had this thing cleaned out real good. At least I have something to go on. Thanks for the suggestion that it was lean. Update soon... These tecumsehs can really be difficult at times.

***edit*** I did push the gov to idle, and it still ran...like crap...but it ran.
 

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I had one that surged and mis fired but mowed great. I tried this, that and the other thing. Cleaned the carb about fifty times. This went on for a few YEARS. Know what it was? The AIR filter. The paper didn't look dirty but I guess the fibers were moisture damaged or something. I put a new filter on and it ran like a watch.
 

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OMG I got another LawnBoy
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1,178 Posts
Discussion Starter #20
I've tried it with and without an air filter. I am looking at the a/f mixture. For a quick test, I want to drill out the pilot jet. does anyone know the stock diameter so I can drill just a little larger for a test...I have about 3 of these jets laying around. thanks.
 
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