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12hp Tecumseh XL wont start

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williemon

04-23-2003 18:30:14

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This is on a Murry riding mower. Last weekend, mower fired up. Battery is weak, although it is only about a year old. May be low on water or just dirty. Had to boost it with my portable, rechargeable battery jumper. Done that several times in the past 4 months. Was going to perform a long , overdue maintanance checkup in a few weeks. Had to replace start switch about 2 months ago. Been running fine with the exception of the weak battery. When I went to shut off the engine last weekend after I had finished, I dropped it to idle and it quit. I thought nothing of it since it has done that before from time to time. This weekend, the engine would turn over, but would not run. Not even a sputter or cough. Checked plug. Looked good. Grounded it to the cylinder and watched it fire. It looked good to. It was dry though, like it had no gas. Put it back in, ground down on the starter with it choked for a bit. Checked plug. Again it was dry. I had gas, and it was flowing into the float bowl. Pulled carb and feild cleaned it. Pulled main and idle jet, wiped them and installed them. I think I went 1.5 out on main and 2.5 on idle. Installed freash gas. Now I still get spark, plug now gets wet, but it still wont make so much as a cough. Pulled flywheel. Cleaned mag posts and flywheel magnet. No points. Has EI. Key looked like a steel key and looked good as best I could tell. I did not figure a steel key would affect timeing. Ive tried choking it to death, and cranking with it in fast, but not choked. Theres no spit, sputter or anything. Starter is saying some 4 letter words at me so I need to quit on grinding on it. So the way I see it, I have air, gas, and spark. What am I missing?? I also tried my compression guage on it. I hooked it up and cranked away. I saw about 25 to 30 psi. Valve cover has 2 screws, so I pulled it off and the valves look to be working properly. I had a mm feeler guage and at TDC on compression stroke I measure a tight .5mm and on the lower a loose .5mm
What is all this supposed to measure? Thanks.

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Tim

10-29-2003 14:38:02

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Re: 12hp Tecumseh XL wont start in reply to williemon, 04-23-2003 18:30:14

What did you find out? I have the same engine and it is acting exactly the same as yours.

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r_d97

04-24-2003 08:57:43

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Re: 12hp Tecumseh XL wont start in reply to williemon, 04-23-2003 18:30:14

Hmmm, this is an interesting one. You do have plenty of valve lash, but if that is the correct compression results, it will never run. First, let try the easy stuff- you have done a good job troubleshooting but try changing the plug to a known good one. If that doesn't work, you might have a bad valve seat or burnt valve and need to pull the head to check. Post back what you find.

Edward

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Ben in KY

04-24-2003 08:42:19

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Re: 12hp Tecumseh XL wont start in reply to williemon, 04-23-2003 18:30:14

compressions seems a bit low to me, but not sure if that engine has compression release. My manuals are loaded out right now, so I can't check. Also you might want to check the spark timing with a timing light.
You seem to have covered most things very well.

good luck.

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williemon

04-27-2003 08:05:44

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Re: Re: 12hp Tecumseh XL wont start in reply to Ben in KY, 04-24-2003 08:42:19

Sorry it took a while to get back to you all. Thanks for the ideas. I thought about changing the sparkplug, but Id have to go get one. No big deal, but I felt that since I was seeing a good consistant spark in the plug gap with it out of the machine and grounded, it had to be fine, so I have focused elsewhere. I thought about the timing being off and checked the flywheel key, but it seems to be a steel key and everything there looks like it lines up properly. I also figured if it was slightly out of time, Id still get a spit, or cough from it from the carb or the muffler, but I get zilch. I have since pulled the valves and head. I cleaned all up very well. Valve seats look good and well pressed in, valves both looked good. The intake was carboned up a bit so I cleaned it up real well and cleaned the exhaust too. I saw signs of slight leakage between the head/cylinder/gasket at the bottom and starter side of the engine. The top and pushrod side was clean. I cleaned all that up as well as the piston. There was some very slight scoring of the cylinder in 1 or 2 places. You could feel it with the fingertip, but could not catch your fingernail on it. I replaced everything and tested again. Still only 30 psi. I noticed that the exhaust valve does a funny thing. As piston is on its compression stroke right after taking in a charge, the exhaust valve will crack open just a tiny amount, and when piston gets to about halfway in this stroke, the exhaust valve is closed again. What gives? Is this the effects of a compression reducer? Model # is OVXL120 202046D
Mower was manufactured in 10/90 Thanks all.

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williemon

03-09-2004 06:31:34

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Re: Re: Re: 12hp Tecumseh XL wont start in reply to williemon, 04-27-2003 08:05:44

This is a followup. Sorry it has been so long though. Shortly after my last post, I decided to start from scratch. I pulled the carb, cleaned it, bought the proper sparkplug, set the valve gap, got a new starter from ebay(old one finally quit)and put it all back together with freash gas and fired it up. Now it sings!!!

I found out that the sparkplug I had been useing was a short reach plug. I was supposed to have a long reach. So that may have been the main problem all along. Thanks all.

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Ned

05-04-2003 22:23:39

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Re: Re: Re: 12hp Tecumseh XL wont start in reply to williemon, 04-27-2003 08:05:44

That's the compression release. first thing I'd do is get new, or a known good spark plug, blow out the cyl. with compessed air, install plug, do not choke carb at first,If nothing, then choke to start. the only way you can get a correct compression reading is to spin engine backwards.
(Because of the release) The low reading is due to the release. If you spin backwards by hand, if it rebounds, that's enough to start it.
Checking Ign. by grounding to the head does'nt mean it will fire in chamber. Check the Flywheel/coil air gap. the easist way is with a calling card. Did you lap the valves before installing them? that would have helped, but it still should start, or backfire if you did not.
did you check the Ign. kill wire from the coil? is it grounding the coil? Isolate it, then you will know.
I hope this helps, good luck, Ned

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