Yard Machine MTD mower

[lefty]

Model:1A-B9BG729
26-047
Serial: 1D094KA1454

This one is puzzling me. Sorry for not having the engine numbers right now and I can get them if they will help but thought I'd post in the meantime.

This came in as running for a few minutes, stalling and then not starting again. I suspected anything from a gas cap vent to auto choke. It's one of the ones with the spring and plastic arm that goes over to the lever on the exhaust. All that looks operational. When I got it, it would just cough for a second and not start. So I cleaned the carb and it fired right up. Ran it for about 10-15 and it appears to run perfectly. The puzzling part is that my tach is showing it fluctuating between 1900 and 3100 rpm. I can't pick it up with my ear but that's what it says. I tried a new battery on my tach and tested it on a known good machine and it appears to work fine and steady. So this machine, although I can't hear it, is fluctuating between 1900 and 3100 rpm. Bounces from 1900, 2500, 3100, 2700, etc. I'm shocked that I can't hear that. Is this possibly the sign of a coil on its way out? If I didn't put my tach on this, I would have just sent it on its way. It's really not audible, to me anyway.

Thanks

[bgsengine]

Doesnt mean it's changing RPM - I presume you are using an inductive electronic tach - it depends on counting the ignition pulses it detects in the plug wire, could be you are seeing an ignition drop-out (weak spark) - Have you checked the spark plug to be sure it is correct? Electromagnetic interference with the tachometer's pickup can cause a mis-count in the meter. I encounter them every so often more often on some chainsaws , but see it on 4-strokes too... It isn't really mis-firing (verfiied that with a spark tester) but the tachometer's pickup just isn't detecting the ignition pulse.. Sometimes changing out the plug to a resistor type made a difference, sometimes not - It doesnt happen very often in my experience, but have seen it every once in a while.. I have a very reliable Treysit Sirometer (Vibration Tach) and also used to have a diesel tach (photoelectric) and was always able to verify correct RPM with one or the other despite the tachometer not reading correctly (But I havent seen that happen since I been using the OEM Echo Oppama tach)

[lefty]

Thank you.

[creia]

[quote="bgsengine"] I have a very reliable Treysit Sirometer (Vibration Tach)
I bought one about 10 years ago- One of the best, most dependable, and useful purchases I have ever made.
Michael

[lefty]

I just looked up one of those tachs. Fascinating. I'll have to pick one up.

[lefty]

I just realized I gave you the wrong model number. I don't think it matters for my question but it brings up another. It looks like when they printed this model sticker at the factory, it cut off the first bit of it. Any suggestions on how to reverse engineer the first number in the model? I attached a link to a pic of the tag.

https://photos.app.goo.gl/2HepL2bm4LwgL8od9

Thank you

[bgsengine]

I just realized I gave you the wrong model number. I don't think it matters for my question but it brings up another. It looks like when they printed this model sticker at the factory, it cut off the first bit of it. Any suggestions on how to reverse engineer the first number in the model? I attached a link to a pic of the tag.

https://photos.app.goo.gl/2HepL2bm4LwgL8od9

Thank you

Depends on what equipment is - 11A - Pushmower,,,, 12A - Self Propelled pushmower,,,, 13A - Lawn/Yard tractor... 14A - Garden Tractor... 17A = Zero Turn... 24A - Chore machines (Edgers, chippers, etc) 31A - Snowblower and those are just examples - read up on MTD model numbering system.

[dougand3]

Since it's ?1A, I'd say 11A- push mower. But the engine # is more important here. On valve cover, shroud near muffler or dot stamped into block.

[lefty]

Looks like it's going to be a regular push mower, non-self-propelled, 11A. I'm done with it but wanted to be sure about that one so I could pull up the owner's manual for the machine. Thank you.