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I'm guessing it's the coil.

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I'm guessing it's the coil.

Postby 38racing » Tue Jun 25, 2019 9:56 pm

Lv148 tecumseh on a dumpster mtd unit. Like usual I check for oil and blade and controls and then spray some carb cleaner and see if it starts. This one did but i sensed some vibration. I found the blade turned 90 degrees to the adapter. Turns out the adapter bowtie was damaged. So after a new adapter and blade I get no fire. I put the inline spark tester and thought I had a spark. I decided to pull valve cover and valves are moving ok. I pulled the starter and flywheel key looked ever so slightly shifted. I pulled the flywheel and there was no shearing. I raised key to flywheel edge and aligned it and torqued to spec. Still no fire. Decided to check spark again as it was now dark. No spark with inline tester between coil wire and plug. If I ground the inline I get spark. Tried with 2 different plugs. One from a mower that had just run. I will try a new one tomorrow just to be sure but it's looking like coil died right after my first test start.
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Re: I'm guessing it's the coil.

Postby bgsengine » Wed Jun 26, 2019 6:20 am

try a different tester , too.. inline tester + spark plug under compression may just be too much for those coils.. check your compression also, try with coil ground lead unhooked from coil, It'd be pretty unusual for that sequence of events - could be you disturbed something (ground wire routing, high tension lead need closer inspection- might be shorting somewhere, etc... any rust on armature mounting surfaces? (rust between coil and block can cause ground path issues) )
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Re: I'm guessing it's the coil.

Postby KE4AVB » Wed Jun 26, 2019 8:08 am

Also can be a rusted terminal on the HV lead or an internal lead break. I have seen several over the years that I have replaced on various coils.
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Re: I'm guessing it's the coil.

Postby Skywatcher » Wed Jun 26, 2019 10:09 am

Hi 38

On these CDI ignition engines, flywheel position has no effect on whether the coil fires or not, the flywheel key just makes sure the spark hits at the right time. The most common reason why these engines lose their spark is a seizing or seized engine control cable not fully opening the ignition grounding switch. As BG says, disconnect the small green wire from the coil to isolate the ignition system from the rest of the machine.

The spark tester I use is the Stens 750-018 https://www.stens.com/search?keywords=750018 which works on the KISS system. Remove the sparkplug from the engine, connect the tester to the plug wire, clip it to a cooling fin and spin the engine. If the ignition system can jump the 3/8" gap at atmospheric pressure, it can jump the 0.030" gap under engine compression. Hope this helps,

Sky
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Re: I'm guessing it's the coil.

Postby 38racing » Wed Jun 26, 2019 11:01 am

Skywatcher wrote:Hi 38

On these CDI ignition engines, flywheel position has no effect on whether the coil fires or not, the flywheel key just makes sure the spark hits at the right time. The most common reason why these engines lose their spark is a seizing or seized engine control cable not fully opening the ignition grounding switch. As BG says, disconnect the small green wire from the coil to isolate the ignition system from the rest of the machine.

The spark tester I use is the Stens 750-018 https://www.stens.com/search?keywords=750018 which works on the KISS system. Remove the sparkplug from the engine, connect the tester to the plug wire, clip it to a cooling fin and spin the engine. If the ignition system can jump the 3/8" gap at atmospheric pressure, it can jump the 0.030" gap under engine compression. Hope this helps,

Sky

I have that tester too. Always see to have trouble getting it to stay clipped. Will try it. I pulled the the flywheel because I thought I saw a spark and with no fire thought it might be the timing. I'll retry with new plug and kill wire off . I didn't bother with taking it off last night since it sparks the grounded tester. I have a few tecumseh mowers sitting around so I should have a matching coil to try as well.
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Re: I'm guessing it's the coil.

Postby 38racing » Wed Jun 26, 2019 9:26 pm

And I guessed wrong and you guys were right. Tried 3 coils and results seemed same although wife saw spark on number 2. Number 3 came off a mower that had run earlier tonight and I saw spark on the problem mower and the donor mowerand is now running with my original suspect coil. I checked compression and was shy of 50. Checked valve movement and clearance. Seemed ok. Pulled the head and valves looked ok but some serious scoring on the cylinder. I just wish the darn thing had never fired up on my first test. Another unit arrived at the dumpster yesterday. Second one with wheel adjuster ripping section of deck out. Not sure how people do that unless they are running over them with vehicles.
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