OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Tecumseh 13.5 hp

Paul, would you mind trying this again first, with your in-line spark tester?

This is a change in behaviour, since it no longer pays attention to the choke. From your comment about fuel coming over the top of the float bowl sounds as if it is now flooding, which again points to a float bowl problem. Bear in mind that a float bowl problem could have caused your previous lean mixture situation.

Hi Grumpy, have done previous test but with in-line spark tester and this is what i came up with.
Will only run properly with throttle held just above idling with nice constant spark. If i try to drop the revs or up the revs it will cough, splutters as you know, what i did notice was as soon as the motor started to play up so did the spark, it was almost is if it had a constant miss until i brought the throttle back to were it was running best. The spark was still there it just seem to loose some so of it punch so to say. Let me now if i have explained this properly Grumpy, if not will try again.

The question is whether the stream of sparks remained completely steady, Paul: not whether the intensity may have varied, but whether instead of looking at a steady stream, you were looking at a ragged stream - which would indicate misfiring due to spark insufficiency. It may not be easy to tell.

Hi Grumpy, have done it again and yes there is a constant steady spark.

I have been thinking of what i wrote yesterday and i am thinking i was jumping the gun,, it wasnt until the motor was coughing/spluttering wanting to shut down did the spark lost some of its intensity.

I'm not clear on what you mean, Paul. If the engine is running at the same speed, whether or not it is coughing and spluttering should have no effect on the stream of sparks. Does the spark lose intensity when it begins to cough and splutter, but always has full intensity when it is not coughing and spluttering?

Hi Grumpy, yes thats right. When the motor is running smooth there is no change in spark, only when the motor starts to cough and splutter will the spark loose intensity, you have to look hard but you can see it. There is a difference between the "good" spark and the "lost its intensity" spark.

Paul, I suspect that the "loss of intensity" is that the spark becomes intermittent. With the engine running at 2-3,000 rpm you can't see individual sparks, it looks like a continuous spark. In other words, your problem now might be ignition failure.

I suggest you disconnect the kill wire at the ignition module, checking the module's grounding and the gap between module and flywheel while you are at it. Then repeat the test with the in-line tester. If none of that makes any difference, it will be time to check the module's primary and secondary resistance, and/or look for a spare module.

Hi Grumpy, sorry for time limit, am snowed under at moment.
Have not connected kill wire on ingnition module since you asked me to remove it. Have repeated test again, some outcome.. Modules grounding is good and gap to flywheel is good, couldnt get it any smaller if i tried. Have tracked down another module, hopefully will be able to give it a try in next day or two. This should let us know if my original module is no good.

That is the best way to find out, Paul, I agree. I don't know why the spark intensity in the tester would vary when it plays up if there isn't a spark problem, but there have been so many twists and turns in this investigation that I think the only way to go, is overwhelming evidence.

Hi Grumpy, sorry been a bit long, but after reading this you will understand. ( hopefully like me you will let out a bit woooohoooo )
Put on other module i told you about and tried to run the motor, guess what, jumped to life straight away. From idle up to not quiet full revs, didnt want to stress it out to much. This was done with no governor linkages attached. Attached all linkages to carby and gave it another run, from idle up without any sign of hunting/coughing, nothing...
So i thought maybe the motor is trying to trick me so i let it sit till the next day, tried it again, whammo, up and running like it had never stopped..Done this for five days straight, each test went for upto 20-25 mins.. Let it sit for two days no test, tried again, whammo, up and running...
So it seems like all this time it has been the ignition module giving me trouble. Talk about a long stroll through stressville.
Should i now connect all unattached peices now and see how it goes.

I think it all makes sense, Paul. Essentially, I think you had two problems in succession.

First, in the long ago, you acquired the engine with a worn-out decompressor pin. In the first part of this thread, that was replaced and the decompressor then worked.

Second, while testing the decompressor, you fitted the engine to a different ride-on which had a mysteriously malfunctioning engine. You hoped that, because the Tecumseh was running by then with its new decompressor pin, it could be a suitable engine for this second ride-on, which had a chonda copy of the Honda GXV390 engine in good condition except for a malfunctioning ignition module. The Tecumseh soon malfunctioned on that second ride-on, and you resolved the problem by disconnecting the ignition kill wire. Meanwhile the chonda engine worked perfectly once it was removed from that mower. So, it seemed highly probable that the second ride-on had tenant-improved wiring which may have been doing something like applying 12 Volts to the kill wire. With its kill wire disconnected, the Tecumseh engine worked well for a short time, then malfunctioned. The malfunction was somewhat erratic and intermittent, which made diagnosis difficult. Ultimately, having established that nothing else was wrong, you tested the spark while the engine was running. It turned out that the spark quality was changing when the the engine malfunctioned, suggesting that the ignition module had been permanently damaged by its time with the tenant-improved kill wire connected. So, you tried another ignition module, and the engine then operated correctly, supporting the theory that the original module had become damaged.

This has been one of our longest threads ever, and I think easily the longest thread ever that was solely concerned with fault diagnosis. Just in case there is yet another unexpected twist or turn in the case study, I'll leave this thread open. Since it will be open I suggest that you use it to trace the actual wiring fault in the ride-on mower. If you give us a full identification of the mower, we can try to get hold of a wiring diagram, and start making some tests.

Hi Grumpy, sorry its been a while again,, but have finally found the wires at fault.. I did track a mower down, exact same model, motor, everything the same,, except this one ran properly. After a number of days tracing wires here and there and everywhere, the only difference between the two mowers wiring was ,on mine, the wire that came out from under the flywheel had actually been joined up with the wire to the ignition module,, on the donor mower it was not. Other than that, there is no difference at all. I set up my wiring the same way and with fingers crossed tried to start the motor. Kicked over first go, ran beautifully from idling all the way to full revs. Again left it for a day tried again, same result, ran perfect..
I cant believe that after starting with a simple problem of a decompression unit, we ended up on a couple of months wiring hunt.

I would like to thank you heaps for you help on this one Grumpy, it is greatly appreciated.

Hey, it all worked out in the end, Paul, which means the whole process was a pleasure.

I haven't seen the wiring diagram, but it sounds as if that other wire from the flywheel area was the alternator/generator output, so as expected, the previous tenant was applying 12 Volts or so to the kill wire whenever the engine was running. The world is full of people who don't know there is a difference between magneto ignition and Kettering ignition: cars need 12 Volts on their coils to run, so mower engines must also. I wonder how he thought it started, if it needed 12 Volts on its coil for the ignition? Oh well, as a rule of thumb, never expect previous tenants to have been logical.

I'll close this thread.