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Troubleshooting Polini Thor 130


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Hey Paramotor folks,

I’ve been flying with a Polini Thor 130 for about two years, and I’ll say It’s run quite well for that time. While it’s had a few little bumps and peculiarities, it’s definitely been better than most 2 stroke engines I’ve dealt with in the past.

I’m a very competent and experienced mechanic, I understand all the present systems pretty well, empirically, and those few issues in the past have given me some good foundation to mess with this thing. I will say I’m not the biggest fan of 2 strokes or carburetors, but I get by.

About 2 months ago I took my first flight of the spring. It went well, started up fine and ran well for ~20 minutes or so. No super high RPMs, nothing unusual otherwise. Towards the end of the flight I started losing power, wasn’t able to get up to full RPMs, slow, bumpy throttle response, etc. It did this for 2-5 minutes, I nursed it as best I could, but it continued to falter until it ultimately died, so I made a quick and easy landing.

Everything that happened felt like a fuel issue, not a spark issue, but you never know. I’ve done a wide variety of troubleshooting since then, and haven’t been able to get even a sputter out of it, which makes me feel like it’s a spark issue, but that system checks out. Wanted to get some opinions, hoping you all might have some insight.

First round:

  • Turns over easily with pull cord

  • Checked fuel filter

  • Checked fuel (two month old non-ethanol, 50:1 oil ratio. I’ve run this thing with year old fuel from this source in the past with no negative effects)

  • Basic carb teardown and inspection (WG-8 Walbro)

  • Reed valve is in fine condition

  • Checked vacuum line to carb, it’s pulsing and clear

  • Checked connection to throttle cable, tried disconnecting throttle, no effect

  • Spark plug is fine

  • Spark is present, used a light up spark tester

  • Compression is there, can feel it, didn’t test it formally though

 

After all this I ordered a rebuild kit (with Spring) from BlueSkyPPG, and the pop off pressure tester.

  • Carb was popping off between 11-14 PSI, with rest pressure all the way down around 4 PSI.

  • I rebuilt the carb using the new parts and spring, pop off pressure is now 18-19 PSI, with rest pressure around 9-10 PSI.

  • I replaced all fuel lines, and the inline fuel filter, 2 were delaminated and slightly coming apart and may have been causing problems.

  • Performed compression test, maintaining 120 PSI after 2-3 pulls.

 

Still nothing. Not even a peep, not even with starting fluid.  Because of this it really feels like a spark issue, but I definitely have a visible spark, both on the tester, and when I pull the plug out and ground it to the engine.  

 

  • Is there a way to quantify spark? I guess it’s possible it’s there but not enough umph.  Is there ever a failure with the magneto system?

  • Open to any and all scientific processes, or wive’s tales, I’ll try anything!

  • Any other ideas of places to post this for ideas?

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I would try a new spark plug, they can break down under compression plus it is a cheap, quick and simple check.

The timing can be out. Either an internal fault in the coil or the flywheel has become misaligned on the crankshaft. Less likely and more difficult to check.

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