I had very similar problems with my 140 sport engine during the summer. Very unreliable running all the time. Rpm waving up und down just like the engine was running lean, but surely it wasn´t. I tried to adjust the regulator and main needle and there was no help for this. I then checked everything: Tank and fittings, carburetor cleanliness, everything. Finally I had an idea: Fuel! I have always blended my fuels by myself and this contained 20 percent synthetic oil called Aerosave, which is a german product. 20 percent nitro and the rest methanol. Worked very well in usual engines I have had over the years.

I then tried similar blend with Klotz heliglow blended 20 percent as recommended. Klotz is very different oil than THICK Aerosave; its a low-viscosity oil and worked out very well indeed!! Now these engines are very easy to adjust and runs just perfectly as they should.

So, be aware of the fuel and if there is a doubt, try another blend! The problem may be as simple as that. Ys needs low viscosity oils and fuel to run perfectly!!

Best Regards to all pattern mates in the United States and greetings from HELSINKI, Finland! Check the map if you don't know the place.

Mikko Vuorela