Dear All,

I am currently flying a Phoenix Topstar 60 without cowl on a OS75AX 2 stroke. As per the design of this plane, the engine is mounted inverted.

In the recent, I have had a lot of issues with tuning the engine. It either cuts in hower or in straight and level at 50%. We have tried manuplating both the needle as well as the low end screw to no avail.

Someone of the field mentioned that 2-strokes are difficult to tune inverted. Is this the case? Should I mount the engine at 90 deg? (will have to modify the firewall for the same)

Ameyam

<span style="font-size: larger;"><span style="font-family: Comic Sans MS;">Ame ... all engines are hard to tune inverted especially when the tank is located above the carb. That causes some problems. For me there is no real issue when you start to tune her properly. So far all my inverted engines never had any real problems and I never once moved my tank. If you can, try to use a plug with an idle bar, it helps. The Fireball brand has an idle bar. Of course mounting it sideways helps a lot for sure.</span></span>

It make no difference in my 12+ years of this hobby having an inverted mounted motor never made any difference. i think its more about tank placement more than the motor

I had the exact same problem with my 55AX in my Inspire (this is with a Perry VP-30 pump).

Tried an F plug, which has a heavier element that stays lit longer.  It worked awesome, and I have a very dependable engine now.

Try the F plug, I'll bet it straightens everything out.

Cody