2 stroke troubles!

[neil_s]

I think it's a fuel problem. The mag is a simple flywheel job with nothing complicated to go wrong. The Vire 6 I had used a Tillotson diaphragm carburettor - is it a similar model on the 12? If so, the diaphragm might have developed a small hole and need replacement. This was a common fault with my Vire 6. Indeed - it might be worth checking that the crankcase pressure pipe is OK.
Best of luck with your engine!

Neil

 

[earlybird]

. The Vire 6 I had used a Tillotson diaphragm carburettor - is it a similar model on the 12? If so, the diaphragm might have developed a small hole and need replacement. This was a common fault with my Vire 6. Indeed -.Neil

I had a 7, similar carb. to the 6 AFAIK. The 12, which is a pumped up 7, has a quite different carb. with a float chamber.
Agree that the OP's troubles sound like a fuel problem, but I wouldn't rule out a weak spark. The trouble with such simple engines is that there's nothing to go wrong!!

 

[oldharry]

Inbuilt in the mag. its true purpose is to Flick the rotor during starting, thus giving a slightly more voltage during start up. If its got dirty it may not be in the run position and CAN affect the timing.

Not on the Vire engine. It had a simple flywheel magneto about as subtle as the old Seagull outboard.

 

[Grajan]

Is it a tillitson? carb ,was used on chainsaws at one time and spares were cheaper from a chainsaw dealer providing you new what you were looking for! In my experience the symptoms you describe can be caused either by blocked fuel jets or passageways /moisture in fuel, (but they will normally run but run ruff with these conditions) or more probably a hole or an air leak in or at the carb diaphragm . fabulous wee engines when they are running but they don't half try your patience when they go wrong.