I have a Fuji 50 that was converted over to ignition before I bought it and it has a vibration around 1/4 to 1/2 throttle. It seems to be smooth at idle and at full throttle but vibrates quite noticeably in that throttle range. Right now I am running it on a test stand before I put it in an airplane because when I bought it, it hadn't been run since being converted so I wanted to make sure it runs fine. I'm using a 20X10 prop.

The engine came with a Mezjlik 20X10 which I'm assuming it was run with and when I first tried to run the engine, I used this prop and the engine vibrated quite a bit more at this throttle range as well as full throttle and later I found out the prop was out of balance. I should have checked the balance before I ran it but I didn't.

If the previous owner ran this out of balance prop, could this have damaged the engine? Otherwise, what could be causing the mid-range vibration?

Thanks.

Shawn

Did you make sure the hub of the prop was balanced also? Just balancing the tips of the prop doesn't cut it once you get above big glow engines.

We'd not know what you mean when you said your engine was "converted" to ignition before you purchased it. ALL of the Fuji-Imvac engines are gasoline-fueled, ignition engines. None of them need a "conversion" to ignition.

Many two-stroke engines will have RPM ranges where they are less than smooth. That's normal. They are usually balanced to give the least amount of vibration possible, but single-cylinder engines just cannot be balanced to be smooth in all RPM ranges. A vibration-isolating engine mount is recommended.

I would guess you meant converted from ATM (magnito) to Electronic Ignition... I have a new Fuji 50 EI which is factory equipped with Fuji's Electronic Ignition in place of the magnito ignition. Regarding vibration, All single cylinder 2 stroke engines have vibration somewhere within the RPM range. You can minimize this effect with a well-balanced prop. Also, use larger diameter props to keep the peak RPM down. I have had excellent results with a Three-Blade prop to minimize vibration. I you use a SPINNER, it needs to be balanced also.

Try a HYDE mount!!!
they are awsome