Runway

Hi Bax
I've just bought a second hand OS 91fx two-stroke in excellent condition. However, I'm told there was a design change to the carb housing by OS some time ago to get around possible problems with overheating/bubbles in the fuel line.
How can I tell, please, whether I've got the older version or the newer one?

Thanks.

Perminator

In the old version the whole remote needle valve assembly was a part of the rear cover. The new one has a brass arm which holds the remote needle valve assembly and there's a plastic housing for the needle too. In short, if you can remove the remote needle valve assembly without removing the rear cover, you've got the new one. If not, the parts are not very expensive and are easily obtained from Tower hobbies, for example.

Perminator

On the old ones the rear needle valve assembly was a part of the rear cover plate. The new ones have a brass arm that is bolted on to the rear cover plate and the rear needle valve assembly is mainly in plastic. The brass and plastic are to reduce heat conduction and by that eliminate the bubbles in the fuel line.

So if the rear needle valve assembly is bolted onto the rear of the engine you're safe, otherwise you can just order the parts from Tower hobbies or something. Just look the .91 FX up and the parts will be listed at the bottom.

Runway

Many thanks for that.

Bax

My Feedback: (11)

The newer version has a black plastic needle valve holder that's on a bracket that bolts to the rear cover.

Runway

Many thanks for that, Bax

Runway