Large Model Association Forum

Information required on an old OS 40. If anyone can help please email me at gerard.2@virgin.net.

What the heck Gerard.
If you want help you are going to have to be rather more explicit in your request than that.

Hi Tony,
Im trying to tune an older moodel OS40, ( before the FS max series,) and I dont think it is delivering enough Rpm / power. This is the engine you flew for me at Binham, which was since set up by an `expert` The two screw adjustments on the carb are difficult to set up in sympathy. I dont have much of a clue with this motor, as to setting it up, perhaps you can give me an idea if you know this model Just Engines seem a bit of an overkill for this problem. Its also a lot more difficult to start than it was at Binham.
Regards Gerard

Gerard- if this is an old OS Max, then the needle is probably worn, making it difficult to tune. They leak air into the spraybar, sometimes a bit of fuel tube over the threaded part can cure it. If not, you can get a new one from John D Haytree, tel 01626852330. He stocks parts for all engines.

Thank you Bob, I`ll try that
regards Gerard

Have you changed fuel? If the engine has been run over its life time then it will have been run on castor based fuels (Good ole days ) I've had issues in the past when switching to bekra (fully synthetic). They need about a gallon through them running rich to clear out the carbon deposits from the previous fuel. Even then they don't clear up completley.
Also not sure on that model but OS went through a stage of using air bleed carbs, worth checking if it has one as that could be partially blocked, remembering the mixture adjustments is the opposite to a normal carb.
Hope that helps

Andy Wynn

Thank you Andy
Gerard 4001