OS 55ax mucky fuel

[Bob Vaughan]

Having just fitted a newish OS 55ax to my Acrowot I appeared to be having running problems that I suspect were fuel tank related, which upon removal, has quite a bit of rubber bung stuff floating at the bottom. Its very possible that some of this junk has migrated up into the carb and is causing the poor starting / running problems, any tips regarding cleaning the carb out as I've not taken this type apart before.

thanks Bob V

[john stones 1 - Moderator]

Take carb off and remove needles and flush it all out with fuel Bob. If you have manual it has exploded diagram, if not it's on web, also needle settings, take plug out as well check for gunk in engine

John

[Bob Vaughan]

Thanks John........I bought it second hand without the manual and now having looked on line there's everything I need.

Thanks again,

Bob

[Engine Doctor]

Hi . When you strip and clean the carb make sure you dont forget to remove the screw in fuel nipple . The chamber behind that will hold bit of debris . Its often overlooked as the nipple appears clear and blows through ok but when reassembled the bits move and block the jets , so remove and clean .Its happened a few times at our club when a member has said they have stripped and cleaned the carb but it still plays up. Its now the first thing I check. The last engine that had this problem was a Saito . When checked it had some pieces of stuff that looked like carpet fibers !! A decent filter clunk like a sintered metal clunk( by Ripmax or Du-Bro) will prevent this .Hope you get it sorted .

[Bob Vaughan]

Yes, there was some crap in there, it looked like cotton wool fibres or similar, plus some black bits, very small but definitely there. How do you remove the low end needle? I can turn it in all the way but when I open it right out it stops at about 6 -7 turns and is then solid. I 'm a bit worried about putting too much pressure on anti clockwise (undoing further than the stop point ) for fear of causing damage, but logically it can only come out that way?. When I first received it the low needle was about 5 turns out which is a lot more than the manual suggests at 1 and a half turns, that seems to be a big discrepancy!.

Thanks to you both.

Bob

[john stones 1 - Moderator]

The whole unit comes out Bob, loosen the throttle stop screw and it pulls out

John

[Bob Vaughan]

Cracked it, the low needle screws all the way in and pops out where the barrel would have been. I've now cleaned all orifices and passage ways, reassembled, and am ready to go! Regarding the discrepancy between my setting of 5 turns out and the manual's suggested 1 and a half turns out, was that I had not clearly grasped the relative positions of the two components when properly assembled. With the barrel fully closed the correct setting of one and a half turns out for the low needle is very close to where I was originally. As I look down into the carb throat I see the barrel moving across to the fully closed position, and then when opening up fully I see the barrel retracting to expose the low needle. At full throttle the gap between the end of the low needle and the corresponding barrel is about 2 - 3 mm. Anyone with an OS55ax and 40k carb that could confirm this gap please?.

Thanks

Bob