ys56 help

[Dave81]

Hello,

I have a used ys56 that I rebuild but it goes super lean each time it transitions into the mid range. I rebuilt it with a new piston, ring, liner and check valve. I have tried running it as rich as possible on the needles but the issue persists. The whole engine has been taken apart and cleaned and looks ok.

When I remove the line from the tank side of the check valve I do get a small hiss to suggest its been pressurized ok, no leaks anywhere. The only thing I can think of is the regulator/carb being at fault. I've checked the regulator and all parts look fine and undamaged although i'm unsure how all the parts in the reg are supposed to work.

Any advice appreciated before I bin it!

Dave

[ChadL]

What do the needles look like? If the needles have ever been over tightened closed it can put a groove in the needle and change the orifice shape in the carb which can cause the condition you describe above. I had a YS 91 3DS that did exactly as you described. Once I replaced the carb I got "normal" tuning.