Hi everyone - I need some help with a YS 91 AC engine.
I have two of these engines however one of them I can't seem to get running correctly.
I have replaced all the gaskets, checked the glow plugs, checked the fuel tank, checked the one way valve, adjusted the tappet settings and TRIED to follow the directions as far as setting the low/high end.
The problem I have is that I can get the engine to run on high end without a problem, the idle seems to be a little difficult but when I think I have it, I cannot transition to high again, the engine sounds like it is starving of fuel when I go to high.
Any ideas on where to start or what to do?
Then engine is practically new, I have run it about 20 times but always had a problem so I don't want to use it anymore - I think I would just like to get rid of it if I can't get this thing running.
Any help would be greatly appreciated.
Thanks

I don't know if you have referred this to the YS forum but I would. Dave Shadel, the moderator and importer, should be able to help.

Your mid range is too lean. The big brass screw is there for you to adjust it. Try turning it 1/4 turn at a time counter clockwise to richen it up a little. This is a classic problem, and I don't know why so many people are afraid to turn the regulator.

I have the same engine in US60, I sent it to YS for other repairs and a general re-build, Dave and the gang returned it to me in top shape and All I had to do is adjust the big brass screw a tad and that was it, I would either call YS or post this in the YS forum and they will help, the big brass screw should be about flush with the aluminum housing

As stated, the regulator screw allows one to adjust the transition.