maustin

My Feedback: (7)

I recently obtained a used YS 170 DZ (non CDI) and the motor runs rough at idle and will not idle down past 2250 rpm and will not cut off when carb is completely closed. Idle stop screw is way out BTW. I put a new O-ring set in and valve cover gasket but no luck. The motor will not die without throwing a rag in the prop. It just sits there thrashing about until either the rag is used or I pinch off the fuel line. Never had a YS do this so looking for suggestions to try before sending to YS for a overhaul.

Thanks for any ideas !!

maustin

My Feedback: (7)

Followup: Had some time to look at the motor with cowl off last night and discovered fuel around the valve cover gasket but overall the engine was dry. I'll resurface the cover and adjust the tappet clearance while I'm at it as I was unable to get the .002 feeler gauge under the adj nut. I hear no air leaks otherwise.

Dave Harmon

The best way to adjust the tappet clearance on these engines is by feel.
This is because after some running....the rocker arm has a increasingly deep recess worn into it by the valve stem...a small amount for sure but this recess prevents accurate clearance adjustment when using a feeler gauge.
You want to feel a small amount of movement.

Dave Harmon

The engine is sucking air from somewhere or there is air in the fuel line(s).....or a pinhole in a fuel line on the engine.....look for bubbles in the fuel line.
If you are using a crap trap type of fuel filter....remove it...they leak and admit air to the fuel line.

If the engine is mounted in an airplane...first I would use an outboard fuel tank and new fuel line everywhere on the engine and try it again.
If it is still bad....take a look at the needle valve assembly and remove the brass needle valve housing and replace the O-ring.
Be sure the housing is tight.

It is much easier if you mount the engine on a test stand....you really need one if you are going to use YS engines!
Once on a test stand....put some fuel or rubbing alcohol in a spray bottle....start the engine and get it into the failure mode...ie...at idle with the carb closed...
If it is still running as you described....while it is still running....spray alcohol around all areas that have an O-ring or gasket.
When you find the area that is sucking air....the engine will suck in the alky and go immediately rich then speed up again to the RPM it was at previously.
You will probably have to get the bottle very close to prevent the prop blast from blowing away the alky......flood it on there.

maustin

My Feedback: (7)

Thanks for the advise Dave. I may have finally discovered my issue on this motor. Got out this morning and ran the motor after making the above adjs to the valve clearance and valve cover. Left off the cowling and put the plane in a cradle upside down so I could see what was going on while running. The motor ran like crap as usual but I noticed the valve cover was leaking from a spot on top that had been scrapped down by a nose over previously. Only a pin hole but fuel and bubbles coming from it like crazy. The rest of the motor was bone dry. Now to get a replacement valve cover and see what happens!!! Onward through the fog !! LOL

Dave Harmon

Great.....
You might try sealing up the hole with some thick CA as a test to be sure that is the entire problem...before you order parts!

maustin

My Feedback: (7)

Good idea !!!! Thanks

maustin

My Feedback: (7)

Final Report: After sealing the hole in the valve cover with CA I ran the motor again this morning and by golly the motor ran like a champ. Solid predictable idle and steady top end. The kill switch I had setup for killing the motor after flight on asphalt runways worked great. Thanks Dave for your input and using CA to test before ordering parts.


maustin
YS Motors - Love em or list em !!

Dave Harmon

Great!
I like your line about 'Love em' or list em'.....
These thangs are kinda like wimmen....they are always at one extreme or the other....never anythang in the middle!!
Glad to have helped out in some small way....have fun!