Valves?

Cam gear worn or damaged?

Check the backplate and the rotor...Make sure the rotor is not dragging causing excessive heat. Also make sure that the rotor and the pin holding the rotor in place are tight...I had the screw back out and the rotor was loose...no damage but the rotor would work its way into the con rod and cause excess drag

Check the pump passages...now be careful there are a couple of tiny springs and valves in the pump mechanism...

Make sure the Diaphragm on the pump is seated and not damaged...I have seen some where the Diaphragm with is also the gasket gets sucked in and leaks air.

Look for air leaks in the backplate, carb assembly....


Look at the Throttle barrel in the scroll and look for crap or debris here.....

Bearings? are the bearings smooth If there are not excess heat can cause problems

Check the pump and make sure the pushrods top and bottom will move the pump mechanism smoothly....

Look at the top of the pump assembly where the machined aluminum housing fits the pushrod...Is it worn....?

Glow plug? When the motors are new the plug can go as they break in. Just because it glow's doesn't mean the plug is good.

Exhaust system clean and clear.....I have had issues where a restricted exhaust system...Like crap in the pipe caused the motor to heat up and loose power when things got hot.

Throttle servo is OK?

Throttle linkage is OK? If the linkage or servo is not solid it could be causing it to die off at idle....On the top end the barrel should be vertical..and not past...Sometimes they can over-rotate slightly and this causes the motor to go lean and heat up...If using a Hyde style mount the motor will move forward slightly as it throttle up....This movement forward can cause the barrel to over rotate.

Lets see what else...Bad fuel? tank setup?, tank problem...?

I know this is a lot to look at but.....Without playing with the motor I have no idea....basically I have given a list of lots of possible ideas.....Some I have seen with YS motors and some I have not...not all of these issues have been seen on the DZ but its the way the motor functions.....These are tiny little machines and yes they need to be taken care of..and fed well...

I hope you find what's wrong....

Troy Newman