I have a 2021 kayo bill 125 (au125-2). Brand new motor. I did an engine swap and replaced spark plug (ngk) new carb. And new battery. I have spark, fuel is getting to carb , but with compression test it has a zero reading. It will crank but not fire. Thanks for input because I’m completely stumped.

 

If you are lucky, someone at the factory has not adjusted the valves properly. If there is no valve clearance, that is probably the problem. If there is a massive clearance, that valve has probably stuck open. Redneck fix, insert a screwdriver blade between valve and rocker, spin engine over, valve is then shoved down more and may free off. Otherwise it is head off and check. Before removing head check valve timing, if it is well out the piston may have hit a valve and bent it so it doesn't close.

 

Thank you so much for the info as I am kinda teaching myself through this. When I rotated flywheel and was at the T Mark for TDC both intake and exhaust valves were closed (seated)?? Are they both suppose to be closed ?

 

"at the T Mark for TDC both intake and exhaust valves were closed (seated)?? Are they both suppose to be closed ?"

Only half the time, check clearances with it at TDC with valves closed. Remove cover from cam sprocket and the cam timing mark should line up with a mark on head. Then rotate flywheel one turn and you will find both valves are slightly open at TDC.

 

Okay I’ve got the valves exposed and at tdc on compression stroke. When I checked the clearance I used the smallest I had which was a 0.08 which service manual says they need to be at 0.05-0.06 ? Could this be my issue ? Also notice tiny tiny metal shavings. In intake side walls. Is this normal for a BRAND NEW motor ? Also might add that I was fixing the break lights and wires touched and blew the fuse. Replaced the fuse and all brake lights now work and still have spark and fuel. Did I damage something else besides just the fuse and that’s why the motor won’t start ?

 

"Did I damage something else besides just the fuse and that’s why the motor won’t start ?"

No, if you have a spark and the engine spins on the starter, it would fire up if you had compression. Metal shavings in the inlet port are a big worry. Slightly too big a valve clearance isn't going to drop compression, it is no valve clearance that makes compression leak through the valves. So, if you are sure your compression tester is correct, looks like you have a major engine fault. Remove head and check valves and seats are OK, a metal shaving stuck between valve and seat would do it. Then remove cylinder and check it and piston, could have broken or wrong rings, or damage on cylinder and/or piston, compression has been leaking out somewhere, it should be obvious once you strip the top end. Get rid of all those shavings before re-assembly.

 

Okay I will double check on the compression. To triple check I am running compression correctly, petcock valve needs to be turned to off correct? To insure motor doesn’t start during compression testing?

 

You won't have a spark plug in when compression testing so engine can't start. Best to open throttle when testing, though that is difficult if you are on your own and have a "shove in" type tester like me. Easy rough check is press your thumb over the plug hole, spin engine on starter, if compression is sufficient to blow your thumb away from hole, you probably have enough for engine to run. It certainly won't blow your thumb off if your zero compression reading was correct.

By the way, an engine will run for quite a while at idle with fuel turned off, as it uses what is in the float bowl.