Starter Won't Turn Over

[atvopa]

I'm working on my grandson's go-kart. I believe it's a KANDI 110, but I'm not sure.

The starter motor wouldn't turn over. I removed the spark plug and checked compression, which is good. I also got spark on the NGK plug.

Without the spark plug in, the starter motor would turn over quite easily. However, as soon as I reinstalled the spark plug, the starter motor would drag and wouldn't turn over.

I bought a new starter and solenoid relay thinking the old ones had become weak. Even with the new starter and relay it wants to drag and it won't turn over.

I thought perhaps the battery was too weak, but a brand new battery results in the same non-starting behavior.

Is it possible this is a timing issue? Am I missing something obvious?

Thanks in advance for any advice.

 

[atvopa]

Update: I measured the compression on the engine and it appears to be max. at ~30 psi.

My previous "check" with my thumb and visual inspection was in error.

It looks like I may have a piston or valve issue.

Time for a re-build.