Need assistance with unexpected issus AMT600

.I'm normally good at diagnosing and fixing such mechanical issues, but have never needed to repair anything in the running gear of this vehicle and do not know this engine at all. The original equipment one-cylinder four stroke looks like it may be a Kawasaki or Yamaha.

After sitting completely idle for several months, it would not start but would fire/run very briefly with a shot of ether. Detected problem to be no fuel delivery, checked fuel line/filter for flow (good) but no fuel flowing from fuel pump. Replaced vac tube to pump - started and ran for a few minutes at idle minutes - then quit. No fuel from pump. Ran engine with external fuel source (gravity fed) - no fuel from pump. Bought and installed replacement pump, ran with external fuel source. No fuel from new pump.

Ran engine and checked vacuum at the port (assume port comes from intake manifold) - no vacuum. Revved engine up a bit with vac port open - engine spit motor oil from port.

I have no diagram or blow-up drawing for this engine. Is that available here or elsewhere?

Is there another vac port somewhere else on the engine? Is there a crankcase vent somewhere that might need to be unplugged? It is difficult to imagine that, suddenly, there is high compression of the crank case (major blow-by or hole in piston, etc) or intake valve problem. But, maybe so.

What does your experioence say about absence of vac at manifold port and spitting oil from port? All ideas and critiques are welcomed.

Also suddenly, this engine has developed a "no crank with switch" starter issue - will crank if I hot wire it - so will do a separate post on that.

I have replaced 2 ignition switches I'm not familiar with your model but I would checkon my 825 on. e came from amazon , piece of junk so I bought a factory switch , have had no further problem, as for your model , I'm not familiar with it but all systems have a pcv type valve and a closed vent back to engine, I would check for a Manuel for info on this system, and check valve and vent sounds like you bare building pressure up for some reason