Modern Vespa

So today I put it back together with a known good CDI, Carb, coil and lead. and its still behaving the same way. I am suspecting something more to this. When it cranks it has exhaust coming out but I don't feel anything going in through the open air box and no filter like a bad valve maybe. I need to get a second person to crank while I blow vape smoke at it with the throttle open to see if its drawing it in. The other curious thing is with all of this cranking and starter fluid you would think the plug would be soaked but its dry. Next step may well be pulling the head and seeing what's going on there. All was fine until the petcock and sticky float allowed the gas into the crank case. So possibly the problem is there.

Well I've gotten a lot farther with this. I pulled the head and verified that the TDC mark is indeed TDC. I pulled the cylinder and the base gasket was soaked in oil but solid. When I got the engine out and was looking at the cam gear I saw the decompression controller. I wasn't aware they were on the leader engine. At rest they open the exhaust port a crack to make it easier for the starter to crank. I saw the spring just not fully hooked but caught on the Allen head screw that holds it together. This meant that it didn't have full pressure to hold the exhaust valve open. Thats why I got 150 psi compression. with that working I should have had a much lower compression. It's why you can't really do an accurate compression test on these or the Quasar engines. I can't remember if the S50 had one. The spring holds the counterweight down so that the valve is open. When the engine starts it turns with centrifugal force and closes it down. Could this be the problem? I don't know but it's the only thing I found out of wack. I cleaned it all up and drained all of the oil and cleaned the oil sump out. As I was sliding the cylinder over the piston as I have done several times before the scraper ring broke. I have an order in for all new rings and spring clips, I'll pull the piston and put it in the cylinder first. Here is a picture of the loose spring:

Well its all back together. Its running well so my guess is that it was the spring on the decompression lever. It's a nice little scoot.

Then I put my carb and CDI back in hooked all up primed the carb and started it. I had to readjust the carb but it idled nice. I took it fo a short ride a very short ride I got about a block away and it died with a back fire. fortunately I was up hill from home, coasted it back to the garage put it on the lift and turned out the lights until another day.

Dang. My sympathies...this is frustrating enough to read, never mind how it must be feeling to experience.

Sorry my post was confusing. The Ops scooter is great it’s my ET4 that’s dead now. But I have a clue.

WOW ! Please don't keep us hanging... what's up with your ET4?

Mine wasn't getting a spark so I traced it back to the pickup. The spacing was spot on but no voltage from it. The rest of the stator was good. It got spark but would intermittently miss. I have been busy so its sitting waiting for me to chase the gremlin.