I am having trouble with a 78 express the moped is in real good shape but I can't make it right. When I brought the bike home it would start by spraying fuel in the carb and I started there by cleaning the carb. It ran and I drove it up and down the street to set the mixture I was close and it died wouldn't restart. I cleaned the carb again and it started but smoked and blew oil I thought I had killed it but had a guy with more experience tell me I still had carb problems and it wouldn't lean out it was too rich. I cleaned some more, and got the same result. I switched carbs and the same smokinging mess. I then swapped engines, and the one that's in it now will start on the first try but dies shortly after. there is some mystery fluid that runs out of the exhaust and from my auto experience looks like oil and water mixed sludge. It leaves the same nasty sludge on the plug. It won't restart unless I let it sit for an extended period and then does the same thing. I haven't checked the compression on the one that's in it now but had 90 psi in the original smoker. If there is a remedy for either please let me know before I try to find a new piston and rings.