YS-80 wont start up

[jcclair]

My YS 80 wont start when I changed all the fuel lines and changed the plug . It tried once and wont start up
What could be wrong ? :?

[WayneBrown]

there are a few things that could cause this:
1.)Old fuel trapped in the lines
2.) fuel residue (oil) has blocked lines
3.) Check valve installed incorrectly.

I'd bet if the engine sat for a month or more that the fuel has evaporated, and left a slug of oil in the lines between the regulator and carb, or internally on the regulator.
Use Isopropyl alcohol to flood the lines, start by removing the short line between carb and regulator ( black part at botton of crankcase) and using your fuel pump, pump pure alcohol into the inlet line of the regulator until clear fluid runs out the short line. Do not apply a lot of pressure, just ease it until it flows.
Let this sit 5-10 minutes and reverse the fluid out until the lines are clear.
Oil will return to suspension with alcohol and when you drain it back out, it clears the slug.
Add fuel to the tank, connect all lines and try to start.
if it doesn't fire right off, check the check valve, even at the slow speed of a starter, you should hear a pressure release when you pull the line off the check valve.
If the valve checks out, remove glow plug, hold throttle at Wide OPEN and hit it with the starter for a bit. Close throttle, clear with starter and replace glowplug.
If it starts now, it was a blocked orifice between the crankcase and regulator.
When you have to store it again, run it dry first.