SR50 MT/Piaggio Typhoon installed 70cc kit, now won't start

[thach2264]

I got this in a trade, said that scooter is running fine with 50cc. Since upgrade to Malossi 70cc, have never got it fire up yet.



There’s fuel = wet spark plug

there’s spark ⚡️ but won’t fire up not even for 1 cycle.



noticed that air is sucking and pushing out of intake. When spray fuel into intake and try to start, you can heard that it wanted to fire up but more like a miss fire and when the miss fire happen mist or white smoke come out of the intake. Also installed a brand new Techingas GP4 exhaust



please help check of the timing/chain time are set correctly. I’ve zero knowledge on timing.



also which do I set first if it’s incorrect, the stator timing then the chain time or the other way around? I see the line or mark on the chain time, but have no idea where's the marking on the stator timing look like.

[aeroxbud]

Your best is to try and find a Vespa manual for the same engine. We never got the four stroke typhoon here in Europe, and I can't find a manual.
You should have set the crank to TDC before taking the old cylinder off.
You could always try putting something like a cable tie down the plug hole to feel for top dead centre.
There is a mark on the four stroke Vespa which lines up with the pickup and the flywheel. You might find one of the marks on the flywheel lines up.
Then if it's the same as other Vespa, the two holes should be set horizontal with the line in the cam facing up.
I can't guarantee it will work though. As never worked on one of these before.

[thach2264]

After removing the head to look into farther, found that one of the valve is bended. Timing is confirmed to be correct.

[GrumpyUnk]

If the valve is bent, you will have to get a replacement, lap it to the valve seat, re-assemble, and adjust the valves.
The hint was the air pumping back through the carb. That indicated the valve was not sealing. That can also be caused if the valve is adjusted too tightly which would keep it from closing.
You could have bent the valve if you rotated the crankshaft with the cam out of time, which caused the valve to be opened when the piston was too high in the cylinder and bip, bent valve.
tom