Yamaha Neos YN50 50cc bogging down

[BadHarry1942]

Hi hope you can help with my problem. My Neos 50cc YN50 has started to bog down and go around 10-20mph when it use to top 40.

I went out one day then on the way back bog down.

I thought this may be rollers so changed the variator and snapped the crankshaft so total engine rebuild but problem is still there.

So new engine, crankshaft, piston, head, variator, clutch, springs all good as is the belt. Engine pressure 170psi. Carbs cleaned and also swapped to be sure. Fuel supply good, no air leaks as best I can tell, also checked the fuel cap breather. Plug is good also swapped that still Good.

Put the bike on the stand and it will start with one kick and tick over nicely. Turn the throttle and it will go like hell, no problem there.

Get on and ride it,,, 10-20mph,!!!!

Tried removing exhaust, checked air filter all good.

All I can now think of is HT lead\coil, did a resistance test and seems ok, as I say runs like hell in the stand.

Then there's the Stator and the CDI.. not sure what to do here.

What am I missing? Any pointers please because this it driving me nuts.

Thanks, PS. Bike is 2015.

Just to add, if you have a long straight the bike will get to 20mph ok and then slowly slowly with make its way to about 35mph, but I do mean slowly

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[Sacha]

Hiya Harry!  you may have better luck getting a response if you pop over to the new member section and post an introduction.  Welcome aboard!