70cc Piaggio Zip AC, lack of power

[wallzip]

Hello all,



I rebuild my engine from 50cc to 70cc. New cylinder, new crankshaft and bearings. Removed the startermotor. The problem i face now is that there is no power at all.



The engine runs fine at idle but the acceleration is pretty weak and it only goes to 40km/h. The color of sparkplug is gray. I couldnt ride that much because of fine tuning everything.



I lowered the main jet from 100 to 90 because in beginning the engine was stuttering. That problem is now solved. I have already changed the sparkplug and the ignition coil. Piston etc. mounted correctly.



I still think there is some problems with the ignition. Maybe the stator coil isnt 100%. I m not sure.



What could be the problem?



My setup:

70cc Athena racing (0.6mm squish)

Athena racing exhaust

Polini CP 21 carburator (new) - 90 main jet

Polini power fitler

Malossi overrange pulley (purple contra spring)

Malossi clutch (white springs)

Malossi wingbell

Polini hi-speed variator (4.2 grams)

Polini evo 3 half pulley

NGK C4 race ignition coil

Thanks

[pinkscoot]

It's nice to see another Piaggio owner here. What are your RPM's at WOT. 4.7 might be just a bit light.

[wallzip]

Nov 25, 2020 17:23:26 GMT 1 pinkscoot said:

It's nice to see another Piaggio owner here. What are your RPM's at WOT. 4.7 might be just a bit light.


Thanks! I love Piaggio

Well, have a Zip Fast Rider from from 2005, so i have no dial to read the RPM's. But i can say

that it doenst max its RPM's with throttle fully open.



I think that 4.2 grams is pretty normal for a cylinder like this. Before i swapped to a 70cc i runned a 50cc Stage 6 Racing combined with Yasuni R and i had 4.1 grams in it. The acceleration was pretty good and hadnt problems at all...

[aeroxbud]

Welcome to the forum.
If the plugs grey, it might be lean. Perhaps an air leak somewhere. Did you do a leak down test after building it?

[wallzip]

Nov 25, 2020 14:11:04 GMT -5 aeroxbud said:

Welcome to the forum.
If the plugs grey, it might be lean. Perhaps an air leak somewhere. Did you do a leak down test after building it?

There isnt a vacuum / air leak if you mean the carburator and the intake manifold. When i put my hand on the air intake of the carburator, the engine shuts off immidiately. Also the engine idling fine with a steady rpm. So there is no really indication of a air leakage. Also no oil leaks at the seals on both sides of the crankshaft.

[wallzip]

Hi all, little update.

I think i found the problem. I changed my polini hi-speed vario with a Malossi MHR vario. I changed the roller weights from 4.1gr to 3.5 grams and yes, the full power of the cylinder is suddenly unleashed! When i give full throttle the scooter goes to wheelie mode lol.

Didnt know that the difference of 6 grams (36gr total) in weight could effect the engine that much!

[pinkscoot]

That's good to hear. I play with .5 gram differences and see a difference.

[aeroxbud]

That's great.
Some bikes just love light rollers.