BB Kit

[marshinman]

Ok all you 4T guys I have a question for you.
I have a Marshin Viper with a 139QMB and I am interested in doing either the 72cc or 80cc upgrade.
I have several questions that I need answers to, so please help if you can.
1) Which is safer/better and more reliable 72cc or 80cc upgrade?
2) What size jet for the carb works the best?
3) Is there any mods needed to be made to the variator.
4) I am also interested in finding out how reliable the motors are after upgrading, is there a risk of destruction, is there any real concerns when doing this, what are the pros and cons.
I most recently replaced the belt and variator and weights and installed a new air box.
I did several tests on the speed and acceleration of my scoot and here is what I am getting on average.
Zero to 35mph on flat ground 6 seconds.
Up hill climb speed 28mph
Flat ground speed over 1/2 mile range 41mph.
Weight of rider not based on average 249lbs.
Should I just leave well enough alone and look towards a 150cc or
is this worth doing without doing any harm to the scooter?
Look forward to hearing what you have to say.

[Deleted]

With the mileage you have on that motor I would strongly advise against building the top end up. It should only be done on crank bearings that are new or near new.

[marshinman]

Good to know that as I dont want to damage it.
So I would be better off to either replace the crank and bearing if I am going to do this or just buy another motor?

[Deleted]

I would find another motor out of a wreck or something and build it from the crank up....and still be able to ride while I built it.

[Deleted]

To answer the other questions:

1) For you I would suggest 72cc
2) It varies but somewhere in the 80-88 range.
3) None other than some 5.5g sliders for best all around performance.
4) A 72cc for your intended use would be fine. Magnetic drain plugs and synthetic oil after 2000 miles will keep the crank bearings happy.
5) Yes its certainly worth doing for your 20+ mile daily commute.

I would suggest a free flowing air filter element for best power.