2 stroke cranks  By  geo49 (Read 1,302 times)

Yes, need to split the case
Alleyoop

I don't think I want to go that far right now since the scoot doe's run well.
But would like to cruise without being WOT all the time and maybe get up hills without loosing speed.
I already changed to a sport pipe, up jetted and did the rollers and springs and am now thinking about a BBK.
Any idea on a bbk that would increase power and not have to change the crank?
I have ridden some scoots with bbk and didn't seam to have the power of my 50cc scoot and am trying to avoid a kit that will cause no increase in power or make it feel like it's slower than it was as a 50cc.

At this point I'd rather not swap out cranks, since it only has about 1400 miles on her.
She doe's run well but I'd like to get a little more top end.
I top out at about 42 -43 MPH .

squish head or hump type head.
whats the difference ?
I already added a pipe and changed rollers and springs with great results.
I also up-jetted the carb. and open element filter.

Geo49 have you made any mods at all to your scoot ? When I bought my 2T first thing I replaced the 68MJ with a 75MJ and replaced the standard NGK with the iridium one . It would always hit 45 MPH ( on the speedo ) and sometimes 50 . It would max out at 8k RPMS while riding . On the CS I revved it up just for a fraction of second to see if it would go beyond 8K . If I went down hill and if it went above 8K RPMs it would stall and fizzle .

I decided to get a racing CDI that did not have a rev limit . No diff at all on top end with the same 8K limitation . My dealer said maybe I should try lighter rollers . I removed and weighed them to be a starting point . They were 6G . I tried some 4Gs but it over revved on takeoff and lost top end . I mixed them up to equal 5G and it was a hair better on take off with as much top end loss as with 4G . Hitting 45 is quite good as many modded 4ts can not go that fast . Here is two links on derestricting and tuning www.scootnfast.com/scooter/Tuning_mods/De-Restricting.htm and www.provoscooter.com/tuning

I pulled off the 49cc engine and noticed the exhaust port was D shaped instead of being fully ported out like the BBK is with a O shaped exhaust port . I had read a great 2T exhaust thread by Brent " The 2T God " and noted that he said many stock pipes are limited to 8,500 RPMs , sport pipes around 10,500 and the expensive pipes 14k and up . I had bought a PM Tuning racing pipe that I first tried to fit on the 49cc engine but I could not get it lined up . With the BBK it lined up the first try . The exhaust places a more important factor on a 2T than a 4T . I had a Honda CR 125 that wasa beast and one day a buddy accidentally spun a rock into my pipe and busted it . Man it killed the power big time . I had a buddy weld it up but it blew out the weld as the metal was no good . A new pipe and it was a wheelie machine again . The PMT pipe I lost bottom end since it was unrestricted which did allow for backpressue to build up . Midrange and top end it was a screamer . I replaced the PMT with the stock pipe and it had more bottom and midrange and was much quieter . The stock pipe has a reed valve just before the expansion chamber than released exhaust at 8k RPMs back into the airbox . I had already removed the airbox to use a Uni . I first ran it with the reed valve uncapped . I noticed it got louder at 8K and the powerband dropped a hair . For now it is taped up but I will do a permanent cap off soon .

When it was stock is was not a fast off the line like a buddies Honda Elite but I would smoke him at midrange and top end with ease . Once I got going past 45 MPH it was screaming , even uphill with a running start I got hit 10,500 RPMs and not able to push it hard down hill . I will have to get some taller gears so I can cruise at 45 or more without having it scream and guzzle up gas . I did put in 8g sliders since I figured it would lower the RPMs compared to the 5g rollers . I put in 1.5k Hoca clutch springs to help on takeoff . With the PMT pipe is was not as peppy on takeoff but with the stock pipe I can make it jump even with heavy weights and 13 wheels instead of 10s .

You can also try a larger diameter variator as I will be doing myself . The larger diameter and steeper ramps can often help on the top end .

Mine also gotten faster after 1,000 miles since the piston moved easier than when it was tighter when new .

To truly get more power a BBK is a for sure improvement . Since it is newsih I would enjoy the 50cc engine and do the BBK later on

You have no real need for a new crank, unless there is something wrong with your current one.

You will get the best bang for the buck with a new cylinder/head. And it is much easier to do.