building a monster. thats my plan....

[brandonscoot]

so i finally got some extra cash on my hands to fix my scooter and bring it back to life. recently i uped the plug one notch hotter just experimenting with tuning and it worked pretty well till i put a hole through the piston. so now im ready for a bbk. i want a 70 or a 90... something beast. wheelie power and the ability to run with a 150.
so what would be a complete package for this?

i was thinking 70cc, big carb, jets, i have a pipe and cdi/coil, prob get a variator, then what else??? i wanna stay around 300 +- if possible....

any advice is appriciated, thanks

[90GTVert]

I see a few basic options :

70cc

70cc sport Kit (Polini Sport, Autotech355, Hoca, etc...) $150

Hoca variator $50

2000RPM clutch springs $10

Assorted main jets $20

Wrist pin bearing $10

Roller or slider assortment and shipping will take up the rest of the $.

Add your current pipe and other parts. Tune the cylinder to work better with your pipe if possible.




90cc Short Case

If it's a short case, browse eBay till you catch a deal on an engine from a 90cc ATV. Sometimes you can catch them quite cheap. The rest will depend what you get/what it needs. Try to find something as complete as possible and in good shape.



90cc Long Case

You would have to be willing and capable of doing all of the case machining yourself to make it work on a $300 budget unless you catch some crazy deals for a big long case setup.

The crank and cylinder could come in pretty cheap or take most of the budget. Depends what you wanna do.

You could try to pick up a deal on a used 90cc stock (50-52mm) cylinder. You should be able to catch that for $50 in usable condition on eBay with time/searching. The idea would be to get something that would at least get you by for some ride time till you could get a new kit / bigger kit. If you're lucky you might catch a cylinder kit in great shape that would last a long time.

The other option would be to go right for a 52-54mm big bore kit. That's gonna cost about $150 from Autotech355, Parts For Scooters , or KaseaParts to name a few. Half your budget is gone there already, and it's unlikely you'll make the $300 mark by the time it runs.

I'd suggest getting a new crank. Splitting the cases and installing a new crank isn't something you want to do a lot. You can pick up a 42mm stock 90cc crank for less than $100 or right at $100 with some looking. You can go with a 45mm crank for just a bit more, probably $125-150. The extra cc won't make a huge difference over what you can do with a 42mm crank (96cc vs 103cc both having 54mm bore), not that every bit doesn't help. Cylinder are meant for certain strokes because of port height and cylinder height so I suggest trying to match up your crank to the cylinder you would like to ultimately use.

As long as you keep everything mild (stock porting) you can probably get away with the stock carb and a stock exhaust so you'd just need to add in the rollers, jets, and other tuning bits. If your pipe has a large stinger diameter it may be able to be used. For best results in the future you'd probably want to get a 90cc pipe, tune the cylinder and trans to match it, and get a larger carb.




All of the stuff from the long case area could apply to a short case as well. It's just easiest to stick to a budget on a short case if you start with an ATV engine.


Any time you buy used to save money, you take a risk.


The 70cc setup is the easy option, and once it's ported you are done till you get a beefier crank, cylinder, pipe, etc... The 90cc option could be an ongoing project. If you built a budget 90 that's pretty much a stock 90, you could later upgrade it with more parts if you desired. Any of this could take a lot of work. Doing the machining yourself is a TON of work and in all honesty I don't recommend it. I have done it once and I don't know if I'd do it again. Clearancing for a crank sucks with a dremel, drill, hand tools. Making room for a big cylinder isn't as terrible, but still takes plenty of time. Of course you could always buy a complete 90cc from Parts For Scooters or ScrappyDog, but that's gonna put you well over budget.


True power wheelies are not easy. You will have the have the CVT and total tune just right to even think about it unless you truly build a monster, especially if you have a longer framed scoot.


I strongly recommend checking out some threads in the Tech Library. Project 90, 90cc Minarelli Swap/ Build, 49-103cc, Big Bore Install, are a few. I'm tired of typing now, but there is a lot of stuff to consider if you really want to get the setup that suits you best. Oh, there's a thread here about wheelies somewhere. Might be called power wheelies? Try using the google search on bottom of the page to search the forum for that.

[2strokd]

Holy cow :jaw: , thats a great answer :bestpost:

[brandonscoot]

so its the 12mm pin, and im gonna go with the 70 cc, variatior, jets, ect.

next question is, what is the height of the cylinder? 64mm or 70mm???


thanks for any help!

[brandonscoot]

or if anyone knows of a kit to just buy, im looking on ebay right now but i cant find the onw i want that comes with the rollers and coil and everything for a 12mm they only have it for 10

[brandonscoot]

also what size is the spindle for the variator on the 12mm kit?

[brandonscoot]

okay okay, so i got the scrappy cast 72cc kit w 47mm bore, 85 and 90 jets, my tuned pipe and cdi coil combo, a new 12 mm needle bearing, gonna pick up some metal files to prep it all, and FOR SURE go back to the original plug. seeing as how the old one caused this situation by burning a hole in the cylinder. then just for quaility control im gonna go premix.

so... im trying to find out:
(1) what size variator to get, the scrappy dog one
(2) is it nessicary to remove the oil pump if im going to premix?
if so how can i get that brass colored thing in front of it off without the puller tool?
or where could i get the puller tool localy? auto zone, advanced, hft?

any help is appriciated, im going to do the transformation this tuesday on my day off when i have everything together. thanks -brandon

[90GTVert]

1) If it's a 12mm pin it should be the larger vari.
2) I guess you don't have to, but I would. Leave the gear on the crank for now and just pull the pump out.

49ccscoot.proboards.com/index.cgi?board=yamajog&action=display&thread=564

[brandonscoot]

okay thanks tons! im gonna order the vari and a performance carb now, and the pump, thats the idea i was thinking too but wasent sure. ill post up some pics when its ready!

[brandonscoot]

also, what should i do with the hole on the carb where the hose went to, leave it open or put a little cap on it?

[brandonscoot]

yay i just got the performance carb 28mm, performance 21mm variator, and performace alum intake manifold with fiberglass reeds... should help a bit! :scoot:

[Reign]

Oct 16, 2011 16:09:57 GMT -5 brandonscoot said:

also, what should i do with the hole on the carb where the hose went to, leave it open or put a little cap on it?

Always cap those when they're not being used. Same with the vacuum port if you switch to a gravity-feed petcock. Any little hole like that is a air leak, and can make it hard to tune.

[brandonscoot]

alright then sounds good. and i got the scrappy cylinder n piston today, i noticed the piston is pretty tight in the bottom part of the cylinder, like there wouldnt be a way to slide the piston through the bottom and out the top, even with no rings... is this normal>?

[brandonscoot]

oh i get it, the bottom was just slightly imperfect, just need to file/sand it barely so

[brandonscoot]

and 90gt, i figured out the oil pump situation, i just took it out, removed the drive gear off the pump and put the pump housing back in to plug up the hole in the block... we'll just say the pulley left in there is a harmonic balancer.... haha