upgrading with big bore kit

[bobian81]

has anyone on here any experience of upgrading a chinese scooter with a big bore kit ?
if so how much better is it ?
where did you obtain the upgrade ?
how much did it cost ?
a few years ago I upgraded a derbi senda with a 90 cc big bore kit and upgraded carb, it really really did turn it from an under powered slow moped - into a proper powerful trials bike. the beauty of it was from the outside the engine looked exactly the same, conveniently the spanish didnt stamp the bore size on it, so in fact one could still get away with running it as a moped, unless of course you were dumb enough to get caught doing 60 on it round town in which case the law would throw the book at you, indeed that was the fate of the kid i sold it to, I myself never had any hassle, as i used to ride it carefully round town and only open it up on country roads or off road.
I've searched the internet for jinlun upgrade big bore kits and come up a blank

[hypojam]

the gearing on our chinese scoots isnt long enough, even if you do upgrade to an 80cc kit you wouldnt go much faster than 45mph

[chcknugget]

I have a kit and there is quite a difference, but it still only goes around 40mph on level ground. I'm from the U.S. so the seller would be of no interest to you.

[Botanic]

Atleast here in Sweden it is not a problem to get them going 80 km/h (50 MPH). Some people has their going 90 km/h (56 MPH) with the original 50 cc bore kit.
The gearing becomes a problem at around 85-90 km/h.

What you need is a bigger main jet. A new quality belt and a powerbox helps some also.

With a bigger bore kit you will get better acceleration, but probably not much more top speed.
Theres a few on the swedish forums testing 70 and 80 cc kits right now. As it seems now the gearing is a problem. I think there will be a solution for that too soon.

[chcknugget]

Keep me updated. I've been looking into a new cdi (powerbox?) but I don't want to spend $60 on something that produces no real results.

[Botanic]

A new CDI won't do anything (what I know).
A powerbox is also known as a boost bottle. A boost bottle can be bought for 20€ or so from for example mopshop.de.
You get the best result by doing one yourself with the right size for our engine. It is quite easy to do it seems. I have not (yet) made one myself.
It is actually just an empty bottle between the carb and the engine. The only "bad" thing about it is that you have to drill a hole on the intake.
Here's some pictures: www.baotianforum.com/viewtopic.php?t=750&postdays=0&postorder=asc&start=40
www.gilera-runner.com/anleitungen/boost-bottle.shtml
www.easyparts.nl/showarticles.php3?grouppath=0-121-279-683

[chcknugget]

Yeah, I've heard of using those before. What kind of results are those people finding?

[Botanic]

Better ecceleration, better gas response and better fuel economy.

[hypojam]

can someone explain the "science" behind these "boost bottles" ?

do they use NOS or something?

[BillyGreen1973]

a boost bottle works by keeping the fuel/air mix at a constant preasure, so as soon as the inlet valve opens the fuel/air mix is forced into the cylinder. Normally it's sucked in as the piston moves down. It is very similar to fuel injection, in that its forced into the combustion chamber.

I have several petrol engined radio control cars, and the boost bottle works the same on these engines too, thats where I learned about how they work.

I did think they worked only on 2 stroke engines (RC cars are 2 stroke), but thinking about it the theory works

[chcknugget]

hahaha, wait until you guys see what I'm cooking up as a christmas project. Let's just say it promises more speed for my scoot. It should be wild. I'm sorry you guys have to wait a month to find out what it is though. I'll make a big old post if it works.

[Botanic]

chcknugget, If your project is a boost bottle, make sure that it is the right size. There is a program that calculates the right size of it. There is a link for that program somewhere on the swedish forum.

The boost bottle works for a 4 stroke engine. Not as big effect as on a 2 stroke engine though.

[chcknugget]

Hahaha, sorry to dissapoint you, but this is a mod better than that. I saw your name on the swedish forum, but I can't really read anything else. Let us know if you find more speed discoveries on their forum!

[BillyGreen1973]

Don't keep us in suspense!!

Let the secret out!

[hypojam]

TELL US #taxman2#