just installed a 80cc big bore kit and want more speed
 

Hey i just a installed a 80 cc airsal big bore kit in my Baotion Retro (BT50QT-11) scooter, it has the 139 qmb engine btw.

Going up hills and acceleration has improved a lot, but i would like to make it go faster i got maybe a 10 km/h speed improvement after i installed the kit.

What should i do buy a new carb or just install new jets if so what what size would you recommend? thinking about buying some roller weights as well but not sure which ones to buy, it got 7g weights stock. i am supremely fat and weigh around 300 lbs btw. any other suggestions to make it go faster? :thanks:

Maybe you need to lower your expectation, of what such a tiny engine is capable of doing. You have to know how many rpm's your engine is producing at top speed, before tuning your cvt....so, do you have a tachometer? One would think that if it came stock with 7 gr weights, that after a bbk install, a heavier weight would be ok. But this may not be the case, considering your size.

So is it cranking out 8000 rpm's at top speed.....or unable to reach 6500?

IMHO, you need to look here:http://www.partsforscooters.com/Stre...gines-Complete
You can get a new 150 cc motor for $415.00 to $425.00 you'll have the power you need.

First a 150cc engine will not bolt into a 50cc chassis. next its actually pretty simple to get more out of those engines.

Yes knowing the rpms is a good point but you can do a lot with these little engines once you know. The next changes I would make are for airflow efficiency a stock cam is at its limit at 80cc. I would also look into a performance exhaust and into either retuning (rejetting) your carburetor or getting a retuned (rejetted) carburetor. Then I would look into performance variators most performance variators have different ramp profiles from stock and thus change the way it shifts with the same weights. At this point you may wind up hitting redline too easily and if you ride mostly on the FLATS you could look into regearing. If you deem regearing to be the right option regear to a taller gear for flats (numerically lower ratio) it may feel stock again or slightly sluggish off the line but will have a higher top speed (of course it depends upon the engines actual power output).

Having installed literally dozens of bbks on 139, 1p40, 157 and 152 engines, as well as being extensively familiar with all makes of scooters since I built my first Lambretta in 1988, I will now state that achievement of any flat land speed of over 5Omph on a 73cc 139, is pretty good, and about all it will do.

Mods help the 139 gain acceleration, but really don't do anything to the top end. A 73cc engine is approximately 4cid, or 1/3 the displacement of the cheapest lawnmower available at Wal-mart.

To assert the modified 139 is capable of speeds in excess of 55 mph on flat ground, is untrue, and unrealistic.

unfortunately I have to disagree because mine did 50mph clocked by gps, chase cars, and a police radar gun going up a 4% grade and that was only at a 47mm bore with only a 1500 rpm gearbox side cvt spring upgrade, but without improving the cylinder heads flow characteristics, without improving the lean factory a/f ratio (stock carb), without regearing, without a full synthetic motor oil, and without retuning the engine side of the cvt. Now if you had ever tried increasing the engines pumping efficiency you would find that indeed you are wrong and that you really need to learn how to correctly optimize an engine. I trained in college and yes I have a degree in auto, diesel, and industrial applications including high performance and how to maximize any engines overall performance and longevity.

You're all kinds of wrong. I really wish the admins would stop letting you post bullshit.