bigger carb question

hello. new to this forum. I recently bought a '82 honda st 70. It ran many years ago according to previous owner. So far i have removed carb and fuel tank to clean both. i can order an aftermarket carb to fit machine just fine, but i wanted to see if it was possible to put on a bigger carb to increase power. From what i have read online, 22mm carb is largest that would work, but i dont know where i can find one to fit. Also would i have to replace the intake manifold as well to accomodate the carb? any help is appreciated. thanks

I strongly suggest NOT to go with an aftermarket carb.
Air and fuel leaks, poor performance, impossible to set up correctly, no or few spare and customization parts...
22mm (REAL diameter, often these 22mm aftermarkets are as small as 16mm venturi size) is way to big for a standard ST70 head.

The best out there is the PC18 Kehin kit.
Everlasting performance!
If you don't want to spend that much, save some money and buy an aftermarket manifold.

thanks for response. on another dax forum, they recomment a bigger carb to get more power out of 70cc motor. what would happen if i put a 22mm carb on it with different manifold?

Excessive fuel consumption.
That's about all you'll notice.

Note that for example a Shengway 22mm is only 16-18mm, Walbro 20mm is only 18mm and so on.
Those brands are the only decent, reliable Chinese carbs.

I´m in the same position as the O.P. Also 1982 ST 70 (in my case French model)

Did I read you right? Would just a larger dia intake manifold make a difference, even if only minor? I´m not prepared to fork out much more on this one. Not even sure I´m going to keep it much longer - I´m not happy with how it performs. 60 - 65 kph (indicated) on a good day and it takes forever to get there. I had expected a little more, even if not much.

/Sture

thecxer wrote:Did I read you right? Would just a larger dia intake manifold make a difference, even if only minor?

No. It won't make a difference on the stock carb.
Your bike is quite easily tuneable. But... you're looking at around 400£ at least to get it over 90kph.

Thanks, Waynus!

/Sture