jet size

Batavus Bronco /

Could somebody please tell me what effect changing the jet size on a moped would have on its performance?

For instance, what would be the difference if I went to a higher jet size? smaller jet size?

In particular, I'm looking to improve the low-end performance (acceleration at low speeds).

Thanks for any help you might be able to offer.


Re: jet size

DaveinNaples /

I'm wondering that myself, but from what I've seen don't under any circumstances drill out your jet with a drill, or you screw it (so to speak)

Re: jet size

Ron Brown /

Unless you change something else as well as the jet, exhaust, air cleaner etc., changing the jet will not help. This assumes that the jet is the correct size.

Most standard jets run slightly rich to improve engine cooling and leaning it a bit will give you more power but at the risk of siezing the piston.

If you are not getting "4 cycling" at full speed, your jet is probably ok.

As a quick check, you can turn off the gas while riding and if you speed up significantly just before you start to die from lack of gas, you might try a 1 or 2 size smaller jet but you should allways get a slight increase in power as the gas runs out or you are living too dangerously.


Re: jet size

your jet size determines how much fuel mixes with a certain amount of air. On my batavus bronco i use sizes from 56-59. When you put a smaller jet in your moped might go faster and run a little better, but you have to be carefull not to go too low or you will seize your engine since the fuel is the only lubrication.

Re: jet size

Batavus Bronco /

Ok guys, thanks for the advice. I think I might try to go one size smaller. I'm at a 58, so I'll probably try a 56 and see how that goes, without going any smaller. I certainly don't want to seize the engine.

I'm just really frustrated because my acceleration is terrible... if I'm at an intersection, for instance, cars behind me will honk like crazy until I get up to speed. It's frustrating. Once I'm up to speed though, I go along fine at 30+ mph.

I know nothing about mopeds, unfortunately... still learning slowly!

Re: jet size

I don

Re: jet size

Batavus Bronco /

Yes, I've heard lots of people talk about a bi turbo exhaust... but I have no idea what it is. Could somebody please enlighten me?

My moped is quite old... it's a 1974 Batavus Bronco, so finding one to fit my bike is probably impossible? Or not?



david f martin /

I'd like to try one on my '84 Yamaha QT50, too. Nobody makes aftermarket stuff for my bike, as far as I know, so I'm thinking about possibly modifying one to fit... I'd like to hear from anyone who has done something like this, and how well it worked out...


Re: Biturbo

Here is a good pic of a Bi-turbo pipe

The more your stock pipe has that kind of shape the less difference you will notice.

If your stock pipe is shaped like a box or can... A Bi-Turbo will make a big difference.

And you can adapt any pipe with a shape and size roughly like that one and gain an improvement... but you don't want to alter the overall length more than 2 or 3 inches.

The shape and overall length are the 2 important things.

Don't forget they are louder also.

Re: Biturbo

david f martin /

The first bike looks very similar to mine, sans saddlebags, trunk, etc...

Not my bike, but what it would have looked like new.

My exhaust is shaped like a rectangular can, as you can see.

Is the gold tip on the Biturbo necessary, or just there for looks? I don't really want my exhaust hanging that far out the back of the bike...


Re: Biturbo

That "gold tip" is the silencer... And they are pretty annoying without one.

Like a pretty loud chainsaw... (maybe worse)

To keep it from sticking out the back you might be able to curve as much of the front portion around up front to help out.

Re: jet size

about how much does a buy turbo coast

Re: jet size

bi turbos vary in price. but you need one fitted for your moped specifically. check around. there are other types as well (e.g. leo vinci and polini). i have a polini muffler for a minarelli engine.

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