I know for christmas i will be getting a biturbo exhaust and a performance airfilter but i will need to get a bigger jet right? and if so what size will i need? thanks martin

P.S. I am a very excited 15 year old boy who cant wait to rampage the streets (that was a joke)


If the bike runs lean at top RPM after the new parts are installed you will want to jet upwards. Of course it may run lean at mid throttle and a different needle might be called for too.

Some carbs may already be fitted with a main jet that can handle it.. The stock Honda/Keihin PA50 II carburetor has a #78 jet and an expansion chamber did not make my engine run lean.. it was just about perfect.

Bottom line is to carefully test your new setup with properly done plug chops at various RPMs and riding conditions.. Sometimes periods of leanness are unavoidable and other measures should be taken to protect the engine, like using more oil in the mix.

If you desire top performance some of these tests might show some dangerous leanness but thats the price you pay if you want maximum power.. The edge of too lean is where max-power is.


Martin Read /

its a puch maxi which i am buying these parts for so does this help, what did other people buy, what jet size?

Thanks Martin


Oh.. well, if you use the search link above.. type in

Puch Maxi Jet Size (or similar)

Check Subject and Message Bodies

Select: All dates

A bunch of threads come up.. this is such a popular subject.. general agreement seems to be near a #62 jet.

I was attempting to add something to generic recommendations as far as determining what jet your particular bike needs under your riding conditions and preferences. The only way i know of is for the individual person to test and discover it themselves.


Martin Read /

alright thanks for that, i know i should have used to search, sorry


Here's the thing.. Your air:fuel mixture is influenced by a lot more things than just a number satmped on some main jet.

The mount of oil in the fuel affects how lean or rich the mix is. The weather and altitude affect it.

Jets themselves are supposed to be flow-rated so an accurate number can be stamped on them but who knows how careful the manufcturer was? Some of them just drill a certain hole in a jet and dont flow test it.. they just stamp a common number on it. The same size of a hole is no guarantee that two jets flow the same amount of fuel.

Another thing that affects lean/rich mix is how much air is getting in. An air filter (dirty or clean, big or small, etc) affects the ratio. The carb and intake manifold and intake port surfaces and sizes also have an effect on the mixture..

And there are lots of other things that affect the mix.. So, unless you have the exact same bike as someone else, you should be wary about blindly following someone else's recommendations. Start with the #62 but be careful and do plug chops and protect yourself anyway.

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