I am running a 102.5 high speed jet in a 30mm Mikuni Carb on a 250cc GIO badboy quad. When i check the plug after a high speed run it looks fairly white and I am wondering if I should try some larger sizes.

The stock carb had about a 90 or a 95 HS jet. When I bought the upgraded Mikuni carb it came with a 100 HS jet. The largest I had is a 102.5 and thats what worked with the stock carb so thats what i tried.

is there a formula for choosing jets? I read that you multiply the throat by 4.1-4.3.

So, 4.2*30mm= 126 !!!

Is it possible that these companies(like GIO Kazuma, etc) are selling these things with the std "100" jet becasue that's what Mikuni ships out as a default in their carbs?

100-102.5 seems a far cry from 126.

Anyone else jet a 250cc?
Any suggestions?

 

Hi Bud
new to the forum


your 125-126 is just a guide with saftey in mind, i think your best bet will be 105

i will be putting a mikuni 30mm on mine in a few days and will let you know my findings

I also have contacted oko carbies aswell and i will be trying to put 1 of these in 1 of my atvs aswell, just waiting on oko to get back to me today

 

The 102.5 seems pretty good right now I have gone on a couple of long rides, one on a 40 deg C humidex day andno overheating.

Interested to hear what the 105 is like.

 

the 105 will only make your motor run cooler as it flows more fuel therefore little less power