When you say you're using 140/42s, are they keihin or dynojet sizes? Looking at this chart https://www.jetsrus.com/FAQs/FAQ_mik...ihin_sizes.htm, if they're Keihin sizes, you're about equivalent with my 132s. However as you're running the full system it could be slightly lean for you although I can't imagine you'd be more than a couple of sizes out.

 

Bought this kit: https://www.ebay.co.uk/itm/184072969953
Suspect its Keihin sizes, however, since my bike has been runnin stock jets with this exhaust kit since the last 15 years according to the former owner, and running well. well untill the fueling got extreme last summer, i went with mild fueling upgrade.

DETAILS...
Pilot/Slow jet
Overall length 28mm
Thread size 6mm
Head size 5mm

Main jets
Overall length 8mm
Thread size 5mm
Head size 6mm

 

Ok well the pictures of the mains in that listing are definitely genuine Keihin. That being the case a 140 is almost identical to what I'm running so you should be really close. Only unknown is that full system - is it a 4 into 1 or a 4 into 2 into 1?

Cheers
Dan

 

Its a 4-1 system

 

My gut feel is you'd need a couple of sizes bigger with a 4 into 1 as they tend to flow more up top.

 

Yeah well im gonna let the dyno tech determine that, im aiming for a 12:1 AFR at WOT, with it being leaned out at part throttle (eg pilot jet)

Considering this ( https://imgur.com/a/MunMKFY ) is my reference point, anything is better lol.

 

​​​​​​Oh yes, richer than a Saudi Prince! Hope you don't think I'm interfering but 13:1 will give you max power on one of these, 12:1 is quite rich on a high revving bike engine.