Reading needle jets?

[special-k]

I'm fine tuning the vm36's on my 650. It runs fine and starts good but is a little rich at idle. I have two sets of carbs from 650s to scavenge parts from plus my jet box. Anyhow. The needle jet in the bike is a 0-6 and the spare set has Q-5. Are the 5's leaner? The needle on the bike is 6h9 and the spare is 6h4. Idle jets were 20 on both sets with a 1.5 slide in both sets. 180 mains on the bike and 170 in the spare. Ive dropped the pilot to a 17.5 on the bike but haven't ran it yet to see if it works ok. Im hoping it'll compensate for the slide cutaway. The bike is used on 1/2 mile dirt tracks and rarely goes much below half throttle if l ride it rightthanks

 

[5twins]

As you've noticed, Mikuni needle jets use a letter-number code. Higher numbers and letters higher in the alphabet designate larger or richer jets. That means any Q series will be bigger and richer than the O series. The numbers designate sizes in between the letters. Numbers run from 0 to 9, then the letter changes. So, the next size above a P-9, for example, would be a Q-0.

 

[grizld1]

You're a very, very long way from "fine tuning" with that stuff. The O series is way too lean and the Q-5 is way too rich. The 1.5 slides are also way too rich; 2.0 is the fattest you want to try, and you'll likely need 17.5 or 20 PJ with that. Press the Tech button at the top of the page, go to the carb thread by INXS for a link to the VM Carb Guide, and refer to the baseline there. Getting those VM36s right is going to cost some time and money.

 

[special-k]

As you've noticed, Mikuni needle jets use a letter-number code. Higher numbers and letters higher in the alphabet designate larger or richer jets. That means any Q series will be bigger and richer than the O series. The numbers designate sizes in between the letters. Numbers run from 0 to 9, then the letter changes. So, the next size above a P-9, for example, would be a Q-0.

Ok. Thanks for your answer. That points me in the direction l need to go.

 

[grizld1]

BTW there is no P-9. Mikuni NJ's are sized only in even numbered steps, except for 5.