Carb advice

Anybody Know how a 166-p8 needle seat compares to the O.E.M. 166-R2 ? Halls has no R-2 in stock. Will try a bigger idle jet to see if it helps initial throttle bog. If jetting changes don't show any improvement , will have a leak down test done, don't have what's needed to do it here. engine showed no signs of external leak.

Needle jets go in alphabetical order, lower is leaner, and within each letter they go numerically lower is leaner. So it goes Q-6, Q-8, R-0, R-2, R-4, R-6, R-8, etc. P-8 is way too lean. Get needle jets from eBay or you can order them from any motorcycle dealership, have them look in the Western Powersports or Parts Unlimited catalogs.

The pilot jet has no impact on initial throttle bog, the pilot jet ONLY impacts jetting at idle with the throttle closed. As soon as you crack the throttle slide open even the smallest amount, now the fuel is metered by the slide cutaway, needle jet and needle position. If you have a bog an initial throttle opening, one of those is what needs to be changed, assuming there is no air leak.

I am almost 100% certain you have an air leak.

Kartwheel , Thanks for the explanation of letter / numbers sequence on the needle jet. Received bike with the wrong jet. Will try to find the R-2 and change out & adjust.

googled "mikuni needle jet chart"
first result


you do not need to buy parts a common mikuni part from a supplier like halls, any online carb shop has them. these vm roundslides are very common, plentiful parts.