Check my jetting, please?

So my plugs are getting black really fast.

I've been searching around and am finding a lot of threads for non-stock 400s whereas mine is straight up stock. I know my float height has been off so I've adjusted that but while I had the carb apart I thought I'd check and see what I have in there is correct as I'm reading a lot of conflicting posts.

81 400SH
Stock exhaust and airboxes.
Large main (9mm length, 8mm head width): 135
Pilot Air Jet (9mm length, 6mm head width): looks like 55 but could be 155?
Pilot Jet, the one under the rubber plug (14mm length, 4mm head size): 42.5

Thanks

I think it doesnt really matter how your bike is jetted, as long as it runs and isnt too lean. It only serves as a good starting point.

What plug you using?

Pic of plug would help. Is the bike tuned up and carbs synced?

Unfortunately I cleaned the plugs with carb cleaner but they were both equally two stroke black. Bp7es plugs. Carbs are synced but it seems like they’re both just dumping gas in. Been cleaned, new needles, mix screw and o rings, bowl gaskets, air jet plugs.

First the left cylinder was not firing, rebuilt carbs, then they both did. I took the carbs off to adjust float level then right cylinder wasn’t firing. I’m just trying to find what the stock baseline should be before I start making any radical changes.

Also while I had the carbs off again I poked around and found the left coil where the plug wire attaches is caked with dirt and rust. I cleaned in there as best as I could but I think I need a new coil. Will check with a multi meter first. Oh well... it’s a winter project!

What are you turning your idle mix screws at? I used at least one pair of new plugs for every jet and tune that I tried. I have tested my bike with about 10 different size jets and put 200 miles on some jets to be sure of the tune.

Are the needles adjustable, if so, set them right in the middle. Turn your idle screws to around 2 turns out, maybe 2.5. That will give you a starting point. Then put new plugs in and go for a few aggressive rides.. Youre supposed to tune by going full throttle and cutting the engine out. But you can do it this way just to get an idea first.

How are you adjusting the float level? Pics help too.

Idle screws are at 3 turns. I’ll take them in a half turn. Not sure if needles are adjustable but I’ll take a look. I adjusted the floats after looking at a bunch of threads here and a few bs34 specific YouTube videos. Ive only got a standard scale so I set to slightly less than 1.1 inches with the little needle spring fully extended.

Do you have foam or brass floats? Brass are 26mm and foam are 32mm from base of carb when measuring.

Brass. So 1.024 inches.

Aha! After some World Series googling I found a post from 2013 by you xschris that gives stock jet sizes and they’re exactly what I have. I’ll double check the diaphragms and needles to make sure they’re set correctly and not damaged.

The info is all in the manuals too. Haynes and Yamaha versions available at the top of the Garage section.