Popping from right side exhaust.

[RcRider89]

The main jet will always be the one over the needle/under the needle ,except down draft carbs(newer supersport stuff). Idle will be the other one in the bowl.
Air jets are another thing.put em back where you found them and 99/100 time you dont have to change em .
You will need to go up in size. I work on too many brands/models/years on a daily basis to keep it all straight in my head, exp small numbers. i dont even remember what sizes are in mine

From stock:
2 sizes up on the main
1 notch down on the needle(or a washer if its not adjustable)
Idle may or may not ok stock
Thatd be my guess to start off

Google motorcycle carb theory. Itll help

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[5twins]

You should really study up a bit and familiarize yourself with your carb set and the proper terminology before you start tearing things apart, lol. If you do have '81 BS34s, the floats will be black plastic and solid so they can't leak. The stock main would be a #132.5, pilots #42.5s, and the air jet a #135. The air jet feeds the pilot circuit and can be changed to help tune that circuit, but it's usually not necessary. Here's a pic with jet locations .....

One up on the pilots and 2 to 3 up on the mains is the usual routine for your carbs. Your needle is fixed and can't be adjusted but you can shim it richer by adding a washer under the fixed clip. One washer is about it because the needle will bind if you raise it too much.

For removing the brass plugs over the mix screws, I drill not quite all the way through with about a 1/8" bit then screw a sheet metal screw into the hole until it bottoms. Then I grab it with vice grips and yank the plug out. A twisting motion helps. Blunt the point on the sheet metal screw too .....

Note the small hole through the brass plug. That's from the factory. Drill a little bit then check that small hole. Drill a little more and check it again. Watch for it to start getting bigger. When it does, stop drilling because you're almost through the plug. It's best not to go all the way through because you run the risk of hitting the top of the mix screw and buggering up the screwdriver slot on the top.

 

[5twins]

The small balls and springs (should be 2 of each) act as detents on the choke rod .....

They can be inserted through this hole ......

I have a special tool for this. It's an old spoke with a dimple drilled in the end. A dab of grease on the end and the ball sticks right to it. I grease the spring too.

 

[RcRider89]

^ thats what I was waiting for lol well done as always

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[barelycompetent]

That really helped. Ok so my main jets are 142.5, I have not removed the pilot jets under the rubber plugs yet so I dont know what they are. I only found two of the little balls, and one spring, gonna have to go back and look to see if that spring is still in there, or where it might have fallen out too. The floats are black plastic, so these are a set of 81 Bs34 carbs. I will drill out the brass plugs tonight. Now when I pulled my plugs both sides were completely fouled out, and this was after the bike had been idling for 20-25 mins. Im assuming the whole circuit is rich with the current jetting. Im gonna clean them really well, and order up some new parts for them so I can start trial and error on dialing them in. Thanks 5twins, the pictures really helped, I was getting sloppy last night, and once you start down that slippery slope of frustration its time to set them down and walk away lol. At least its too cold for me to be out riding right now, so that helps a little bit lol.

 

[5twins]

Yes, that missing spring may still be stuck in one of the carbs. They do that a lot. 142.5 mains are a bit large. Most find 137.5s or 140s do the trick. If that P.O. put such large mains in he may have done something similar to the pilots.

 

[barelycompetent]

I will pull the pilots tonight and see if I can make out what size they are. The fact that the PO didnt touch the air/fuel mix screws leads me to believe he just compensated with overly large main jets. So just to be clear so I have a baseline to start with the stock jetting should be a 132.5 main, and 42.5 pilot? so I should order a size up and size down on the pilot, just to be safe, and 135, 137.5, and 140 on the mains? That should hopefully get me in the ballpark. I appreciate the help, a good nights sleep and some good pics and descriptions really help alot.

 

[5twins]

I wouldn't get a size down on the pilots, you won't need that, and I wouldn't get the 135 mains, they're likely too small. Get 45 pilots, and 137.5 & 140 mains. Make sure you get the proper BS30/96 type pilots and not the VM22/210 type. The two types are similar externally but differ internally. They flow differently. You have to use the type your carbs were designed to use and in the case of the BS34s, that's the BS30/96 type. Here's how to tell them apart. The metering orifice is on opposite ends .....

I recommend using only genuine Mikuni jets. The ones used in these carbs are quite common so you may be able to buy them at a local shop. Look for the Mikuni trademark emblem, the "square-in-square", somewhere on the jet to I.D. it as the real deal .....

 

[barelycompetent]

That sounds like a plan to me, I will get some parts ordered up shortly. Thanks again, and once everything is in, I will report back on my findings.

 

[barelycompetent]

Ok just a quick update. Drilled out the brass plugs over the air/fuel mix screws, got a little off on the right side one but found the factory hole again and got it out. Managed not to booger up the tops of the screws that badly, they can still be screwed in or out. Got my pilot jets out and found they are both 45's. So 45's on the pilots, and 142.5 on the mains, with no screw adjustments, so Im guessing I was running very rich. Ok so I dont need to order a different size on the pilots cause they are already one up from stock, just need to order 137.5 and 140 mains, and some bowl gaskets and I should be in the ballpark. I should be hopefully have my parts by the end of this week, and Im going through the carbs completely next weekend with my local contact, with any luck we will have a good enough tune on the carbs to get the bike nice and warm for a compression test as well. Thanks again for the advice, and the patience to re answer the same question over and over again, it is really appreciated!

 

[barelycompetent]

Oh and I found the other tiny spring as well, it was stuck in the left side carb, so Im getting there lol.

 

[barelycompetent]

Quick update and question. Went through my carbs yesterday, cleaned everything up, new bowl gaskets, checked and measured the float levels, dead on at 22mm. Went to put the new main jets in and noticed that they werent the same size heads as the old main jets. So after a little research I realized that I had been sent the main jets for bs38 carbs, the small round head, and I have 34's with the large round head. My question for the experts, would the main jets for the bs38 carbs work in the 34's? I specifically told six sigma that I had bs34 carbs, and the jet sizes I needed and yet they sent me the wrong ones. If they will work I may use them, if not I will be sending them back and starting my waiting game again lol. Thanks for any help or advice.

 

[nj1639]

Look at 5twins post above.
Pull the jets out of the carb and compare with what they sent you......don't judge by them having different heads, could be they sent you the right ones and you've had bs38's in there all along.

 

[angus67]

the size of the head dosnt matter in this case. In some carbs, the large head cant be used because it may interfere with the float action.
Good you found the spring, I had to buy new ones. tiny buggers.
Ive got a 80 with 34's, Uni foams, straight pipes with cheap glasspacks, stock ignition.
my mains are 140, pilot at 46. comp at 150# L/R. runs awesome. Its also bored to 680cc.
Don't buy a rebuild kit, buy the parts separately. You will prolly need idle mix orings too. Don't soak the bodies, it will destroy the throttle shaft seals. use carb cleaner cans, blow out with compressed air, wear eye protection.
on compression(correct me if im wrong, Mr. 5T) But I think you can get away with a 10 point difference, as in 150 left and 140 rite. Your breather -agreed you have some blowby. Or you have too much oil, and its misting out. oil level should be in the middle of the marks, with bike level. At least that's were mines at, no probs yet.
Good luck.

 

[barelycompetent]

I did pull them out. What I had in the carbs were large head 142.5 mains. What I was sent were the small head mains, and according to all of my research the small head mains are for the bs38 main jets, and bs34 air jets. I have compared them and that was what I came up with. The pic above is for the pilot jet which was actually correct for my carb, I have the 45 pilot BS30/96.

 

[5twins]

Yes, you should have the large round type mains. They hold the needle jet in the carb body once installed so I think that's why Mikuni chose this size/style. The larger head will hold the needle jet in better. In a pinch, I guess you can use the small round type. The threads should be the same so they should screw right in .....

However, there is another main jet out there for Keihin carbs that looks just like a Mikuni small round main but has a different thread pitch .....

These will screw in but feel like they're cross-threading. Maybe that place you ordered from double screwed up, sending the small head style AND Keihin jets as well.

 

[barelycompetent]

Thanks 5twins, the jets that were sent actually threaded in no problems. I just didnt know if they flowed differently or not. To clarify this is what I had in the bike, my pilots were 45's and the correct type for the carb, as verified by the picture you sent, and my mains were the large head 142.5's. The pic is hard to tell, sorry cant really get a better close up, but the jet on the left is what came out of my carb, and the jet on the right is what was sent to me. According to mikesxs pictures and descriptions the left jet is the proper one for my carb and the right jet is for the 38's or the pilot AIR jets on the 34's. I think I am just going to return them for a full refund, and order up some proper jets from jetsrus. I went with six sigma because I had good experiences using their jets in several sets of kehein carbs. Cant really say to much bad about them, a good company, and everyone makes mistakes so I would still do business with them.

 

[5twins]

Yes, you've been sent the wrong type, and in fact, they may not be the small round style but rather a type that Mikuni just calls a "Round" .....

Note that both the small and large round types used in the 650 stock carbs have a line etched around the side. The plain round type doesn't and I don't see that line in your pics. When you order, verify by jet type number, which is the N100/604 for the BS34s. As I've mentioned, these are a very common jet. The large round main is probably THE most common Mikuni main used. You may be able to find them at a local shop. Just be sure to look for the trademark emblem on the jet head to insure they are genuine .....

 

[barelycompetent]

Thanks 5twins, they are in fact just the round jets, no line marked on them at all. So just to satisfy my curiosity, these jets cant be interchanged with my carbs? I ordered some 137.5, and 140's from jetsrus, and made sure they were the correct numbered ones N100/604 for my carbs, they also were sold as genuine mikuni jets, so I will see when they get here.

 

[barelycompetent]

Also I am starting at 2.5 turns out on my mix screws, if memory serves me correctly, once I get the proper jets in these bikes usually run best between 2.5 and 3 turns out? Just to double check. Thanks again for the info.