Mikuni SBN 44 models?

[ShreddinSD]

So, I bought a rack of SBN 44s years ago, originally for a triple but now they are getting split up, one is going on a JS 550 With 650 swap and the other two are going on an X2 build. Hopefully. Apparently there are different models of the 44. I have the Mikuni manual and it has 3 different sbn44 carb model #s with different tuning specs for each but I cannot find a model number on any of my carbs. I am sure that someone has done this before and knows which carbs I have. They were probably off a late 90s GP 1200 would be my guess. I was planning on finding right angle fuel fittings, but I’m not sure whether I should get screw in ones or drill and press/glue new nipples? I also need an extended butterfly shaft that I am assuming I will be available from Mikuni. Yes, I’m a cheapskate and don’t want to spend $800 on intake…haha. Third pic is the carb I was running on the x2. I now have a 46 and did not notice much difference with FPP 750 SX, wet pipe and 6° timing advance on a big pin bottom end with bored small pin jugs. 26cc domes for 180psi. I am hoping that dual 44s or SB40i s will give me what I’m looking for.

 

[kevbo]

All the brass fittings press in. If they won’t fit tight enough you can lightly peen around the hole with a center punch. Your OEM 93-94 small pin dual manifold in the picture has larger passages and can be opened to use Mikuni 44s. They also set the carbs farther apart than most aftermarket manifolds. This really helps with getting them mounted. As long as the 44 carbs are the same the pilot circuit will match, that’s the only difference. Other cheap options are any of the OEM 750 dual carb racks. All OEM big pin manifolds have smaller 40mm passages so all that can be used with them is the stock Keihin 40 or mikuni i-40. Both of these carbs work great, the keihins throttle better. In case you were wondering, any stock rack will outperform any single no matter how big it is. If you use 44s they will both need identical throttle plates so buy 2 shaft/plate kits. Expect pilot jets to be around 115 and mains from 110-120. Once they’re set, you should notice better acceleration and same top speed. Their main benefit is no hot cylinder that you always get with single carbs. I tried using a single on 750s twice and burned the front piston both times.

 

[ShreddinSD]

Sweet. I think. I’ve got a couple stock cdk2 racks. One is clean inside and out. Just needs rebuild. I think there was a point where I decided no more kiehin and got rid of rebuild kits and everything. Dang. So if I make it simple and go back to stock carbs should I go up a jet size or see how stock works? I thought stock carb diameter was 38mm and I was doing something going to Mikuni sb40i. I guess I need to try the 44s someday but the stock rack is going back on once it’s rebuilt. The stock rack won’t burn a lot more fuel than single sbn 46 will it? Thanks for the help, not sure why those cdk2 racks went to the graveyard but rebuild kits are cheap so they’ll be back in action.

 

[Alectravis]

Sweet. I think. I’ve got a couple stock cdk2 racks. One is clean inside and out. Just needs rebuild. I think there was a point where I decided no more kiehin and got rid of rebuild kits and everything. Dang. So if I make it simple and go back to stock carbs should I go up a jet size or see how stock works? I thought stock carb diameter was 38mm and I was doing something going to Mikuni sb40i. I guess I need to try the 44s someday but the stock rack is going back on once it’s rebuilt. The stock rack won’t burn a lot more fuel than single sbn 46 will it? Thanks for the help, not sure why those cdk2 racks went to the graveyard but rebuild kits are cheap so they’ll be back in action.

Oem 3 jet Keihin cdk-IIs, 40 mm: 78, 50, 132 jets, 1.6 n&s, 1 turn low screw .5 turn high screws

That is a setup that has worked well for a lot of people in my groups 750's

Try them out and see how you like them, but I'd say just go to the dual 44s if the keihins aren't what you want.

 

[kevbo]

The only stock Keihin duals I would avoid are the ones from the 1995 750sxi, those had a single pilot and smaller jets. All the others had two pilot jets and their main jets are big enough for aftermarket pipes. The only parts Keihins seem to need is the O-ring thats on the main N/S and the main diaphragm tends to leak air through the center rivet. The Keihins from any couch 1995 up will have the narrower intake and the top of the carbs will be smaller diameter than the 93-94 models. I recently installed a 1996 750 sts rack on a 750sx, It occasionally had a slight hesitation from 1/4 throttle. I stepped up the lower pilots one size and am very impressed with its response considering how clean it runs at part throttle. I also have a 750 with a pair of aftermarket 44s that also work very good but aren't any faster. Unless you are racing, the stock carbs are sized about right. Make sure to use a big pin CDI if more timing advance is used. The number on the good cdi will be 3735 or higher.

 

[john zigler]

Not all SBN's are the same. What you have is OEM Carbs, which are totally different than off the shelf performance carbs.