How to adapt a SBN 44 to a stock 38? 650sx Manifold?

[Shifty]

Can this be done? This is a bone stock 650sx. I havn't had them in my hands yet, but was wondering if this is common practice? I figure I could drill/ tap for the new stud spacing and match the opening of the manifold to the carb. with a die grinder. Just wanted to see if this has been done before. This ski is my GF's and she is having it painted, so I fugured I could do the stock exhaust mod to it and ad this SBN that I have to get some more juice out of it.

Thanks for the input,

Chris

 

[Waternut]

Well I know for sure that it's not standard practice. I just ordered an SBN 44mm for my 750 and I plan to use some 1/8" aluminum sheet laying around to fab up an adapter plate. I figure I'll use a countersunk screw head to mount the plate to the manifold and then an appropriate sized nut and bolt for the carb. My only concern is what the extra 1/8" spacer will do.

Just for your own reference. You may want to only do one at a time. That way you can ensure each work properly.

 

[azreark1]

well your biggest problem would come from the drill/tapping of the manifold for the new studs...you would have to fill the old holes in (i would weld them) but the intake manifold is a cast (alum i think)...and even if it was cast steel it still isnt common practice to weld on cast metals because they become very brittle...after you get the old holes filled in and the new ones tapped then there shouldnt be any problem with opening the throat for the 44 cuz they do that all the time modding 44 and 46 throats.

Next problem...the stock 650's came with Keihn carbs which means if you did get the SBN to bolt up to it the throttle cable isnt going to work so either your going to have to get a diff throttle cable (i cant remember correctly but i think the cables from the 550's with the bn44 work) or your going to have to make an adapter plate which is what i did.

With all that work it might be cheaper to just buy a 44sbn manifold...have you looked into them?

Also you would DEFINATELY want to double check the spaceing of the new stud placement to the outer wall of the manifold and make sure that they are not going to break through from stress or vibration...and your going to want to check the clearance from the bigger throat to the stud holes...

Not trying to deter you from this at all because by all means i love finding ways to do stuff myself that ends up being cheaper than name brand parts...but for some stuff the name brand part is the easiest and cheapest route.

So good luck and let us know how it goes!

 

[Shifty]

Yes, the carb will come later I think. I was thinking of doing something similar if there is not enough meat there. I have someone that may be able to machine an addapter out of billet if all else fails. Though in reality it would work out cheaper to buy the correct manifold and save the head ache. Would this "stock pipe mod" and 38mm (i believe) to 44mm be good solid upgrades?

 

[azreark1]

1/8" aluminum sheet laying around to fab up an adapter plate. I figure I'll use a countersunk screw head to mount the plate to the manifold and then an appropriate sized nut and bolt for the carb.

Are you sure for that adapter plate that 1/8" is thick enough to get the bolts/studs to hold tight? i would think 1/4-3/8" would be better.

 

[azreark1]

Would this "stock pipe mod" and 38mm (i believe) to 44mm be good solid upgrades?

Very good yes, on my 650 i have the 44sbn, pipe mod, and skat 15 prop, and i think the head is milled just a bit and i run circles around my buddies stock 650. Those Keihn carbs just choke out all the potential the 650 motor has...which is a LOT.

 

[Shifty]

I was posting as you were. I Think I can rig up something throttle wise, if it comes down to it I have a yamaha cable I could retro in there. If I were making an adapter I would be using atleast 1/4". I do think if there is enough meat to open up the manifold without interfering with the stock mounting holes I would be good. I think I could fill them with JB weld or Devcon and sand flush. It will be a while as the painter is working on another side job at the moment. I will have to try the pipe mod for sure though.

Thanks allot for the assistance.

 

[tom21]

I plan on making an adaptor for my x-2, it has all the 650 parts bolted on the 750. putting the b-pipe on and switching that keihin for a mikuni and seeing what happens. aftermarket manifolds are not all that cheap. at least to me.

 

[Waternut]

Here is my basic idea. I'm just planning to cock the carb 30 degrees or so, so the bolts would hang over the edge of the manifold.

Keep in mind that I am the king of half bakery and I don't have the mikuni carb so all of this may change once I get it. This is just plan A. I may end up drilling the manifold too but I believe the manifold just has a helicoil or insert. It's not just tapping in the manifold.

 

[Waternut]

Well since I've never delt with dual carbs before I didn't fully understand the concept of a "slave". I just figured it was the same thing on the second cylinder...nope. The one I have now is not a spring loaded butterfly valve, has no throttle cable attachment, and has the idle screw stop ground off of it.

The diaphram looks brand new but I doubt I can even use it...

 

[dbrutherford]

I do not believe it will work. I have had 650's for years and I am pretty sure the bolt spacing of the 44 SBN will be too wide for a Kawie 650 38 manifold. Definetly too wide for a 28mm Keihin manifold!

You do have several options though.

1) If the 650 SX has the old rinky dink 28mm Keihin, find a 38mm Keihin from a 91+ 650 SX. Or use a 40mm Keihin from a 750 SS or SX. These will out perform the smaller carbs hands down. May also consider a Keihin blue 42mm carb. There were two different ones for sale a month or two back.

2) Just try and find a 650 Mikuni SBN 44 manifold. John Ziggler has brand new ones for around 100 bucks. That way you could run any SBN 44/46 or larger aftermarket 48mm carbs.

As for the throttle cable, as long as it is a 650 SX, you simply use the stock throttle cable and brackst. It uses one bolt to mount it to the front engine mount bolt that bolts the bed plate to the engine mount. If you use an aftermarket throttle drum, it makes the swap even simplier. Look to ADA to get one. This is an easy carb swap, I have done it before to my old 650 SX and 650 X2.

 

[wayne]

Can this be done? This is a bone stock 650sx. I havn't had them in my hands yet, but was wondering if this is common practice? I figure I could drill/ tap for the new stud spacing and match the opening of the manifold to the carb. with a die grinder. Just wanted to see if this has been done before. This ski is my GF's and she is having it painted, so I fugured I could do the stock exhaust mod to it and ad this SBN that I have to get some more juice out of it.

Thanks for the input,

Chris

i have a 650 westcoast manifold that takes a 44, for sale.

 

[Shifty]

How much for the manifold... maybe I should look in the "for sale" section.

I dont think she could use the power at the moment really, but I want to mod something becasue I can't afford to hack up my SJ and I have a 44 SBN at the moment. This SX has the 38 Keihin presently and the ski is pretty fast. My GF brother in law works at a machine shop, so maybe he can turn up an addaptor. I just dont want to rag out the stock setup incase it doesn't work correctly. What would the jetting specs be on this thing? The carb came from a stock Yamaha LX 650, and this 650SX is all stock except for the copper head gasket I am running (should be lower compression than stock). I thing it has an aftermarket prop also. I plan on doing the pipe mod as well, I would assume this would have some effect o the jetting. Am I wrong in thinking this 44 Mikuni is set up right the way it is?


Thanks again for the options provided,

Chris

 

[dbrutherford]

Here you go!

http://cgi.ebay.com/ebaymotors/JET-...emQQcategoryZ56422QQihZ006QQitemZ160213229445

 

[Shifty]

That is nice and sure would simplify installation, but I don't think I can afford that at the moment. The ski is getting painted at the moment and I broke her handle pole last summer, so I will be buying one of those soon also. I think I will stick to the pipe mod and move on from there. Thanks for the link though.

 

[dbrutherford]

Keep an eye out. That one is new. You can find them for 50 or less usually. It IS the prime season for selling parts... not buying parts. Over the colder months parts prices go way down.

 

[surfjetlouie]

I have an adapter plate to convert keihins intake to Mikuni 44.
PM me for more detail.

 

[dbrutherford]

Got a pic pf that adapter?

All the adapters I ever saw converted a Mikuni manifold for use with a Keihin carb.

 

[theskiclinic]

I sell the adapters , they run $35 and will mount up to the keihin manifold to mount your mikuni carb

 

[Waternut]

I sell the adapters , they run $35 and will mount up to the keihin manifold to mount your mikuni carb

That's exactly what I was thinking of. A little thicker but very nice. That's a really good price too. Probably cost you $15-$20 in materials if you did a one-off for yourself plus half a days work. If I get another SBN carb that hasn't been ghetto-fied with a hacksaw, I'll be looking at buying one of these.