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Interchangeability of carbs and carb rubbers for oil-cooled engines


Dezza

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1 hour ago, Joseph said:

If it's 34 and 36 RS you are mentioning, it's the RS36 and RS38 that both have 42mm stub OD, the RS34 have a 40mm stub OD

(As per www.mikunioz.com who sell the whole range and provide all the fitting dimensions)

Whatever, it's in the table on 1st page :)

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On 11/11/2019 at 4:32 AM, Dezza said:

Mikuni RS 34, 36, and 38s all have an inlet stub od of 42mm

Looks like it's not.

RS34 : 40mm = BST34 and their rubbers

RS36-RS38 : 42mm = BST36 and their rubbers

Still don't get why you're measuring rubbers to figure out what you need rather than measuring BST carb stubs, some of which are identical in OD as the RS and using the relevant rubbers ? And also why incorrect info is published in your "final" guide ?

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  • 6 months later...
On 1/23/2022 at 10:54 PM, Coolwater said:

Where can I get some inlet rubbers for my gsxr 750m 91 model 

 

I think the OEM parts are no longer available but some dealers may have NOS (????). There are pattern rubbers for several other oil-cooled models but I have never seen them for the 750l,m only for bikes that take BST36s. Rubbers are available for the 1100m,n, but these take BST40mm carbs so may be too big for the 750. Also, the 750 rubbers are shorter than those for the 1100 so even if 1100 rubbers accept the 750 carbs you are likely to run into clearance issues. The only alternative is to keep looking for a NOS or secondhand set. Secondhand 750l,m rubbers do crop up every now and again. If you make 50 posts here you will access the marketplace and can post a wanted ad :)

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  • 4 weeks later...

Bought a set of cheap, £20, 750 Teapot inlet rubbers from Eblag to try with the RS36's .

Lovely and supple and seem to be ok and the carbs fitted with a little grease, a small ratchet strap and a hose pick. 

If you're critical, you might want to match the ports to the inlet rubbers, but there's not a lot in it to be honest.

They do place the carbs closer to the head, but there's still not enough clearance for my application.

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20220221_144010.jpg

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1 hour ago, Pegleg said:

Bought a set of cheap, £20, 750 Teapot inlet rubbers from Eblag to try with the RS36's .

Lovely and supple and seem to be ok and the carbs fitted with a little grease, a small ratchet strap and a hose pick. 

If you're critical, you might want to match the ports to the inlet rubbers, but there's not a lot in it to be honest.

They do place the carbs closer to the head, but there's still not enough clearance for my application.

20220221_144019.jpg

20220221_144010.jpg

What's the problem clearance wise?

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The reason I asked was because I had a fitment problem with my RS38s. This was due to the throttle cable bracket fouling the frame spar. Moving it from between 2 and 3 to between 3 and 4 solved the issue. The carb top fouling is a more profound problem so it sounds like you're going to have to modify your tank :(.

Edited by Dezza
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Motorcycle-Carburetor-Interface-Adapter-

 

I tried a similar set of the chinese inlet rubbers on my DOT head. Same set with 2 that look "normal" and 2 that have mirror images of the part number on the carb end mouth. I never did get them to fit up proper. I ended up getting OEM from the mother ship. eff the chinese.  :L

Edited by slayer61
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Still trying to find a little more info about the GSXR 750W BST 38s to fit an oil-cooled engine?

Did anyone manage it? Is it just a case of casting/ modding some new rubbers? (I’ve got access to a 3D printer that does soft 70 shore rubber) 

Been looking about without much luck and 38mm carbs for a 91 oil boiler, seem like rocking horse shit. 
 

 

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1 hour ago, Digs said:

Still trying to find a little more info about the GSXR 750W BST 38s to fit an oil-cooled engine?

Did anyone manage it? Is it just a case of casting/ modding some new rubbers? (I’ve got access to a 3D printer that does soft 70 shore rubber) 

Been looking about without much luck and 38mm carbs for a 91 oil boiler, seem like rocking horse shit. 
 

 

Keep looking: I have seen a couple of sets go recently on eb@y for fairly sensible prices. Do you have the rubbers for the 91 oil cooled 750? If so, perservere trying to source a set of BST38s spaced for an oil cooled engine as the rubbers are even more difficult to source than the carbs. If you contribute here and reach 50 posts you'll be eligible to post a wanted ad :).

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4 minutes ago, Dezza said:

Keep looking: I have seen a couple of sets go recently on eb@y for fairly sensible prices. Do you have the rubbers for the 91 oil cooled 750? If so, perservere trying to source a set of BST38s spaced for an oil cooled engine as the rubbers are even more difficult to source than the carbs. If you contribute here and reach 50 posts you'll be eligible to post a wanted ad :).

Thanks for the advice they’re on the engine in the Eblag listing so fingers crossed they’ll arrive when it does! 

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  • 4 weeks later...
  • 1 month later...

1100 or 750? I think the 1100 L and K both use BST36s so yes for the 1100. For the 750s, the spacings are the same so with the L rubbers they will go on. They may squeeze on with the K rubbers but you'll have to try and see. The BST38s from the L are fairly tall carbs and the 750K has the DOT head which angles the carbs up a little (see previous pages here) so you may run into clearance issues. Maybe someone who has tried this will be along later with more detailed info :).

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10 minutes ago, Dezza said:

1100 or 750? I think the 1100 L and K both use BST36s so yes for the 1100. For the 750s, the spacings are the same so with the L rubbers they will go on. They may squeeze on with the K rubbers but you'll have to try and see. The BST38s from the L are fairly tall carbs and the 750K has the DOT head which angles the carbs up a little (see previous pages here) so you may run into clearance issues. Maybe someone who has tried this will be along later with more detailed info :).

Thanks for the reply - just to be clear it’s the 750 L carbs going on a 750K 

thanks

 

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  • 2 months later...

So, going by this guide, I went to swap in a set of RS38s into my 92 750N(US) that currently has the stock BST38 carbs. C130A2CB-5E15-40E0-8E80-76594B7EAB9A.jpeg.367fb0bba8962cfd0b066779b4799b0d.jpeg

Not even close to fitting. Pulled my carbs today and measure them and the inlets, even measured the ID on the carbs to make sure they were 38s. My BST38ss carbs have an OD of 46mm, inlets are about 45mm ID. Even verified that I had the stock inlets and those numbers match up. 

Guess I’ll see how worn out the inlets are on the old dot head I have sitting on a shelf, as the slingshot 750 inlets are getting harder and harder to find. 

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  • 5 months later...
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On 1/13/2023 at 3:16 PM, james22 said:

I just need rubbers for a stock 1985 gsxr750 slabby,  the carb has o/d of 40mm that goes into the rubber,    nobody seems to stock rubbers for these, so wondering if bandit 600 or 1200 fit or something, people must be using something else

40 OD is the same OD as BST34 carbs on the 1100 GSXR and 1100 GSXF, so you might be able to use them (the lengths of rubber inlets seem to vary depending on the bike, making carb postioning sometimes incompatible when swapping stuff around). I bought a set of these new not that long ago but not sure they're still available for those bikes either. New is definitely best if you can source them

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