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BDT 38mm carbs on a GS 1150

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    #1

    BDT 38mm carbs on a GS 1150

    I picked up a good set of 1990 GSXR 750 BST 38mm carbs which I plan on trying on my GS 1150 after all the other restoration and engine work is finished. The motor will be a 1229 with Web 340 cams, Web valve springs, street ported head, manual Web CC tensioner, new high capacity oil pump gears, modified clutch basket, back cut trans gears. For now the exhaust will be a new V&H street system. The plan here is not to build a race motor, just a reliable fast street bike.

    Most here will probably wonder why I don't use 36mm Mikuni flat slides. I did exactly that back in the 1980's with my other 2 1150's but decided to try a different way this time. My question to you experienced guys here is how many of you have used either the 36mm or 38mm BST carbs on your street GS's and what do you think of them?

    2nd question is whether to use dynojet or factory pro carb kits on these BST38's ?
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    #2
    I have a set of 36's on my 1100e and it made a world of difference. Throttle response is immediate. Quite a bit of trial and error getting the jetting right but worth the effort.

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      #3
      Originally posted by rwnielsen View Post
      I have a set of 36's on my 1100e and it made a world of difference. Throttle response is immediate. Quite a bit of trial and error getting the jetting right but worth the effort.
      Did you use a dynojet or factory pro jet kit as a start point or just work out the jetting from scratch yourself?

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        #4
        I started with a dyno jet kit already set up with the 36 bst carbs. I fouled so many plugs, so I tried a factory kit . Been running that for years. Can't say I've got them right, but fairly close. I've been through 3-4 sets of emulsion tubes @ $90 a set. They seem to be pretty finicky. Slowly, I've been lowering the float height, close to stock, but not quite. Oddly, the bike with a 1229, gets way better mileage than my stock 1150.
        GS\'s since 1982: 55OMZ, 550ES, 750ET, (2) 1100ET\'s, 1100S, 1150ES. Current ride is an 83 Katana. Wifes bike is an 84 GS 1150ES

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          #5
          Those 38mm CVs from the GSXR750 have big spigots. Have you tried putting them into the carb boots yet?

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            #6
            Originally posted by jimb12 View Post
            Those 38mm CVs from the GSXR750 have big spigots. Have you tried putting them into the carb boots yet?
            No, because I don't have the carbs yet. I bought them from a guy on the GSXR forum and had them shipped to Chris Hunt for rebuilding and sonic cleaning. Enough guys have used them on GS 1100 & 1150's that I am sure the boots will work. Using new 1150 boots so they are pliable.

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              #7
              Why so many emulsion tubes? I have heard that these carbs have problems with emulsion tube and needle wear caused by the slide guides wearing. This apparently causes the emulsion tubes to become oval shaped where the needle rubs.

              Originally posted by Carter Turk View Post
              I started with a dyno jet kit already set up with the 36 bst carbs. I fouled so many plugs, so I tried a factory kit . Been running that for years. Can't say I've got them right, but fairly close. I've been through 3-4 sets of emulsion tubes @ $90 a set. They seem to be pretty finicky. Slowly, I've been lowering the float height, close to stock, but not quite. Oddly, the bike with a 1229, gets way better mileage than my stock 1150.

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                #8
                Exactly. This where I believe all the plug fouling started. I still haven't figured out the correct angle for the carbs. On the GSXR, they're clearly angled, relative to the float bowl. The intake tract is more horizontal on the GS. Maybe it's not a big deal, but I sometimes I get a surge on closed throttle, where the bike lunges forward, like gas is dumping out of the float bowls or that's what it feels like.
                GS\'s since 1982: 55OMZ, 550ES, 750ET, (2) 1100ET\'s, 1100S, 1150ES. Current ride is an 83 Katana. Wifes bike is an 84 GS 1150ES

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                  #9
                  Originally posted by jstewart View Post
                  Enough guys have used them on GS 1100 & 1150's that I am sure the boots will work. Using new 1150 boots so they are pliable.
                  Guys seem to be using the 36s which are different than the 38s. Here's a clue as to the size of the 38s: testing in 1990 GSXR750 intake boots, the Mikuni RS 36/38 literally falls in without touching the sides. RS40 barely touches the sides. I can tell you that it is a TIGHT fit cramming RS40s into boots made for the 36 CVs.

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                    #10
                    i had 38mm on my 1229 efe same sort of set up as you had 150 mains can't remember other setting but i did have to play about with float height cos the carbs sit flat not angled as on gsxr they were really good when set up , good throttle response, didn't use a dyno jet kit std 38mm needles and pilots .changed them when some rs38s came my way cheap

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                      #11
                      I Picked up some 38's and had a member rebuild/jet them. I cant wait to try them. What would be a better pipe to use? Yosh or Bassanai? Motor is stock.
                      Current Rides: 82 GS1100E, 00 Triumph 955 Speed Triple:twistedevil:, 03 Kawasaki ZRX1200, 01 Honda GL1800, '15 Kawasaki 1000 Versys
                      Past Rides: 72 Honda SL-125, Kawasaki KE-175, 77 GS750 with total yosh stage 1 kit, 79 GS1000s, 80 GS1000S, 82 GS750e,82 GS1000S, 84 VF500f, 86 FZR600, 95 Triumph Sprint 900,96 Triumph Sprint, 97 Triumph Sprint, 01 Kawasaki ZRX1200, 07 Triumph Tiger 1050, 01 Yam YFZ250F
                      Work in progress: 78 GS1000, unknown year GS1100ES

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                        #12
                        wrong info,the above mentioned carbs are 36's.When mounting these carbs, do you need to make a support brkt for the rack? Or can they be held in and supported by the carb boots? What about clearance issues with the cam chain tensioner? Sorry if I am hijacking the thread,feel free to tell me to start my own.
                        Current Rides: 82 GS1100E, 00 Triumph 955 Speed Triple:twistedevil:, 03 Kawasaki ZRX1200, 01 Honda GL1800, '15 Kawasaki 1000 Versys
                        Past Rides: 72 Honda SL-125, Kawasaki KE-175, 77 GS750 with total yosh stage 1 kit, 79 GS1000s, 80 GS1000S, 82 GS750e,82 GS1000S, 84 VF500f, 86 FZR600, 95 Triumph Sprint 900,96 Triumph Sprint, 97 Triumph Sprint, 01 Kawasaki ZRX1200, 07 Triumph Tiger 1050, 01 Yam YFZ250F
                        Work in progress: 78 GS1000, unknown year GS1100ES

                        Comment

                          #13
                          Originally posted by limeex2 View Post
                          wrong info,the above mentioned carbs are 36's.When mounting these carbs, do you need to make a support brkt for the rack? Or can they be held in and supported by the carb boots? What about clearance issues with the cam chain tensioner? Sorry if I am hijacking the thread,feel free to tell me to start my own.
                          No problem, I am interested in any comments concerning BST carbs used on GS 1150's or GS 1100's. I am particularly interested in the 38mm version because I hope they will provide a decent increase in performance over the stock 36mm CV's on the 1229 I am building. I have two main concerns with these carbs.
                          1. Reliability since they have a reputation of wearing the slide guides and the loose slides cause the needles and emulsion tubes to wear out.
                          2. Tuning setup particularly the float setting since these carbs were not intended for a side draft application.

                          Comment

                            #14
                            Originally posted by jstewart View Post
                            No problem, I am interested in any comments concerning BST carbs used on GS 1150's or GS 1100's. I am particularly interested in the 38mm version because I hope they will provide a decent increase in performance over the stock 36mm CV's on the 1229 I am building. I have two main concerns with these carbs.
                            1. Reliability since they have a reputation of wearing the slide guides and the loose slides cause the needles and emulsion tubes to wear out.
                            2. Tuning setup particularly the float setting since these carbs were not intended for a side draft application.

                            Did you ever get the carbs on and running? And if so how do you like them and what are you running for jets and needles and where did you set the float height?

                            Comment

                              #15
                              Originally posted by Joe H View Post
                              Did you ever get the carbs on and running? And if so how do you like them and what are you running for jets and needles and where did you set the float height?
                              No I didn't. The 38mm GSXR carbs I purchased on the GSXR forum were completely disassembled and sent directly from the seller to a carb rebuilder trusted & recommended by members on the GSXR site including the seller. The rebuilder condemned the carbs as being so worn they were not worth investing any effort or more money in. I contacted the seller through the GSXR website and told him what the carb rebuilder he had recommended said about the carbs he sold me. No reply from him after he talked to the recommended carb rebuilder.

                              I decided to stick with what I know works and bought a new set of MIC 36mm flat slides.

                              I have had a spotty experience buying used parts from members of forums as opposed to parts from sellers on sites like Amazon.

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