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Thread: Gs odd ball carb question

  1. #1
    Join Date
    Feb 2018
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    Caboolture Queensland
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    20

    Default Gs odd ball carb question

    just joined but have got an education off this site with this gs cheers for that ,

    the help i need is a question of carbs I've gone though as much as i can looking for info on a unbiased option on carb choice,

    I've got a 1982 gs 850g shaftie with 997cc top end fitted 1050cc pistons it got upgraded cams and I'm running bs34ss mikunis which I've ditched the air box (I know shoot me now) but its what i want for the look of the build i cut my teeth on tuning them to put the "compromise" in ride around spot of the power curve , i grew up tuning dirt bikes so I'm no expert but i build my own motors because i wanted to learn plus its cheaper. so the question is I've sourced a donor gsx750 1985 "slabby" i pinched the front end for better braking- handling and a little lower look but mainly got it for the VM29SS FLAT SLIDES ( not smooth bore and not 28mm) they got acc pumps . i know i can just get a set of 36--38 rs mikunis new from tom at mikuni oz. but i want to do things my way theres a story to how i got the 85 gsx and the rest of the bike went to bloke with my same way of thinking.
    I've heard of blokes machining them out to 33mm not gonna do that.
    so to the question--- if 28mm smooth bores were the ducks nuts in the day on the gs1000 79 will i be able to get the VM29 flat slides to out perform the vm28ss smooth bores???? I know they are gonna be better than the bs34ss cv's (don't shoot me for that i love the cvs but doesn't suit where I'm trying to get) i guess i need a unbiased opinion on if spend the time on the vm29ss 'Slabie" flat slides or just get the 38mm RS Rack,
    I've got the 29s cleaned up and i wanted to put them on as i wanted to stay time specific, but if I'm just putting a bandaid on a broken leg??? if so ill just go to the surgeon aka Tom at Mikuni oz and get the 38 rs . cheers lads
    Last edited by gmgs1050cafe; 02-07-2018 at 01:46 AM.

  2. #2
    Join Date
    Feb 2003
    Location
    Brisbane Australia
    Posts
    2,539

    Default

    no such thing as 28mm smoothbores, there are 29mm ones with a 17mm drain plug on the bowl. 38mm RS flt slide be a huge over kill. try looking for some mikuni 33mm smoothbore carbs. thats about as big you want to go on a 1075cc engine. CV carbs are always larger sizes compared to slide carbs

  3. #3
    Join Date
    Jul 2009
    Location
    New Zealand
    Posts
    3,400

    Default

    The gsxr carbs you've got weren't seen in the US - they were rest of the world model carbs on the H and I models of 750.
    Yes, they're tunable. Common Mikuni jets but only two needles ever available for them. a lean one for everywhere except Japan - and a rich one for the home market cos the pilots are achingly lean on those for emissions reasons....I can hunt in my records for the numbers if you need them, the home market ones we saw here were gray imports.
    Another level of tunability is that you can run both, one or no accelerator pumps, simply by pulling the operating rods.
    Worth a crack on the engine you're running, I'd have thought. Probably a better street carb than the 29 smoothbores.

  4. #4
    Join Date
    Feb 2018
    Location
    Caboolture Queensland
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    Default

    like i said sharpie I'm no expert but after an expert opinion .......i can't spell but i can arm wrestle right.... same diff lol.
    greg the ones i got are Australian version as I'm in queensland cheers the numbers i got in these carbs are
    Piolet-20 mikuni
    main 57.5 with a r stamp think they been drilled no stress got a bunch from the bs34 tuning
    needle -6dp3 was on clip 4
    piolet screw was at 2 3/4 turns out


    thought 120- 130 on the mains would be a good starting point as got pods and a 4 into 2 cut down that flows like a 4into 1 built by me
    not sure which needle it is at moment
    but would i be better with the lean needle and inrichin the pilot jet (don't need to pass emissions here in sunny qld cops love the look lol)
    and the other question is will the acc pumps cause havoc on the side draught motor ????
    much appreciated for your wisdom in this adventure....

  5. #5
    Join Date
    May 2009
    Location
    Norman, Oklahoma
    Posts
    24,879

    Default

    Original poster..go to THREAD tools or ADMINISDTRATIVE at the tool bar and move this to the PROJECTS section of the tech forums. This spot is exclusively for our website founders build bike.

    Or maybe the carb / exhaust section.
    Last edited by chuck hahn; 02-07-2018 at 09:52 AM.
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

  6. #6
    Join Date
    May 2004
    Location
    St. Catharines, On.
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    7,645

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    We will need some pics of your hot rod G.
    Welcome to the site.
    2@ \'78 GS1000

  7. #7
    Join Date
    Jul 2009
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    New Zealand
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    Without going to my records I think that's the lean needle. Doesn't matter as most of the response comes from the pilots in these. 20 is pretty standard. Given your biggish motor, I'd stick with the 20's as a start and run the pumps. Mains usually finish up in the 125 area.
    Everything is sized for a 4V head which gives a very strong vacuum signal as soon as the valves open. You're going to get some compensation for the loss of signal with a bigger engine - so don't go too far away from where they are jetted now.
    And yeah, move the thread....

  8. #8
    Art H Guest

    Default

    No Replies? I have a set of smooth bores on my 79 GS1000, they do not have the vacuum port for the petcock so I know they are custom. Anyway the motor is stock except for a 4 to one exhaust and all I can say is that it rips! I picked up the bike for $400 w/ 22k miles, painted it, new continental radial tires and for under $1500 I have a great bike.

  9. #9
    Join Date
    Feb 2018
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    Caboolture Queensland
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    Heres a pic of my gs I've been building20171209_165739.jpg
    Last edited by gmgs1050cafe; 02-15-2018 at 06:45 PM.

  10. #10
    Join Date
    Feb 2018
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    Caboolture Queensland
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