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Mikuni Two-Barrel Carbs

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    #1

    Mikuni Two-Barrel Carbs

    I have a 1984 GS550ES with 25,000 miles on it that I plan to restore.

    I have just purchased a set of Mikuni Two-Barrel carbs for rebuild. I plan to run a Vance and Hines 4 into 1 pipe on the bike.

    Suggestions for jetting, shims, pilots etc ?

    I am also boring the cylinders to either .5 mm or 1 mm and fitting new pistons and rings.

    My compression as it sits is 125 psi hot across all 4 cylinders. Book calls for 142-199 PSI hot.

    The engine runs well, but is down on power.

    Also if I need new cams is there a source for these? Thanks to all. Tom
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    #2
    You have two carbs or they are two barrel?
    1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
    1985 GS1150ES stock with 85 Red E bodywork.

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      #3
      How much power are you expecting ?? It's not a crotch rocket. DID you have the throdle wide open when you checked the compression The fact that it is even across all 4 sounds like the motor is still sound. Have you adjusted the valves ?

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        #4
        If you are going to rebore it why not sell it & get a GS750 A wiseco piston kit & reground cams is going to cost maybe $800

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          #5
          Mikuni Two-barrel Carbs

          Yes the GS550ES is equipped with with two Two-barrel carbs. One feeds cyl 1 and 2 and the other 3 and 4.
          Yep WOT with the engine hot after ten miles of riding. Again I have an even 125 psi compression pressure on all four, however the book calls for 142 psi minimum. A small shot of oil in each bore hot and WOT brings the compression on all four cylinders up to just under 200 PSI so I know that my bores and rings are worn. Next I will do a leakdown test and listen for air in carbs or exhaust to double check my valves/bores. The Vavles were adjusted before the compression tests. I can get OEM oversize pistons for about $60.00 for four, and about $80.00 for oversize rings. I will mike my camshafts when I remove them to see if I need to replace them or have them reground.

          I know that stock the GS550ES is about 60 hp fresh, and I can probably do a little better with a pipe and jets.
          The 550 is actually 572 cc stock and with a 1mm over bore will be approaching 600cc.

          I am just looking for someone on the thread who has run the 550ES with aftermarket 4 into 1 exhaust and find out how they tuned the carbs. Jets Shims etc.

          Thanks for your answers my friends :-) Tom

          I know a buddy who used to race this same model bike and with a little tuning he said it was not a problem to lift the front wheel off of corners in second gear when gran prix racing. I can lighten it up quite a bit by removing the center stand, kickstand turn signals and replacing the VERY heavy stock exhaust with a vance and hines four into one.

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            #6
            I have been trying to sell it, but no takers. I have already rebuilt the transmissiona and replaced several other parts with new. Front forks are rebuilt. My plan it to freshen the engine, lighten it and have some fun with it at track days here in Portland. Not much demand for an old 550 although in 1983-86 is was considered a pretty quick bike. :-) Tom

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