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    Carb Rejet Question(s)

    Hello everyone;

    Well... I got my MAC 4-1 header on my 82' GS850G and like the way it sounds WITHOUT the baffle. (Some of you may recall, from another post, that I received a used MAC, but CRC2ONLINE took very good care of the problem -- I recommend them -- their customer service is TOP-NOTCH.)

    Anyway, I need to rejet the carbs as it does not have the "get-up-and-go" it had with the stock exhaust and has some backfiring when decellerating. If I accelerate slowly, the bike runs pretty OK and I can hit 80-85 MPH -- but you can hear that it's not running it's best. When I accelerate quickly it runs pretty crappy, bogs down, etc.


    I found the following specs (for my carbs) here on the forum:
    1982 GS850GZ Carb. Specs.
    Idle rpm/min 1050 +- 100 rpm
    Carb. type: Mikuni BS32SS
    I.D. no. 45160*
    Bore size: 32 (1.26)
    Float height 22.4 +- 1.0 (0.88 +- 0.04)
    Fuel Level 5.0 +- 0.5 (0.2 +- 0.02)
    Valve seat 2.0
    Starter jet 32.5
    Pilot screw pre-set (well.....maybe)
    Pilot air jet #180*
    Pilot jet #40
    Jet needle 5D50
    Needle jet X-5
    Pilot outlet 0.7
    By pass 1.0, 0.8, 0.8
    Main air jet 1.7
    Main Jet #115
    Before I remove the carbs to rejet, I'd like to get an idea of which jets need to be replaced and with what size (that way I can purchase them in advance).

    I've been looking at: http://www.pro-flo.com/proflo_carb_p...#Jet%20Needles for jets, but have not idea of which ones I need.

    Can anyone provide some input/advice on what to get and whether the jets at PRO-FLO are good?

    TIA.

    Charles...

    #2
    I would start with a 125 main jet and raise the needle two notches. If your jet needle is not adjustable raise it with 4 washers (shims) from Radio shack. One washer = 1/2 notch. This is only a base start and you will have to do plug chops to determine if you need a smaller/larger main jet or lower/raise the jet needle.
    If you don't know what a plug chop is do a search. I myself have discussed it many times along with many others.

    http://www.denniskirk.com/jsp/produc...Id=41306&mmyId=
    Last edited by chef1366; 05-29-2007, 01:32 PM.
    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.

    Comment


      #3
      Originally posted by chef1366 View Post
      I would start with a 125 main jet
      OK.

      Originally posted by chef1366 View Post
      and raise the needle two notches. If your jet needle is not adjustable raise it with 4 washers (shims) from Radio shack. One washer = 1/2 notch.
      OK -- but what size washers from RS? Can you give me a thickness so I can get them anywhere? Also, I think I read somewhere that the notches on the jet needles were removed after 81', and I've got an 82'. Guess I'll have to open the carbs to see.

      Originally posted by chef1366 View Post
      This is only a base start and you will have to do plug chops to determine if you need a smaller/larger main jet or lower/raise the jet needle.
      If you don't know what a plug chop is do a search.
      I know what one is, but am wondering if I need to do it or would using a colortune tell me?

      and... thanks for the link. Are Kirk's jets better than PRO-FLO

      Comment


        #4
        Dennis Kirk has Mikuni jets which are the same.
        I bought a bag of assorted small washers and there were some that were the same size as the one on the needle.
        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.

        Comment


          #5
          Well... I called DennisKirk.com and spoke with a guy there about re-jetting my bike. He said I need to buy the DynaJet Stage 3 kit for $120 (http://www.denniskirk.com/jsp/produc...ductId=p171808).

          Is this really true? (I think they just want to sell me $120 worth of parts instead of $15).

          Also... do I need to replace other jets such as the 1) Starter jet, 2) Pilot air jet, 3) Pilot jet?

          Could sure use some additional advice.

          TIA.

          Charles...

          Comment


            #6
            The jet kit will "fix" several issues with the stock carbs, like factory-induced leanness to meet emission standards as well as address richening things up for the headers. The kit also has adjustable needles so you can fine tune your setup a tad easier.

            All that said, all you really NEED to do is go with a bigger main jet and raise that needle a bit (or find a different needle that will allow a slightly richer mixture throughout it's travel. Don't bother with the pilot and starter jets, they aren't going to help the problems you originally spoke of.

            Comment


              #7
              Ditto Mark
              With the 4-1 pipe all you really need is a bigger main jet and raise the needle.
              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.

              Comment


                #8
                For just a pipe and totally stock intake, I'd try 7.5 to 10 larger on the mains. That's one and a half to two sizes up.
                For the jet needles, I'd probably try a 1/2 position richer. A typical jetting spacer used for 1/2 position changes, is approx' .022" thick. If you want to try a full position, double that. Solid 1/3 throttle chop tests will tell.
                As for the pilot circuit, maybe a small richer adjustment on the mixture screws will be needed. About 1/2 turn additional?
                You may have to get larger air jets too but try the stock ones and test.
                Don't bother with a stage 3 kit, that's only for pod filters.
                And on the seventh day,after resting from all that he had done,God went for a ride on his GS!
                Upon seeing that it was good, he went out again on his ZX14! But just a little bit faster!

                Comment

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