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GSXR Carby Rebuild

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  • GSXR Carby Rebuild

    Over the past several years now, I have been blabbing on about doing some upgrades to the Grandfather of GSXR's my 1100 J.

    As some of you are aware I had the engine rebuild in 2004 after a premature engine explosion on the Reid Hwy rendering the bike almost incapacitated for 6 months.

    It has just seen the better side of 13k, and I decided it about time I began to get acquainted with the bike, become more familiar with its needs, where it is deficient performance wise to begin, and work around some of the other items as we progress through them. My reasons for wanting to upgrade the bike are simple - it is more deserving of my attention and I have always believed these machines to have substantial potential.

    That which has not been tapped by myself personally - I always hear stories about how my bike does this, and his bike does that where 150hp+ is readily available straight off the production line in standard guise. In this instance I am taking a standard bike (not) and upgrading from there to see where infact it takes us, with small steps to begin and at what cost.

    The intitial outlay in 2004 for a complete "engine rebuild" $6,000:00 quote marks for a purpose as we will discover later, with 1st oversize pistons sporting 10:1 forged flat tops, balanced bottom end, good for a clean run through to 11k for such an enormous engine now 21 years old.

    2 months ago, after much deliberation I began by stripping down the standard BST34SS CV Carbies. I say this because in the past I have always leaned toward having professionals take care of my rides, and so felt ackward about making the first steps. With service manual in hand, removed a few screws, undone some carby clips, removed the pods (K n N filters) the carbies were more or less off in 45 minutes. The hardest part was disconnecting the throttle cable from the carbies for complete serviceability.

    By placing the carbies on the bench the first decision was to think about which end to take to pieces first. Top CV Caps, or Float bowls. I went with CV Caps - Intrigued by the complexity of the system itself, under the cap(s) are diaphragms being held in by springs, which holds down a nylon cap less than the size of a 5 cent piece. Under that is the Jet Needle and retaining clips etc. Which all come out of the flat slide - thats the part which moves up and down inside the carby throat itself.

    The jet needles were corroded and warn quite badly, which is never a good sign. The flatslides were burred around the edges, most likely from weathering over the years, and some indication of one of the carbies not fully functioning, perhaps causing stumbling which I had been experiencing in recent months.

    As the Jet Needles were warn, it is fair to say so too would be the Needle Jets (emulsion tubes as some people know them). All the parts were lined up as they came out, so I could follow each of the carbies standings as they were disassembled. The screws etc went into container for ease of accessibility.

    Turning the carbies over now to the float bowls, the first bowl removed, I was astonished to find that the jet sizes used were not Mikuni, nor Factory Pro, or anything actually identifiable at all. Both wayney and myself spent an entire night online trying to assess just what they were and where they came from. To this day, we still do not know, however what we can say is that the main jet sizes were way too small at a mediocre #116.

    Type: BST34SS
    Main Jet: 130
    Main Air Jet: 0.6mm
    Jet Needle
    U.S: 5D29
    U.K: 4D13-3
    Needle Jet
    U.S: P-2
    U.K: O-9

    Mikuni base Main Jet sizes for this model carby and bike start at #130 - so one has to ask, how this happen if a rebuild had been done? Simple - they re - built an engine with disregard the carbies - what then did my money ever purchase if not a complete rebuild which included carbies?

    Moving on, The remaining Pilot screws, idle jets, and and throttle vales sizes were all conducent with book specifications - so I was happy at this point intime, knowing that some fool had fitted incorrect size Main jets out of ignorance.

    Mikuni specify increments of 2.5 in their Main Jet line up, and as their sizes were 115, and not 116 the next specified size should have been 117.5, which is still a far cry from the standard size of #130.

    From 0 to 160kmh the bike always pulled very well, the best range for the bike under normal riding conditions pre carby strip was around 5-7G. however fell dramatically short of torque pulling power once 180 and onwards was called upon. The power was slow on delivery and seemed to take for ever to reach 220kmh at 9k, seen only once or twice by this jockey since the rebuild in 2004. Needless to say, it spent most of its life under 200.

    After much calling around locally and being told, the bikes too old for anything in terms of power upgrades - cannot get them (bullshit), I finally placed an order with Serco in Queensland for the Dynojet stage 3 jetting kit through Witch Cycles. Regretfully they did not come with new emulsion tubes (only supplied with the Factory Pro Kit through Mick Hone Sydney) and so a separate purchase for new emulsion tubes were made at the dealers.

    Under standing how a carburettor works...................

    Through my own discovery, and comments made from others you understand bikes the term "Black Art" seems to have become a common phrase where carbies are concerned. Finding someone in this day and age pre fuel injection that understands them is becoming few and far between. It takes quite a deal of time to set up a set of carbies correctly as realised by this little black duck, and so I would like to share this with you.

    Throttle positions of the carby engage or disengage different fueling and air circuits of the unit itself. The diagram inserted clearly shows the full operation of each of these circuits and how they affect your bikes performance -

    The typical Dynojet kit comes looking like this -

    With K n N Pod Filters same as these (purchases separately $190+ gst)

    These are the instructions which accompany the dynojet stage 3 kit - fairly straight forward in its explanation to say the least.

    Various options are available in Main jet sizing along with drill bits for resizing flatslide vacuum hole and air screw

    Once an appropriate selection of main jet has been made, install the jets.

    With the Jet Needles as with all carby parts, you must give consideration to all pieces being cleaned before re-assembly takes place. Any foreign matter will foul the operation of the individual units and cause eternal grief to you.

    You will note that the air/fuel mixture screws are preset to a base benchmark before the carbies are re-installed on the bike - this naturally gives you a tried and tested starting point and knopwledge that all carburettors begin operation equally, and not as set by the factory of manufacturer, in this case Suzuki.

    Once you have carefully re-assembled the carbs, making sure all of the instructions have been complied to, re-install the unit(s) back onto the bike.

    When you have done this, it is time to perhaps start the bike and get some fuel flowing through them. It may be necessary to increase your preset idle screw (large dial knob in carby photo protruding downwards) to around 1500-2000rpm, so the bike gets a good shot of fuel flowing in the initial stages - if you have a vacuum fuelcock, you will have to "prime" the carbies first for a few minutes.

    Once the bike has a good shot of fuel, and the float bowls are full, you can shut the bike off and reach for the Carburettor synchronisation Guage. Yes, you will need to run through this process regardless of what anyone else tells you.

    In my case, I give Kudos to HPM for allowing me to use (in his absence) his specially imported gauges for my personal use (cheers buddy).

    It goes without saying that you must have the appropriate carburettor adaptors attached to the individual carbies to perform this exercise; I pre-empted this and purchase factory adaptors from Suzuki for $37.80 for 4 adaptors.

    AS there is no one carburettor on this model which is a designated "benchmark" you must balance the carbies starting with the #1 first. There are three (3) adjuting screws on this model, you adjust #1 first, then #4, and they inturn balance out both #2 and #3 respectively. Once this is done, you undo the locking nut on the centre adjuster and adjust banks 1 and 2 to match.

    Carefully noting that all four carburettors must be within 2cm / hg of each other at around 1750/2000rpm. Take a good look at the carbtune gauges above - the increments are very precise, no room for error there.

    When making these adjustments I found it necessary to perform it a few times in an effort to get an accurate reading across all four carbies, as hot air temperature effects the readings. The bike must be allowed to cool down if you do not have a BIG ASS fan keeping an air/oil cooled bike under temperature control.
    Once you have set your carbies up as best you can, you start the bike returning the idle screw back to 1,000 / 1,200 rpm.

    At this point, you will find it necessary to check throttle response by revving bike to certain intervals (around 6,000rpm and letting it drop back to idle. To rich and it will stumble and stall, to lean could point toward float bowls being inadequate - wrong float levels.

    A thread that I have found interesting in helping set up the carbies, is strangely enough the factory pro website:Factory Pro: Producers of the EC997 Low Inertia Eddy Current Dynamometer Series and Quality MC performance products

    A very helpful site indeed to aid and assist the person wishing to fulfill this task. A Step by step process so you get it right first time !!

    Be careful though, one of the items mentions; - " if the throttle hangs after revving, its because the carbies are running lean " - this happened to me and it was nothing more than a sticky throttle cable - a new one was ordered.

    Once i decided the bike was ready for a road test, I refreshed the tank with new fuel, and began a slow ride taking particular notes of what is happening while I am riding. It was encouraging to note the engine response was hightened greatly, less throttle roll for improved acceleration from 1000rpm upwards right through the rev range was a most rewarding feeling.

    Very satisfied with this indication that I was on the right track, more low speed work was necessary to discover some unusal idle issues, with were smoothed out with idle / air mixture screws. Although the bench mark setting was 2 1/4 by dynajet, I found it essential to play with each of the carbies individually - by turning the screws inward would richen the mixture, it would cause the motor to stumble, at that point turning the screw counterclockwise until it found the best idle point. I had to make the necessary changes to each of the carbies accordingly.

    As the initial setup requires you to place the circlip on the third setting (dead centre ) of the Jet Needle, once it is determined weather or not the bike is running rich or lean, these clips can be moved up (for more lean) or down (for more rich) to suit the individual barrel in question hence a tailor made situation at every turn.

    The best way to find out what each cylinder needs is to ride the bike for a couple of kms and then, pull a plug - decide there and then if the bike is one or the other, and adjust individually.

    It is a long time consuming process, but when its right, its really right. And the best thing is, that you have done it yourself, and feel good about it too.

    To date I am very satisfied with the eventual outcome. Bear in mind that each bike will be different in its setup procedure, this I felt is a good start for anyone looking to improve an older bike like mine.....

    In conclusion; The bike pulls much harder through the rev range in each and every gear - from 100 to 200kmh, it is at its strongest delivering masses of torque in my opinion. Low down torque in first gear has changed by perhaps a 5-6 % margin over standard, but the remaining power is quite substantial - it is my gestimate that the overall power improvement purely in how the fuel is delivered to the system has jumped by as much as 10 to 15%.

    On Sunday past, I had the ocassion to take a ride through Serpentine Dam. On the South West Highway, a full throttle test was performed (with a full tank of gas) pitted against a CBR1000RR 2007 blade. A rolling start from 100kmh in second gear, redlining every shift to 10,5000rpm, whilst the Blade and myself were neck and neck to commence, the 1100J seemed to pull three bikes lengths in third gear and maintained the distance through to fifth gear at 9,200rpm - clean through out the gear shifts and rev range to 255kmh. At this point we both backed off as we were fast running out of straight road. This is one very happy camper people. A 21 year old bike matching a more modern lighter counterpart less than 3 years old - I was impressed.

    From 5,000rpm the bike appeared to pull like a freight train continuously through to 10,500rpm - the redline on this model.

    Where as before the power began to die off from 180+ it was actually pulling harder, more so in fourth gear surprisingly so much so that the fifth gear roll on from 100kmh continued through to 255kmh (indicated speed) at 9,200rpm without fault - thats only 1,300rpm short of redline in top gear !!

    A standing start also showed plenty of low down grunt as compared with standard trim, with the bike lifting its front wheel in first gear running standard sprockets both 14 fronts and 46 rear which were renewed a mere 3,000kms ago, not enough with standard gearing for the clean lift to 2nd.

    This outcome is more than i had hoped for, without further modifications at this time. Perhaps with a lesser weighted rider, this would easily be accomplished with little or no effort at all, but I am up around 120kgs, this is a monumental task for any bike with a 1485mm wheel base. As compared to the Haya busa with a similar wheel base, that bike of course delivers 190BHP from the get go and much more advanced wizardry to boot !!

    The Grandfather is far from dead and buried. There is still plenty of fight left in his ancestry -


  • #2
    showing you age there scara.
    Hot air balloons, the gentleman's escape vehicle.


    • #3
      Originally posted by Shogun View Post
      showing you age there scara.
      Hello Turtle


      • #4
        Comprehensive and informative writeup Scara. Thanks for sharing, and congratulations on the results you got.


        • #5
          Very good write up mate !

          May i ask where you are going with your final tune ? big hp , drive-ability through out the entire rev range , or a torque monster ? Reason for asking is having spent heaps of time on old skool suzuki site and playing with the little brother of your bike for years , i have learnt shit loads from that site , may be able to save you some time getting to your " desired tune " Debaser will also !
          In The PSB Garage
          The build/tidy thread


          • #6
            Originally posted by RAVENGSXR View Post
            Very good write up mate !

            May i ask where you are going with your final tune ? big hp , drive-ability through out the entire rev range , or a torque monster ? Reason for asking is having spent heaps of time on old skool suzuki site and playing with the little brother of your bike for years , i have learnt shit loads from that site , may be able to save you some time getting to your " desired tune " Debaser will also !
            Hey Raven GSXR - Haven't considered that just yet matey - am still doing other upgrades on the front end is the next to happen - making an attempt to fit USD forks, Triple clamp, which will need a clip on upgrade and master cylinder too - radial mounts, then rims to 17' with new swingarm off a late model rig - all this as you are aware takes time and spondoolies - when the bike is finished to where I want it, then I may take you up on the offer of info swap - will invite you over for look see if your interested and we can talk about it :smile3:

            Will post up project as it unfolds - on the flip side however, am very willing and interested to sit down and chat about your findings - always open to that


            • #7
              No probs Scaramouche i'll bring a 6 pack , hmm better make that a block , if im talking GSXR's i tend to woffle on a bit !
              In The PSB Garage
              The build/tidy thread


              • #8
                That site can help you with all your tuning way before you get to the dyno. I set mine up as per instructions from senior members on the site and have never looked back. Alpha Sports - Suzuki Motorcycle Parts Catalog go to this site, look at the bearing sizes for your steering stem, then compare them to the front end you are going to use. Then use a bearing cross reference to match the two. or get a new stem machined up. I got a 2003 tl1000r front end to fit in my 88 750 easy with bearings and a bit of grinding and bashing (chicks love this as well)

                I have, two rear ends with 160 section tyres, one for a gsxr 750 the other for a gsxf 750. I have done a lot of mods on my 750 if you need a hand.


                • #9
                  Hi All just cleaned my carby on my 86 GSXR 750. After I had assembled the bike and throttle cables the throttle housing for that the cables attach to snapped from age. Does anyone have a throttle assembly....Need it over the easter weekend. Any help appreciated. Will pay and meet for pick up!!


                  • #10
                    Originally posted by debaser View Post
                    I have done a lot of mods on my 750 if you need a hand.

                    No shit!!! Do you have a build up thread???


                    • #11
                      Congrats on doing the job Scara, and a great writeup.
                      Good outcome all round and much appreciated here.



                      • #12
                        OK. Found it. For anyone else interested:


                        Sorry about the thread hijack, but ya gotta admit debaser's gixer looks the shit!