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Who's good with flatslides?

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  • Who's good with flatslides?

    Running keihin fcr 35 flatslides have been using these carbs for about 4 years, I do the maintenance on them and clean them, set float Heights etc without drama, we run my car on the chassis dyno at work the other week just to see what it is putting down to the tyres as I rebuilt my engine and modified it a bit not long ago. I had the air/fuel wand in the exhaust during the runs, had it set on alky, target a/f ratio for methanol is about 6-1, at idle and low load (cruise) in 2nd and 3rd gears it was real rich (4-1) when I set the ramp on the dyno to load+full throttle to start the run it was leaning out pretty bad (7-1 even 8-1) from 5000rpm wide open throttle 3rd gear all the way up to 14500, after 14500 it started to see nicer numbers around high 6s and at 16900 it was spot on at 6-1.
    This is where I'm a little confused as where to go, in the mikuni book I have it says that at wide open throttle it is running soley on the main jet, if I fatten up the jet will it make me rich up top or can you adjust one of the air bleeds under the velocity stacks to richen mid range up? I thought about raising the needles but that probably wont do anything as it's a condition at wide open throttle and full load, if I drop the needles will that clean up the light load (1/4 throttle 4-5000 running rich) any help would be greatly appreciated (even from you 270 tuning wizards)
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  • #2
    I think larger needle jet. That's the tube the main screws into

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    • #3
      Yeah that crossed my mind, so bigger jet nozzle will richen up wide open throttle at mid rpm range?
      Sean Henderson Racing.. Q73
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      • #4
        www.keihin-na.com/assets/1/7/slide_valve.pdf type in this web address to find your answers. This would be much easier than me trying to explain all of the tuning options.

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        • #5
          Thanks Jim and Brian, I will try to work it out from info given
          Sean Henderson Racing.. Q73
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          • #6
            I would start with a needle with a thinner taper.

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            • #7
              The problem changing the needle taper is ftz make there own needles so how do you know what taper you have

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              • #8
                Well I don't know the origins of the needles I have in it. There the same needles as what came in the carbs when I bought the car in 2011, the guy that had it before me used to get his engines done over in the U.S. At Clifford cycles, either way you guys have pointed me in a direction to go, now if I add more air to the slow air bleed (say half a turn out) then run bigger nozzles that should lean out the mixture down low at light throttle (cruze and idle) and it should richen up my max load/full throttle from 5k to 14k right?
                Sean Henderson Racing.. Q73
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                NQ crash and 4wd spares
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                • #9
                  ok your problem is at wide open throttle but a mid range rpm lean out correct , the needle taper at this point is not a factor try lowering the clips to raise the needles out of the tubes further

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                  • #10
                    Awesome thanks Jim will try that when I get my new cyl head and get it back on the dyno
                    Sean Henderson Racing.. Q73
                    Sponsors..
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                    • #11
                      Aussie have you ran the flatsides set the same way for 4 years and then added CCs to your motor? i wouldn't be afraid to richen up the whole mixture because it's going to need that fuel
                      racing is fun.

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                      • #12
                        Still same cc but I have done extensive port work, modified my pistons and mixed and matched cams and cam timing along with some other little goodies, so yeah I'm not surprised as u said that the fuel mix is out the wIndow, up top at 16900 it's bang on 6:1 wich is what we are after, I might give it just a bit more fuel though for the cold nights
                        Sean Henderson Racing.. Q73
                        Sponsors..
                        NQ crash and 4wd spares
                        Intense lighting systems
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                        • #13
                          Originally posted by AussieQ73 View Post
                          Still same cc but I have done extensive port work, modified my pistons and mixed and matched cams and cam timing along with some other little goodies, so yeah I'm not surprised as u said that the fuel mix is out the wIndow, up top at 16900 it's bang on 6:1 wich is what we are after, I might give it just a bit more fuel though for the cold nights
                          How much of a gearing change are you going to make?
                          I would say you should definitely be prepared for the colder nights
                          What's the ambient temp of the dyno? Should also take that into consideration compared to what it may be at the track and also the difference in elevation or where you stand now compared to where the track sits in regards to sea level
                          racing is fun.

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                          • #14
                            I have put two more teeth on the back of it, the dyno is at sea level, same as track, we have pretty average air quality when we run it on the dyno at work, it's generally 6-10 degrees hotter, from other cars I have run on the dyno for customers we have worked out that we need to go up two jet sizes at the track, .114 jet on the dyno will run a .116 at the track in winter
                            Sean Henderson Racing.. Q73
                            Sponsors..
                            NQ crash and 4wd spares
                            Intense lighting systems
                            Intense racing engines
                            Royal precision lubricants
                            Wayne Leonard Motorcycles
                            Reef Engineering

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