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Tuning the 673 baby kat

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    Tuning the 673 baby kat

    So today we got a break in the weather thankfully. I had been running the stock needles even though I have a 4 into 1 (with a straight through baffle) and twin K&N filters. It ran good but seemed to not pull quite as hard as I had envisioned and the plugs looked a little on the lean side although I could not detect any pinging. So, I pulled the bank and swapped out the stock needles with the Dynojet adjustable needles with the clip in the 3rd position. She sputtered slightly at lower revs in the lower half of the throttle and had a slight hesitation or bog when wacking open the throttle. So, back home, yank the rack again, and moved the needle clip up two positions. Back she ran much better. Pulled good and hard up to about 7500/8000 rpm before she seemed to trail off. She will go to redline but the strength of the pull tapers off above 8 grand. Anyway, no more sputter or only very slightly. And no bog when wacking open the throttle. When I got back I pulled the plugs and they look much better but still maybe a tad rich.

    I noticed however that for some reason, the cylinders run leaner to richer from the left to the right as you sit on the bike. I'm not sure what is causing this. I did a bench sync and used my Morgan Tune to sync the carbs about a month ago and haven't run it much since.

    Here's a look at plug numbers 4 and 3 respectively. Plug 4 is black all the way down the porcelain except at the tip. Plug 3 has no black down in the porcelain. These where taken at 1/3 throttle going slightly uphill so under load. I haven't done WOT runs yet but will next good weather day.

    Thoughts on what would cause the engine to run richer as you move from left to right would be appreciated. Yes, I was stupid and shot the pic opposite of how they are installed in the engine.
    1982 GS550M Rebuilt Winter '12 - 550 to 673cc engine conversion.
    1989 Kawasaki ZX-7 Ninja
    2016 Ducati Scrambler Full Throttle

    #2
    Re your mixture variation - valve clearances can affect it, float levels can affect it. A poor 4 : 1 can affect it...resynch to start with.

    Some years back a friend of mine was racing one of these. 4 : 1 pipe and no other mods. i got fed up with his moaning one day and we did a series of runs drilling the slide vacuum holes until it ran clean and responded well.
    Std is I think, 2.8mm. From memory we finished up with 3.15mm.
    Std needles too. Does dynojet require drilling the slides ?

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      #3
      Yes, dynojet drills the slides which was done. The slide holes do not affect the jetting...
      1982 GS550M Rebuilt Winter '12 - 550 to 673cc engine conversion.
      1989 Kawasaki ZX-7 Ninja
      2016 Ducati Scrambler Full Throttle

      Comment


        #4
        Over oiled filters can cause a choke effect and make it rich, filters dont need to be drenched. Ever so lightly spritz them is good enough..just to add some tackiness but not drown them either.
        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.

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          #5
          stepping out of line with a quick get-away can also produce those results!

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            #6
            Chuck, these are paper filters and are unoiled. I will pull all 4 plugs tomorrow and shoot a pics so you cwn see the progession from cyl 1 to cyl 4. Other thoughts or ideas?
            1982 GS550M Rebuilt Winter '12 - 550 to 673cc engine conversion.
            1989 Kawasaki ZX-7 Ninja
            2016 Ducati Scrambler Full Throttle

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