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Follup up on upper-RPM hesitation (m)

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  • Follup up on upper-RPM hesitation (m)

    About a month ago I notice a hesitation around 6-7k when I would go WOT. I, with the support of others on the site, deduced it was either fuel or spark. Since the plugs were due to be changed anyway, I ran through a couple tankfuls of Chevron Techron to clean the fuel system out. Almost immediately I felt a slight difference - but continued to get the hesitation previously described.

    So today I changed the plugs - really quite easy to do. I pulled the battery and let that charge up and cleaned and re-oiled my K&N air filter while I did the plugs.

    Upon pulling the air filter, I noticed something. At the beginning of the winter, I was getting some stumbling when I got on the throttle. I noticed that the restrictor donut had been sucked into the air filter and was bouncing around - thus causing the stumbling when the demand for air became great. So, I pulled the donut out and reinserted it. Since it was cold and getting dark, I really didn't pay much attention to the donut itself and inserted it from the seat side. Well, today, after disassembling this area, I pulled the donut out again....and noticed that I basically had it in backwards. It is supposed to be mounted from the filter side. There is a slight venturi shape to the center going in one way and a hard edge on the back. I had the hard edge facing the incoming air charge!!! This would totally explain the hesitation I was feeling when I went WOT!

    Soooo...I have basically done a nice Spring tune up! The new plugs are in (gapped correctly right out of the box). Air filter is cleaned, donut is now in correctly, head bolts re-torqued, fuel system CLEAN. Oil change and chain lube and I'll be good to go!

    Some things I noticed upon pulling the old plugs:
    1) She's running very well. Excellent coloring on ALL the plugs.
    2) 3 of the 4 plugs were now gapped at .028-.029" (I'm guessing due to electrode 'erosion') but the 4th one was below .020" . Almost like it was dropped before installation and never re-gapped.
    3) They were all very loosely installed - barely (if at all) beyond hand tight. I don't know if they loosened up or they just weren't torqued down correctly...regardless, they're in correctly now!

    I just wanted to follow up on this an hope that me being an idiot could possibly save someone else some time and/or aggravation.

    Thanks to all! You guys give me the confidence and support to tackle these little jobs - safe in the knowledge that I can always come on here and ask if I really screw something up or get stuck or need direction.
    '95 Suzuki GSXF Katana 600

  • #2
    Glad to hear that it's resolved. I would have never guessed the K&N donut...

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