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Runs like butter until 4.5k rpm then sputters

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  • Runs like butter until 4.5k rpm then sputters

    Last night I purchased an 06 katana 600 after over a year and a half of a ninja 250. I’m really happy about things however there’s some things I need to do before she’s worthy of the next daily title. I bought it cheap and was expecting to work on it anyways, however I feel like I’m going around in circles so far trying to figure this out.

    what I know :
    guy I bought from had put some fair money into it getting it running like factory, full carb clean and tune job (he said he put 1200$ for that &#128565 sold it a month ago to some guy that put on a slip on shorty, halogen light and probably more we don’t even know of. Guy who bought it never registered it to him and fails to run from the police. Put 2k miles on it in around a month after it was refurbished, ends up in jail, possession returns to the guy I bought it from (let’s call him J). J knew it had some new issues and I got to increase CC by 350 for cheap. NOW I have the luxury of getting it to good running condition myself

    why I’m posting this :
    I rode it home (near 2 hours) and was in a very odd state of happy and sad. Bike will run to 4.5k rpm like butter compared to my ninja 250, then it starts feeling like my 250 😂. Almost like it’s running on 3cyl or less, exhaust tone starts sputtering and bike losses power unless I really twist the throttle (still can tell it’s running at maybe half power of what I’m expecting it to while wide open). It will climb and hit limiter (only tested that once.. in 2nd) from what I could tell it doesn’t matter what gear you’re in or how fast you’re going. 4-5k rpm and I’m back on my 250.
    mechanically the bike should be near perfect, I have the air box and tank all off and can tell the carbs are still clean (as clean as you can tell from the intake ports).
    without saying it’s a cylinder down, it feels like it’s not getting fuel, like my 250 when it’s about to run out of gas. My first assumption would be bigger jets in the carb, or needles. Not too well versed in what part does what or their names. J said he has some bigger jets from the katana he had like 6 years ago that are still in packaging (he didn’t want to get into all the carb shit which I fully understand) he’s looking for them currently and will mail them over whenever he finds them. Me being impatient I’m still trying to see or figure out if there’s anything else it could be that I could do to get on the road quicker. Considering the state it’s in I don’t necessarily want to ride it in fear something else goes wrong.
    only other issue I know of is an oil leak on the ignition / signal generator cover, will be ordering that gasket next paycheck, is there any other even preventative maintenance type things I should be ordering or looking at?

    Only thing I’ve done so far is adjust the fuel screw at the bottom of the carbs and that didn’t change anything aside from make the crackles and pops a little beefier. Which in hindsight I’d only really need to adjust those if the entire range is affected but it was worth a shot I think

    just to reiterate, both me (only mechanical experience being diy work on my 92 civic and the 06 ninja) and my grandfather (old man experience) say it’s not getting enough fuel after that 4-5k mark. Carbs ‘should’ be clean and fully functional. Starts up and idles fine

  • #2
    My guess is that the engine is starving for fuel. When rebuilding the carbs, float levels are often set wrong. They are not easy to get right since you basically work on them upside-down. If the floats are set too low, they will cut off the fuel supply early. You may have enough in the bowl to run up to 4500rpm, but then it starts to run lean.

    I'm not a mechanic, but that's my theory.