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Fall tuning?

Discussion in 'XJ Technical Chat' started by bill, Oct 8, 2008.

  1. bill

    bill Active Member

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    OK folks my plugs were a fairly nice brown, I was working towards perfection with small tweaks. Bike running great.

    Now I have a light tan - a noticeably leaner mix. Bike still idles and runs great.

    There has been some discussion about cooler weather, more oxygen etc making the bike run better.

    So does the cooler weather lean the mixture slightly? Nothing else has changed and I doubt I developed a sudden air leak.
     
  2. tommyrhodes

    tommyrhodes Member

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    is it really that much cooler in NC already?
     
  3. Zookie400

    Zookie400 Active Member

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    YES! i live in CT, our weather DROPPED (feels like we skipped fall) and i had a light tan (almost too lean) and when it got cold i developed a stumble at low rpms. gave the screws another 1/4 turn out, back to a nice tan color and no stumble.

    the cool dense air definatly has an effect on jetting. for the next race this weekend i will be going from 175 main to 178, strictly compensating for temps.

    if you are not terribly lean to begin with, you probably are not going to need a rejet.
     
  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    I was going to start a thread about plug reading but this one will do...Bill, when you check your plugs, are you doing "plug chops?" Or just pulling them and having a look after a typical ride, as long as you didn't do so much low-speed riding at the end to throw it off? I'm asking because I have never been able to reconcile the WOT plug chop with the fact that my bikes (and many others I'm sure) spend VERY LITTLE time at WIDE OPEN throttle. I pull the plugs and look at them periodically, isn't that more of a real-world indicator than running wide open and then doing a "read?" Oh, and yes, it got down right nipply here in MI over the last two weeks.
     
  5. bill

    bill Active Member

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    When I got close to my best tune it was 70 in the mornings and 80s in the afternoon. Last week has been 50 to 55 in the morning and low 70s in the afternoon. I have plenty of adjustment so I don;t see the need for rejet but it appears I'll have to do fall and spring tunes.

    Fitz I have used 5k chops with a fan but I found they seem to set me too rich when I ride normally, even though I had a nice tan/brown when choping. I have been checking them once or twice a week (unless I have been tuning then more) after riding. My street is 1/4 mile so I come down it in 2nd at about 4k or so and kill it in the driveway then pull the plugs.

    I think the WOT reads give you an indication of the mix over the entire RPM range? But I have been having success with just reading the normal ride plugs so unless I learn more reasons to do the WOT I'm OK with what I have been doing.
     
  6. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    That was my thinking too. Had a 50-mile all backroads errand yesterday and made a real attempt to "inventory" how much I actually go WOT. Almost never, even with the 550 it revs so quick I really never need to screw it all the way on. Even on the freeway running 80 with rush-hour traffic it's never against the peg. I'm sticking to "real-world" readings too. Now then, another thought: With YICS operating normally you're reading not only the output of the carb on the cylinder you're checking, but also a combination of intake charge from at least two of the other three cylinders. Since we don't ride with the YICS tool engaged, what we see is not a "pure" result from cylinder to cylinder. I think that's one reason fine-tuning the carbs is such a black art. Any adjustment made to one carb affects the other three through YICS.
     

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