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power problems - jetting question

Discussion in 'XJ Modifications' started by bbacher, May 15, 2006.

  1. bbacher

    bbacher Member

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    My "new" (to me) bike has pod filters and 4-into-1 exhaust installed. I've read here that both those things require a re-jet to keep the bike running right.

    It's hard to start, and requires a lot of choke for quite a while. Even after it warms up, it will die at a stoplight without a bit of choke (like 1/4 to 1/3). It bogs down around 6000 rpm, requiring an upshift to get any more power. It occasionally bogs down at lower rpm, and if you let off the gas at that time it dies immediately. When it does that, a good 1-2 second rev will usually cure it.

    What do these symptoms indicate? I wonder if the PO didn't re-jet the carbs when the pods and exhaust were installed.
     
  2. bbacher

    bbacher Member

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    Another question: Given those two mods (pods and 4-1 exhaust), what is the proper jet size?
     
  3. woot

    woot Active Member

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    I can't answer the jet size question. With the symptoms you list (bogging down) it sounds like you could definately get some benefit from setting the carbs up properly.

    I don't know why, but it seems that alot of bikes that have aftermarket pipes installed by PO have carb problems - POs don't seem to ever jet properly. Just an observation...

    If you want a quick diagnosis - ride the bike below 6500 around the block. Hit the kill switch and cost back into the driveway. Pull the plugs. If they are black you're rich if they are light they are lean.

    You might find a carb cleaning at the same time gives you the best results!

    Cheers,
    woot.
     
  4. singingotter

    singingotter Member

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    Somewhere someone had an excellent chart of jet size increments based on what type of filter and what type of exhaust. It even included pilot jet increments too. It was a very good resource, and it helped me get mine tuned in. I had to buy the Dynojet Stage 1 & 3 kit, which includes an adjustable needle, and instructions for drilling out the slide lift holes. The adjustable needle is required to get the midrange fuel flow correct. The only thing the kit didn't come with was larger pilot jets, which is what I'm investigating now, but won't install until after the coil upgrade. You also need to turn out the idle mixture screws, or it will stall. A Colortune works perfectly for that.

    It seems that the pods/free-flow exhaust/rejetting require the higher performance coils to properly combust the fuel. I've been taking "baby-steps", and feeling the performance bump up each time. You have to be really patient, or have a lot of money to give to your mechanic to finally get it right. I am fortunate that I have a 15 mile drive with varying driving conditions that help get it right. Once I feel it is "to the max" I'll probably give the PO an opportunity to ride her and see if he can tell the difference. (The PO is my brother-in-law, who gave me the bike out of disgust - he didn't know about carb synchronizing!) Just from what I've accomplished so far, I can definitely tell the difference, but has cost me around $650. I love the bike, so money is no object. :wink:
     
  5. srinath

    srinath Member

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    My guess is ... with pipe and pods you're looking at +6-8-10 on mains, and maybe 1 washer under needle. I'd also start out with air screws at 3 turns out and fiddle them to where its good at low rpm.
    Pilots are a last option if you cannot get the 1/8th throttle part (leaving a stop light with a gentle take off) ... 1 size up on those.
    Essentially jets go in increments of 2.5. I'd start with stock + say 15. So if you have 105, do 120. heck, I'd do 125 and work down instead of 120 and up ...
    The prior experience I have with jetting ... gs 500's and eliminator 1000 both ended up right in that 6 to 10 steps up window. of course that is with stock needles only. If it has DJ or other aftermarket needles ... your mains will be drastically different ...
    For example the 122.5 a GS comes with stock will take the needle from a DJ kit and let it run similar to a 145 or so ... In fact DJ supplies 118 and 122 and 128's with it for the 3 stages. Ever heard of dropping 3-4 sizes on mains ... try riding it that way with a stock needle and you'll know ... anyway ... I'd start at the 8-10 steps up mark for mains.
    Cool.
    Srinath.
     

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