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Carb tuning question

Discussion in 'XJ Modifications' started by willierides, Jun 29, 2007.

  1. willierides

    willierides Member

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    Okay, I'll try to make this short. I have been putzing with this bike (1981 Maxim XJ650) for three years now and am ready to put it on the road once I get some new turn signals for the rear (tomorrow they should get here...) that will pass inspection.

    When I bought the bike it had the stock air box, but it was cracked and HAD NO FILTER in it! So, I went with individual wire mesh type, pods or whatever you'd call them. I re-jetted the carbs per the dyno jet recommendations....41 on the PJ, 118 on the main, up from a 40 and a 110 respectively. I have a four-into-one RC Engineering pipe on it. I did NOT touch the air screw (or fuel? Can't remember which it is on the Maxim). Well, it was hell to start and ran like crap. I decided that since it seemed to start and run decently with the stock air box and no filter element that I'd throw the stock jets back in. I did put the 110 mains back in, but left the 41's in the pilots thinking it can't make THAT much difference. Well, it starts a little easier, but is still really hard to keep running until it revs up a bit on it's own. Once it's warmed up it runs pretty good and starts right up every time, until it cools down. When it's running it still spits and pops a little back through the filters and if I crack the throttle there's a very noticeable bog or miss. The throttle doesn't seem to hang much once it's running. It hung badly when I had the 118's in there. I have not pulled the plugs yet. I think I am going to try to adjust the air/fuel screws, but am not sure which way yet. I plan on studying the manual and trying to come up with a diagnosis and trying a solution, just not sure what I'll come up with.

    Does anyone have any suggestions or ideas? I live in upstate NY, normal summer temps here (anywhere from 60 - 90 degrees) and probably a couple to a few hundred feet above sea level.

    Here's a pic taken before it was actually done as far as it is now. I've made a few changes since this was taken:

    [​IMG]

    [​IMG]
     
  2. RickCoMatic

    RickCoMatic Well-Known Member

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    The Stock Jetting can't handle the overabundance of air in the Air-Fuel Ratio when the Airbox is abandoned for Pods.

    Can't do it! Too much Air happening! You're LEAN. No too ways about it.

    The Jet Kit had you on the right track for getting the Air-Fuel Ratio back toward where MORE Fuel got added to try and bring the A/F Ratio "better."

    You should put the Jet Kit right-back in the bike and Adjust the Idle Mixture as Rich as the bike will tolerate without stalling.

    The XJ-Series Engines are dependent on restrictive Air Intake through the Airbox shared by all 4 Carbs.

    Once the Airbox is substituted for Non-restrictive Air Pods ... You start playing a Motorcycle Tune-Up Game called:

    "Fugg-with and Tweak the XJ with no Airbox."

    The Game gets-old ... Fast!

    Because ...

    No matter if you just had the last move ...
    It's ALWAYS your turn!

    [Hey, Willie ... UpState, near Saratoga Springs. That's my hometown.
    One other thing ... If that's a Union Snowman ... you're paying Double-time and a-half this time of year!]
     
  3. regulator

    regulator Member

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    I have re uilt my carbs a number of times, with only minnor adjustments need (after the first two times LOL). I have also rejetted them for pods and straight exhaust pipes per the dynojet 3rd stage kit. If you have free flow exhaust and pods you want to use the stage three set up, if only using pods OR free flow exhaust you want to use the stage 2 set up. What I have found to be the easiest way to synch them (for me any how) is this: I cut the top off of a 2 liter soda bottle, and a petcock and fuel line in the bottom and added a hanger to the top, this way I can leave the tank off and run fuel from the bottle (hanging it off the handle bar) this makes it easier to adjust idle and pilot jets. I set the pilot jets at 2 turns from bottoming out. Then idle the throttle to 2,000 rpm's then one at a time turn the pilot on the carb down til you hear the cylinder drop (not firing) slowly turn back out until the cyclinder picks back up, and give a 1/4 turn more. This has seemed to work very well for several bikes I have done carb work on. If you have one I also use a temp gun (laser pointer style), to check the heat of the individual headers. I let the motor cool down after setting carbs, fire the bike up and then check the header temps, I have found if all cylinders are firing well the heat output should be very close (within about 5-10 degrees) to each other, if they are not close one of the cylinders is misfiring and should adjust the carb. I may get lucky alot LOL but this method has worked time after time and on many different kinds of cycles.
     

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