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radian 600 Powerband question

Discussion in 'XJ Technical Chat' started by Jake750, Mar 17, 2021.

  1. Jake750

    Jake750 Member

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    So the weather is starting to warm up here in the exotic land of Michigan and ive actually been able to ride my Radian 600. One thing I noticed is that the powerband is quite flat from idle until around 3 or 4 thousand rpms. It's not like it wont rev unless the clutch is pulled in but it feels as if the first 4 thousand rpms are kind of useless. I feel like I have a carb issue but this is my first (running) pre-2000 inline four 600cc so I dont really know for sure. Basically what I'm asking is whether or not this is a normal powerband for this bike.

    I recently cleaned the carbs and changed both sets of carb boots. Also had a recent valve adjustment and can confirm they are within spec. Carbs were supposedly bench synced by the PO before he sold it to me. Looking for some advice before I pull the carbs off again.

    Thanks in advance, guys.
     
  2. Simmy

    Simmy Well-Known Member

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    The notion that the PO bench synced the carbs is meaningless. A recent valve adjustment also makes any previous sync mute.
    A bench sync should sync your carbs but they need to be matched to the motor.
    If all cylinder's valves are opening precisely the same lift (and piston rings sealing all the same) then a bench sync should theoretically balance all cylinders.
    In practice, each cylinder's inlet valve is set within a tolerance, the rings may seal a little different, imperfections in the cylinder wall, all these differences are made up by adjusting the carb sync screws with the motor running, or a vacuum sync.

    I have an FZ600, essentially the same set up as the Radian. There isn't much low down torque with these things.
     
    Last edited: Mar 17, 2021
  3. Jake750

    Jake750 Member

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    Thanks, Simmy. I'm going to try and find a shop that does carb syncing. Does your FZ's powerband match what I described above? Also, at what rpm does the powerband on your fz become "usable"?
     
  4. Simmy

    Simmy Well-Known Member

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    @Jake750 I love your term "usable" LOL.
    My FZ needs revs to get going for sure, probably like your Radian there isn't much happening until you get above 5,000.
    After 7,000 it pulls hard, that's when it gets very usable.

    There is lot's of explanation here on the forum on doing the sync yourself.
    Some have made their own manometers with glass jars and aquarium tubing.
    I like the 4 strip Motion Pro stick myself, essentially 1 hour of shop labour will buy this gadget anyway.
    Then you're all set after your next valve adjustment.
     
  5. Jake750

    Jake750 Member

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    My brain dosnt usually turn on until after lunch. Sometimes later. Let me try again. Under 5000 the power feels like someone tied an anchor to a physically handicapped turtle. Over 6500 it takes off like that time I took my dog to the beach and a crab locked on to his K9 fur cashews.
     
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  6. Simmy

    Simmy Well-Known Member

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    Let me put it this way, if I'm cruising in 6th gear at 3,000 and whack it open, it will carburate cleanly but the acceleration is not good.
    You need to be on the shifter with these things.
     
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  7. Kickaha

    Kickaha Active Member Premium Member

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    At 3000 rpm and whacking it open you really need to change down a couple of gears, they need double that to really start working
     
  8. Minimutly

    Minimutly Well-Known Member

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    Carb synch won't improve your power band, open throttle is open throttle. Maybe check you have the right tci? Fuel levels good in all carbs?
     
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  9. Jake750

    Jake750 Member

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    My daily rider is an fz-07. I think its torque spoiled me, it's torquey from idle to redline. Going from that to my radian 600 felt weird as there is a big flat spot until about 5000.
     
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  10. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    If it's in proper tune that isn't a flat spot, it's just how things were back then. You were spoiled by that short-stroke liquid-cooled engine.
     
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  11. a100man

    a100man Well-Known Member

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    I concur with the above - Radian powered XJ550..
     
  12. Yammaat

    Yammaat Active Member

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    The smaller the engine the more you need to shift.
    My V65 Magna with dynokit, cams etc pulled the cobblestones out of the street at almost any rpm.
    Pulled, just on idle, 2 persons in 4th gear... Wheelied in 4th gear at 100 mph I found out by accident..lol
    My Seca doesn't do that's for sure. It's just another way of riding motorcycle.
     
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  13. Jake750

    Jake750 Member

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    Thanks for the input, guys! Good to know that's just how it is. Hard to appreciate the engine when you're wondering if something is wrong the whole time.

    Since I have you all here, what do you guys like to set your idle at? Can't seem to figure out a good idle rpm.
     
  14. Yammaat

    Yammaat Active Member

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    Yes, as the engine warms up the mixture gets more explosive.. hence more rpm.
     
  15. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Since the 550 has a hydraulic primary chain tensioner it's recomended that idle be set at 1500 RPM, ortherwise the tensioner can be a bit too slack.
    Set idle after you've gone on a ride to make sure the engine is fully at operating temperature.
    You may have to adjust it a few times to find the sweet spot between having a good idle when hot and being able to start it when cold.
     
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  16. Jake750

    Jake750 Member

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    whoa that seems high. i was playing with between 800 to 1000. No wonder it didnt feel right.
     
  17. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    1100 is the recommended setting from the factory, but that can make the aforementioned tensioner too slack in most cases.
     
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  18. Jake750

    Jake750 Member

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    Turns out the exhaust manifold nuts on the #3 cylinder exhaust was very loose and wasnt sealing at all. I had noticed smoke coming out of the front end when it was dark out but told myself it was just some oil burning off from when I replaced the clutch. The two exhaust nuts came out and fell off at some point and I didn't know what the hell was going on until I noticed the #3 exhaust pipe was fully disconnected from the exhaust port.

    Probably explains my idle always felt so rough. Probably also why the powerband felt irregular. When removing and reinstalling the exhaust, remember to always double check your..... nuts.
     
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  19. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    There's no probably about it.

    I had two exhaust manifold nuts back off during a long trip (during the last day riding home). It was obvious that things were wrong, but not obvious as to why until I got home.
     

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