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HELP! Is having a rev limiter necessary? Digital speedometer install.

Discussion in 'XJ Modifications' started by Shabby cube, Jan 6, 2021.

  1. Shabby cube

    Shabby cube Member

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    Hi fellow old bike fetishists!

    So I'm building an XJ 900 1983 scrambler/brat style bike. Currently I am in the process of replacing the original speedo-cluster with a cheap, chineese, digital speedometer/tachometer. When mapping out all the cables I found the cable going from the original cluster going from the "rev/limiter switch" (as Haynes manual describes it). Looking around on the forum I found out that the rev limiter on XJ 900 bikes are switched in by the original tachometer. I'm bummed out and feel like such a noob for not realizing this earlier and I'm now at a crossroad.

    Question 1: Is it entirely necessary to have a rev limiter on this bike as I don't see it likely that I'll ever reach those high RPM's on the bike? (I mean, I might mess up a shift and flick my wrist and destroy the engine... But maybe that unlikely enough to not worry about it :p )

    Question 2: Has anybody encountered this dilemma before and found a good replacement/aftermarket rev limiter or figured out how to incorporate the old cluster's rev limiter into the new state of the bike?



    136142922_870033787131377_4290720886410387445_n.jpg 136103439_857967354966616_4700897749123554740_n.jpg 136114147_1055408941613446_8725707773269607784_n.jpg
    Any help or comment immensely appreciated!!!
     
  2. Minimutly

    Minimutly Well-Known Member

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    Don't worry about it, a shift light is better though!
     
  3. Shabby cube

    Shabby cube Member

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    Not that big of a deal then I guess?
    Don’t feel like I need a shift light tho, exhaust is plenty loud to tell me it’s time to shift :D
     
  4. bensalf

    bensalf Well-Known Member

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    most of the "multi-function" Chinese speedos have a rev limit indicator light ,you can set at the revs you want.
    looks like following the drawing, the rev limiter switch grounds out the t.c.i., dunno if it acts on both coils or just one, but i think i would prefer the indicator light.
    just sayin.
    stu
     
  5. XJ550H

    XJ550H Well-Known Member Premium Member

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    rev limiter is so you do not exceed redline. there are after market tci to eliminate the rev limiter I do not think it is available for your bike. I have seen them for the vstar because they did not come with a tach.
     
  6. Shabby cube

    Shabby cube Member

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    Thanks for the input guys!!!!
    I’m gonna risk it without rev limiter. Too complicated for me to install a vstar tci into this bike... But would love it if somebody found a simple rev limiter installation alternative.
     
  7. Jacob XJ 900

    Jacob XJ 900 New Member

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    Guess you can easily do without the rev limiter.

    Bought an expensive (and very awesome) German speedo & rev. counter 15 years ago. Works perfectly.
    The rev. counter can bee configured so when you meet a specific rev ex. 8.500 revs. per minute - you will have some LEDs to light up. Its not an electronic "motor break" , not connected to the TCI - just a visual signal, but its absolutely bright and clear. Works like a charm.

    I guess yours have the same feature.

    And as others says - you will be able to hear it when your revs come near 8-9000 revs. per minute.

    Good luck.
     
  8. k-moe

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

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    None of the other XJ models of that era had rev limiters.
    As for shifting by the exhaust sound goes....you'll be surprised to find that there is not a discernable difference in the sound between 7k and redline. And there is no change at all above redline. Hook up a shift light. Your engine will thank you.
     
  9. PavelK313

    PavelK313 Active Member

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    As mentioned above, XJs don’t have limiter. I have analog tach and digital speedo on my bike with Max parameter memory and if I remember correctly I over revved my engine to 12xxx rpm (wasn’t intentional) without issues so far.
     
  10. k-moe

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

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    The XJ900 does. The TCI cuts spark when redline is exceeded.
     
  11. Franz

    Franz Well-Known Member

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    Yes the Yellow wire with the black stripe if my memory serves me correctly.
     
  12. Shabby cube

    Shabby cube Member

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    Thanks guys! Really helpful!
    Found out something else about the bike tho....
    I have most likely been riding it for a season without knowing it was only running on 3 cylinders.... I even synchronized it lol.....
    Opening another thread about it
     
  13. Shabby cube

    Shabby cube Member

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    Hi!

    Sylinder number one on my XJ 900 1983 31A wont run (header doesn't get hot like the other ones) and I have probably ridden my bike for about a season with only 3 cylinders firing (guy who sold it to me didn't inform me so he probably did too for a few years....). I bet it's a new record of dumb dumbness..
    AAAAnyways, the spark plug in number one is carbon fouled, the other sparks are fine. I tried switching plugs, didn't help. I tried switching sparkplugs leads, nothing. I did a compression test, cylinder 1-3 are all on 134 psi and cylinder 4 is at 150 psi. I did a carb clean a few months ago, but I dould have missed something. Rejetted it (bought "stage 2" jets on ebay sinse bike has pereiod-correct aftermarket exhaust, and it wouldn't run without choke before, it does now, on 3 cylinders..)

    1. Can a choke malfunction, mixture screw adjustment, other carb stuff cause a cylinder to not make header pipe hot like the others?
    2. Since I "synchronized" the carbs with only 3 cylinders running, could I have adjusted them so bad that one cylinder isn't getting any fuel at all? or just way to much?
    3. Are there small passageways where air travels in carburator that might be blocked?
    4. Could something in the carb not allow fuel to pass? (I even sprayed starter fluid directly into carb number one while engine was running and good plug was in cylinder, nothing...)
    5. Could one of the cylinder header pipes be blocked, mice?

    Any help would be extraordinarily apreciated!!!!!!!
     
  14. Huntchuks

    Huntchuks Well-Known Member

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    Check spark in #1, could be bad cap, wire or coil. You can also swap wires of cylinder 1 and 4 since they both fire at the same time. If all is well, time to progress to step 2.
     
  15. Shabby cube

    Shabby cube Member

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    already tried, cylinder still dead
     
  16. Toomanybikes

    Toomanybikes Well-Known Member

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    Did you forget the rag you stuffed in the intake when you had the carbs off?
     
  17. Franz

    Franz Well-Known Member

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    Is there any damage at
    A ruptured diaphram on the slide on the dead cylinder would have the same effect, choking the airflow as the slide would not rise. Surely the compression figures would rule the rag left and ruptured diaphram as causes.
     
    Last edited: Feb 15, 2021
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  18. Franz

    Franz Well-Known Member

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    What you haven't mentioned are your valve clearences. Check they are all in specification before working on your carburettors.
     
    Last edited: Feb 15, 2021
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  19. k-moe

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

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    Did you clean the carbs, or did you refurbish the carbs?
    Just a cleaning won't do.
    The rack should have been broken, and every part removed from the carb bodies for cleaning, inspection, and replacement of the old rubber parts. Then the float heights set, and the carbs synchronized.

    My bet is that you missed something.

    IN THE CHURCH OF CLEAN
     
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  20. k-moe

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

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    Merging threads.
    One per bike. More than one makes it easy to miss things.
    I can rename the thread for you if you'd like.
     

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