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Ignition issues.

Discussion in 'XJ Technical Chat' started by Thethirstmutilator, Jun 16, 2025.

  1. Thethirstmutilator

    Thethirstmutilator New Member

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    Alright folks. Kinda at a brick wall here. I've got 2 problems. 1982 maxim 650. It's my dad's bike, he's had it for about 17 years. Doesn't know much about it so I'm trying to work on it with little info. 1st issue. The bike will not start while cranking with the starter button on, the second you LET OFF it will fire. I've seen videos on these things not doing that. Everywhere I look online I can't quite find anything on this specific issue. 2nd issue. I rebuilt the carbs about a year ago, after putting it all back together, I've noticed that has misfires on cylinders 2 and 4. After some testing, it seems that they do still infact fire, but only when given throttle. At idle (around 2000) only 1 and 3 are hot. The exhaust on 2-4 are just warm. I've looked online and it seems to be that I need to synchronize the carbs. If anyone has some experience or info that could help. It would be greatly appreciated.
     
  2. Roast644

    Roast644 Well-Known Member

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    That's a classic symptom of low voltage to the TCI. While cranking, available voltage is dropping below the 10 volts or so required for ignition. As soon as you stop cranking you get brief spark as voltage comes back up and might fire, or usually there's just a pop and no start. Weak battery can cause that, or voltage loss from corrosion at fuses, switches and wire connectors. Jump it with a known good battery (a big car battery is good), then you'll know if you need a replacement battery, or need to start cleaning corrosion. You can also check voltage with a multimeter directly at the TCI module (red/white wire) while cranking and compare that to voltage directly at the battery while cranking.

    The starter will crank fine at 10 volts and it might sound like your battery is good when it isn't.

    The misfire might be plugged choke jets in the bottom of the carb bowls. Is this while it is still warming up and choke is on? Does it run well enough to warm it up and road test? Or plugged pilot circuit, out of adjustment fuel screw, out of synch. Have you read through the carb cleaning and bench synching info here:

    https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/

    Particularly cleaning those tiny choke jets. They can be a bit of a pain the first time through.

    And then there's valve adjustment if you get through all that...
     
  3. Thethirstmutilator

    Thethirstmutilator New Member

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    I suppose I should've mentioned that it has a brand new battery. The starting issue has been there since my father purchased the bike when I was a kid. The issue is that cylinders 2-4 are only firing when throttle is given. It idles around 2200 when cold on just cylinders 1-3. 1-3 isn't enough to keep it idling when warm. It is capable of moving under its own power, and shifting gears. It's just at idle 2-4 shut off. I will begin further research on tuning the carbs, as I most likely didn't tune them correctly when I put them back together.
     
  4. Roast644

    Roast644 Well-Known Member

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    I'd still do the voltage check while cranking even with a new battery. 1 & 3 cylinders are different coils, so the idle and misfire is still likely carb cleaning and tuning.
     
  5. slackard

    slackard Active Member

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    Clean all your connectors and switches on the ignition circuit (red-white wires). Verify battery voltage at coils and at TCI box. As mentioned above, if the voltage drop is too great, no ignition.

    If you clean all your connectors, switches, etc and still dont see battery voltage at the coils and TCI box, its time for the Ignition Circuit Relay Mod. I did a thorough writeup on this mod for my XS850, and your XJ wiring is mostly similar. Happy to lend guidance if you decide to go this route.

    These are pics from my XS850 your xj will be slightly different... (full write up / xs850 thread here)

    I unwrapped the wire harness black tape all the way from the Kill switch splice, back to the fuse box, added a new fuse and 12ga wire from the fuse up to pin 30 on the relay. Not difficult.. Just take your time and be gentle as you unwrap/re-wrap.
    [​IMG]


    Here's the finished mod, just before buttoning everything back up.

    [​IMG]
     
    Roast644 likes this.
  6. Thethirstmutilator

    Thethirstmutilator New Member

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    Alright. Thank you folks. I woulda never guessed where to look for the starting issue. Just followed the red/white to a plug that was corroded. Cleaned that up and it fired right up with finagling it. I also have discovered the true culprit for the carb issue. Cracked intake manifold boots just after the carbs. Not the ones from the airbox. They seem to be sucking in air and disrupting the balance of the air fuel mixture. Rode it around and it didn't stall when warm.
     
  7. slackard

    slackard Active Member

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    If the engine side boots are cracked, a make-shift fix is to clean them extremely throuroughly, then fill the cracks and coat the exterior with RTV gasket maker.. some folks even cut up old bicycle inner-tubes and slide them over like a sock. Short of sourcing new, or good use boots, this is about all you can do.
     
  8. Thethirstmutilator

    Thethirstmutilator New Member

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    The intake manifold boots are original. Extremely cracked. Never really looked at them beforehand and never noticed. But I've also experienced a surge while it idles. When it drops to low idle it surges up to around 5000rpm, sits there for about a second and then slows down. It continues to do this while running. After a little bit more research, I'm going to assume that it's the diaphragms in the carbs that are cracked.
     

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