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Engine won't rev above 3,000 rps when warm!?

Discussion in 'The Garage' started by dontarantini, Nov 1, 2010.

  1. dontarantini

    dontarantini XS650 Member

    Hey guys,

    I recently took a trip down from New Jersey to Florida on my 1980 XS650 Special, during the beginning of the trip I was having trouble with my turn signals, neutral light, & horn not working (all of which are powered by the same fuse), when I shook around the fuse under the box they would start working again (no fuses blown).
    Somewhere halfway through the trip I would put the turn signal on and the engine would cut out whenever the signal would blink, so I stopped using the signals.. a while after that I started noticing that in 1st gear the bike would refuse going over 3,000 rpms, I'd shift to 2nd gear and it would make it through. Little while later trouble in 1st AND 2nd.. then it was just completely stuck at 3,000 rpms (I could go about 30 mph in 5th gear tho! :thumbsup:) Stuck.. I took apart the carbs and cleaned them out, checked fuses, looked inside the headlight for shorted wires, looked inside the turn signal switch. Nothing helped.

    Stuck somewhere in Virginia I camped out for the night, when I get up the next morning I checked the Valves (which I adjusted before I left) and they were fine. I started it up and was surprised to find that it was working, I took to the road again hoping the mysterious problem had gone away.. about an hour or so later it came back. Stuck somewhere in North Carolina now somebody stops by to help, we head over to a bike mechanic he knows and we look at EVERYTHING, we checked the fuel filter, the gas inside the carbs, removed the rotor, checked plugs, swapped ignition coil, checked turn signal wiring and could find nothing.. absolutely nothing.

    He comes back the next morning and we start to try again, he gives the battery a charge (charged for 15 minutes maybe?) with an expensive bike charger and the bike is working again (which it does when cold). I head out again and decide that if its the battery I should keep up high rpms to make sure it stays charged, I hit the highway and it pretty much worked fine til I hit Florida, near the end of Florida it was acting up again with the 1st gear rpm limit but thankfully I made it to where I was goin.

    Now I'm home so I've got a bit more time and not such a rush but am still puzzled as to what it can be, I took my battery to Autozone and had them test it there, they said it was bad so I bought a new battery.. but the problem still hasn't gone away.

    Anybody know what could possibly be causing this? I changed the Rotor before leaving and the resistance is still good, the Stator resistances between white wires seems good and the Pickup resistance as well. The strange part is that the Regulator seems to be charging, it gives me a 14.5 Voltage at the battery when revved up at a standstill. I have no clue anymore.. hopefully its not the TCI box because I can imagine that will be expensive.
    I bought the Chrysler Regulator since the Red wire coming from the original regulator seems to be heating up and starting to melt the connector, I'll put it in tomorrow (I checked the Rectifier and the diodes seem to be intact so I'll just switch the green and brown wires to the new Regulator).
    Btw, where do you guys suggest mounting the chrysler regulator since it needs a good ground?
    If the regulator doesn't work do you guys have any suggestions on what it could be?
    Keep you updated on whether its fixed or not.

    Any help is better than none,
  2. I was guessing electrical while reading and I guess you are looking in that direction. Where in Fla are you at now?

    You might want to look into a short in the harness. Check in the headlight bucket too. Tats where most wires go to and lots of connectors there to get lose. Might be charging fine when still. Running brings out the short and kills the voltage. Try checking batt volts when it acts up again before you put a charger on it or start it.
  3. dontarantini

    dontarantini XS650 Member

    I'm staying over in the Cape Coral area, near Fort Myers.
    I imagined it could be a short but can't imagine where or why it would cause the bike to be limited to 3,000 rpms.
    I checked behind the headlight and didn't see anything too horrible but I will recheck tomorrow incase anything had changed on the remainder of the trip.

    The part that gets me is that I'm unable to understand why it will idle fine but be unable to raise rpms.. is it low ignition coil voltage that can't keep up to the increased demand for spark? Caused by a low battery caused by a voltage regulator or possibly a short in the system that is draining the battery?
    I assume the symptoms could also be caused by a malfunction in the electronic ignition's timing advance (TCI Unit), but I hope not.
    If I get the rpms up they will stay up without a problem, but stop and go at lights for a bit and I'm screwed.
  4. I am across the state a few hours or less. If you head back this way across alligator alley let me know. I have a shed full of XS parts and could probably find the swap out parts to do some troubleshooting for you.

    I would look for low voltage at the batt when it acts up. Maybe rig up a digital voltmeter strapped to your tank while you ride. See what happens when it acts up, 3000rpms? Tap the voltage from the point closest to the ign box.
  5. kvanderploeg

    kvanderploeg The Dutch Terror

  6. dontarantini

    dontarantini XS650 Member

    Thats a good idea TwoJugs, I'm gonna strap a voltmeter to the tank for my ride after swapping the regulator and see what happens. And I'll let you know if I head that way, I might be heading over to Miami within a couple of weeks.

    Very nice writeup Kent, I didn't even want to look at that box wrong due to the fear of an expensive replacement, no idea it could be taken apart like that. I'll certainly be taking that one out tomorrow and see how it looks inside.
    Were you having any trouble with the turn signals or only the neutral light? I'm pretty sure the neutral light and turn signals are getting power from the same place so it could be the same problem.

    I'll let you guys know how it works out tomorrow,
    Hopefully I'll get it runnin right without too much emptyin of the pockets
  7. XSLeo

    XSLeo XS650 Guru

    Well lets stop and think about things a bit. Hmmm, The bikes an 80, so all the parts are at least 30 years old. Your TCI box is at an age where things can start to go bad. Several people have found bad solder joints in the box, loose wires, burnt parts. I might start by pulling the TCI box and looking for anything real obvious.
    Good luck on the fix.
    Just had a thought, is the fuse box still original, if so that may be the trouble. The clips that hold the fuse get weak and can even break off. Replacing them with inline blade type fuse holders fixes lots of problems.
    Last edited: Nov 1, 2010
  8. Travis

    Travis Staff Member Staff Member

    TCI boxes don't cost that much. Lots of people are removing them for Pamco or Boyer units so they are out there. They show up on ebay every now and then. A local bike salvage yard gets about $70 for them. There's got to be a few people here that have them laying around that would probably sell one to you. You could also buy a Pamco.
  9. kvanderploeg

    kvanderploeg The Dutch Terror

    xjwmx, the original poster had problems with the neutral light, but my neutral and turn signal lights were all working fine. Also, his TCI box looked a lot different inside than mine, so there may be differences in the years or even suppliers. Good luck, and keep us posted.

  10. Sounds like a voltage supply issue. A poke around the headlight bucket, harness and fusebox might be worth the time. When it came time to make my harness from scratch I found out that the bike uses the run-stop switch to feed power to the ign system. I expected it to act like a magneto ground to shut the motor off when needed. Since it supplies voltage to the ign it brings new issues to the game. Even if the box gutts show something burnt and repairable I would want to know why it happened? Directionals and horns use a fair amount of current to operate. Weak grouynds can act like a weak power feed too
  11. dontarantini

    dontarantini XS650 Member

    Alright.. I took out the ignition box this morning... what a pain that was, had to take out the entire battery housing out :yikes:
    When I took the ignition box apart though it looked like it was in great condition, I tested the diodes and they tested fine, doesn't mean something else couldn't be wrong with it but I rather doubt the problem is there. I took several pictures of the circuit board which I can post if you guys want to see it.

    I hooked up the Chrysler Regulator but left the stock Rectifier hooked up, then connected a Voltmeter to the battery and started it up. It seems to be charging a bit higher now than it was before, its hitting 14.3-5 volts at around 2,000 rpms, it was capping at around 14.7 while riding and when I would stop to idle (1,250 rpms) the battery was actually at 14.2, which seems a bit high, didn't know it could produce that much voltage at idle.

    The turn signal didn't seem to have too much of an affect on the bike this time, so hopefully with a bit more riding the battery will make it to its full charge and take the signal in stride. I'll ride it a bit more and let you guys know how things hold up, but its looking like it could be the voltage regulator that was causing the problem, atleast thats my hope. If the turn signals drain too much and the regulator is not compensating then the battery could get low to the point that it will not have the juice necessary to fire off the amount of sparks needed at higher rpms, even though it will idle. I read somewhere that it takes even more voltage for a spark to cross a gap when under pressure, so even if you get a spark when you remove the plug and hold it against a ground it won't necessarily spark when inside the engine against the compression.

    Thats my Theory.. hopefully it holds up and this phantom problem doesn't haunt me anymore,
    Thanks for all the suggestions, I'll let you all know how it goes! :bike:

    Btw, I was thinking of replacing the fuses with a blade fuse box, anyone know where I can find a decent fuse block? Saw the 1-Fuse Connectors at Walmart for $3 each but was hoping for a one-piece block with 4 slots.
  12. xjwmx

    xjwmx XS650 Guru

    An easier way to get to it and the r-r is to remove the panel in front of the rear tire and set it up on top of the tire. Gives you pretty good access.

    It might be that reseating the tci connector fixed your problem. Or jiggling the wire connections at the board while you had the board out. Doesn't sound like your voltage was low enough to have much effect, to me. But I haven't read this whole thread.

    I've learned a few more things about the tci and will try to update that thread that somebody referred you to, tonight.

    But - if the engine cut out when the signal flashed it sounds like frayed wires somewhere. But the tci seems to work at a lower voltage than the stock flashers will. If you could jiggle the fuses and fix something, you need to really fix the fuses first.
    Last edited: Nov 2, 2010
  13. dontarantini

    dontarantini XS650 Member

    Well, seems the problem isn't as bad anymore with the new regulator, but it is still there.
    With a voltmeter connected I'm reading 14.20V at idle, when I squeeze the brakes the brake light makes that jump down to 13.30V and then slowly make its way down to 12.90, that seems like quite a bit of a drain on the battery there, and it seems like the alternator can't keep up.
    After holding the brakes for a bit if I try to accelerate (while still holding brakes) it'll bog down, having trouble trying to get through 3,000 rpms like usual, but letting the brakes go and having the voltage pick back up it revs fine.
    The turn signal still makes the engine hesitate but its a much smaller hesitation, doesn't really get in the way of riding.
    New battery, regulator and rotor.. wonder what could still be the problem?
    Maybe these lights are just too much of a drain for an older charging system, or maybe the lights are shorting out somewhere.. could it be a Stator going bad?
    Maybe I should just swap the whole freakin charging system for a perm. magnet setup.. :doh:

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