Another old bike out of the boneyard - TX750

Discussion in 'Old's Cool' started by SOS, Oct 26, 2011.

  1. SOS

    SOS Ignorance is a gift

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    I found an old, ratty and rusty TX750 in a motorcycle junk yard last Fall. It had a cool looking motor and the early Yamaha alloy rims that I wanted for an XS650 street tracker project that I keep threatening to do. It also had good fork tubes (also for the XS650).

    Someone had done a sort of Brat / Bobber treatment to it in the past and I liked the yard-art look so I bought it and stuck it in the shop window. I figured I'd tear it down for the wheels, forks and swing arm and scrap the rest when I started the XS650 street tracker. Well, things were slow at work week or two ago so I threw it up on the rack to see if I could get it going. Cleaned the carbs (they actually looked really good except that the needles were in upside-down:huh), checked the timing, made sure it had oil and valve clearance, threw an aux tank and a battery charger on it and it fired right up.:lol3

    It smoked pretty good (I had put some oil in the cylinders) and the wiring harness was a total mess so I didn't want to run it long. Frankly, it startled me when it started. I wasn't really expecting it to fire:eek1. I shut it down and started to research the bike a bit. Yesterday I made a simple (temporary) wiring harness to get the charging and ignition in order. I had cleaned the inside of the tank and put new gaskets in the petcocks, did the rest of the motor maintenance and fired it up again. Seemed to run good, but still smoked a fair amount. I've seen that before with bikes that have sat for a long time and usually (but not always) the motor tightens up and the smoking quits after a few miles. We'll see with this one.:deal

    I'd been following bulldog1980's thread on his TX750 and got quite a bit of information from there. The 1973 models like mine have whole host of issues with the motors. There were significant recalls to try to fix the issues and the only one that I can see at this point is I do have the extended oil sump. Hopefully I also have the balancer adjuster mod. I should be able to find out in the next day or two.

    I'm not sure were I'm gonna take this one. It is way too far gone for a stock bike. Too bad because they were really good looking bikes stock:cry. It already has a backyard bob look that I kinda like, so I'll probably continue with that. And now I still need forks and wheels for the XS650:puke1
    #1
  2. concours

    concours WFO for 41 years

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    Those alloy rims were a beautiful rip off of an Akront, done by DID, (the chain people)
    #2
  3. HapHazard

    HapHazard Waiting for Gudenov

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    XS650 street trackers aren't exactly rare, but ANY TX750 is! Carry on!

    PS: As someone else would shortly ask anyway, "any pics?".:lol3
    #3
  4. pbarmy

    pbarmy Long timer

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    [​IMG]

    Here it is.:1drink
    #4
  5. SOS

    SOS Ignorance is a gift

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    Yep. :D Took some today while I was using the info that concours posted.

    Here is basically what it looks like minus a couple parts that I had taken off but not too many.



    [​IMG]

    [​IMG]

    [​IMG]

    The bike starts right up now. The tank has been cleaned, petcocks rebuilt, the motor is leak free though it is smoking pretty good. I need to get a compression check, but it seems to be very good. It is a 1973 so I did not know if the recalls (extended oil sump and balancer adjuster) were done, but it looks like they have.

    The extended oil pan:

    [​IMG]

    And the balancer adjuster, you can tell by the bending lock plate:

    [​IMG]

    The first time I started it before I pulled the wiring the charging system was working at least somewhat. When I turned the battery charger off it kept running. The wiring was such a mess I was afraid to run it much so I found a wiring diagram and started pairing it down to what I needed for the ignition and charging systems.

    Here is the original diagram:

    [​IMG]

    Then I cut it down to how I plan on running it. Eliminating the reserve lighting and other misc items:

    [​IMG]

    This is the way I have it wired right now. The ignition is fine but I am getting no charging at all. 12.5 volts on the unloaded battery and 12.1 with the bike running.

    [​IMG]

    I checked the connections and the original print again, but I don't see anything that would prevent the charging. There is no output from the stator. The stator is not grounded on any of the windings. I certainly didn't spend much time making up the harness, but it is per the last print.

    This bike has field windings so when I got no voltage from the stator I thought I wasn't getting power to the field windings, but I checked and I am getting 12 volts to ground on both wires (green and black). I can't find anything wrong with the diagram that I am using for start up (please chime in if you do) so at this point I think I need to build a harness with proper connections. I'd like to check the charging system and get a couple miles on the motor before I pull it out to start the project.:ear
    #5
  6. villageidiot

    villageidiot Long timer

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    apart from the abortion of a seat/tail, that thing is pretty rad
    #6
  7. pbarmy

    pbarmy Long timer

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    Seat,tail,battery box!Fucker was full of wasps when we fetched it from the boneyard.:eek1


    [​IMG]
    Cool engine.
    #7
  8. c1skout

    c1skout Been here awhile

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    Sweet! That's a regular hens tooth there.
    #8
  9. anonny

    anonny What could go wrong?

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    It's good to see you realize those 2 points about that particular bike.... it would be a shame to dump the necessary time and funds into a restoration only to have the motor fail.

    Pity to cuz they were a sweet looking bike, I had a friend buy one new but he wrecked it long before the motor could calve. :D
    #9
  10. SOS

    SOS Ignorance is a gift

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    From what I've read they can be reliable with the mods. I do like these bikes stock, but this one is not the bike for that. I am looking forward to riding this one around town though:D
    #10
  11. don-vee

    don-vee Adventurer

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    I'd knock that wasp box off the back with a sledgehammer, then cruise that everywhere and wake the neighbors. What a gnarly machine! Love it!
    #11
  12. concours

    concours WFO for 41 years

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    ....had mine doing the ton Sunday! :D
    #12
  13. SOS

    SOS Ignorance is a gift

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    Awesome! I think I'll put some brakes on and new shoes on before this beauty does the ton:lol3
    #13
  14. Ddouble

    Ddouble Been here awhile

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    I had one of these "back in the day". I loved it. More sophisticated than the 2 strokers that came before it, and I preferred it to my buddy's CB750. Nice looking, handled great, sounded good. I had 2 trouble free years with it until I stuffed it into an Oldsmobile. Stupid kid! (me).
    #14
  15. Sniper X

    Sniper X De Oppresso Liber

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    There's one here for sale cheap that is a runner.
    #15
  16. Sniper X

    Sniper X De Oppresso Liber

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    That is the worst seat tail thingy I have ever seen!
    #16
  17. concours

    concours WFO for 41 years

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    Where?
    #17
  18. concours

    concours WFO for 41 years

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    +1 I reckon that's what happens when kids with lot's of energy watch Monster Garage and American Chopper back to back. Reality show idea birth defects.:lol3
    #18
  19. SOS

    SOS Ignorance is a gift

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    Just when I decided to keep it :lol3

    Didn't get a chance to dink with it today. Too busy in the shop and had to get home right after closing.

    I was going to cut the back section off today, but I did look more closely at it and it is bolted on. I'll pull it tomorrow and see if I can stuff a battery behind the oil tank. The starter is long gone and I'd pull it anyway for a bike like this, so I don't need much in the way of amp-hours.

    I was thinking about my charging issue. I was getting 12 volts to ground on both the green and black wires to the field winding. With no output from the stator at all it seems like I have a field voltage problem. Looking at the diagram again there is a ground on the black wire so I should see no voltage black to ground and 12 volts green to black (aka ground).

    I didn't get a chance to look at the wiring today, but I'll check tomorrow. I'm certainly not an electrician, if you couldn't tell.:huh
    #19
  20. SOS

    SOS Ignorance is a gift

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    Lost the rear tail section:D And I'll be able to get a battery behind the oil tank:clap

    [​IMG]

    [​IMG]

    Also got the charging sorted out. It was the ground (or lack of ground) from the voltage regulator.:clap 13.8 volts at idle and about 14.7 with some rpm.
    #20