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  1. #1
    CB750 Member MotersickleBum's Avatar
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    Craigslist 1981 CB750 for $250

    ok, i just bought a black 81 cb750 today off of craigslist for $250.00. it's got 4007 miles on the odometer. i couldn't go wrong. it does not currently run though but the guy gave me a brand new battery and repair manual and sundry parts. here's a pic as it was on craigslist. it's now on my trailer in my driveway. this will be a fun project. this mofo is going to run well.
    Attached Thumbnails Attached Thumbnails 00G0G_1F8gD3PRtNF_1200x900.jpg   00X0X_3B4w6xeQAzi_1200x900.jpg  

  2. #2
    CB750 Enthusiast pidjones's Avatar
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    Congrats! Sure looks a lot nicer than my $250 '79 CB750F.
    "Love 'em all.... Let GOD sort 'em out!"

  3. #3
    CB750 Member MotersickleBum's Avatar
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    Quote Originally Posted by pidjones View Post
    Congrats! Sure looks a lot nicer than my $250 '79 CB750F.
    it's not bad.... some surface rust on the front rim and it could use paint. first things first though, i'm going to pull the plugs and put some oil in the cylinders then see if i can get it to crank-over. THEN i'll check for spark. THEN i'll squirt a little juice in the carbs to see if i get fire. if so, getting it running will be easy.

    do you know if this is a "K" or a "C" (custom)

  4. #4
    CB750 Enthusiast pidjones's Avatar
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    You can cross the VIN on the headstock. There are lists online to tell you. Here is one: https://www.motorcyclespareparts.eu/...a-model-prefix
    "Love 'em all.... Let GOD sort 'em out!"

  5. #5
    CB750 Member MotersickleBum's Avatar
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    ok, thanks! but i did some basic troubleshooting and i was getting very very weak spark and then no spark. someone changed the plug wires so i put the originals back on and still weak to no spark. i have to see what The Book says. but everything lights up, it has compression and the starter works good so i'm assuming that this is not a major problem.

  6. #6
    CB750 Enthusiast pidjones's Avatar
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    I would first check the voltage and connections powering the coil and ignition packs. Build-up of oxidation can drastically cut that voltage (and the current the joint can carry) down.
    "Love 'em all.... Let GOD sort 'em out!"

  7. #7
    CB750 Member MotersickleBum's Avatar
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    Quote Originally Posted by pidjones View Post
    I would first check the voltage and connections powering the coil and ignition packs. Build-up of oxidation can drastically cut that voltage (and the current the joint can carry) down.
    i'll clean all the connections and try again. i had very weak spark on one plug. the electrical stuff i don't know about. i'm getting voltage at the right coil but not sure if i'm testing properly on the other side. is there a no spark troubleshooting tutorial here?

  8. #8
    CB750 Enthusiast pidjones's Avatar
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    The FSM (available for download in pdf form online) has one. Here is a good copy: http://www.dotheton.com/forum/index.php?topic=44399.0
    Ignition troubleshooting is in Chapter 17, but you should download it all.
    Last edited by pidjones; 11-07-2018 at 07:18 AM.
    "Love 'em all.... Let GOD sort 'em out!"

  9. #9
    CB750 Member MotersickleBum's Avatar
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    cool, thanks... but actually this doesn't tell you the steps to check defective electronics et. it just tells me the likely causes which i already know. this is better: https://www.denniskirk.com/learn/how...ose-motorcycle
    Last edited by MotersickleBum; 11-07-2018 at 07:40 AM.

  10. #10
    CB750 Enthusiast pidjones's Avatar
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    Actually, Chapter 17 has step-by-step procedures for checking each module. And this is specific to the dohc 750s, not generic.
    Quote Originally Posted by MotersickleBum View Post
    cool, thanks... but actually this doesn't tell you the steps to check defective electronics et. it just tells me the likely causes which i already know. this is better: https://www.denniskirk.com/learn/how...ose-motorcycle
    "Love 'em all.... Let GOD sort 'em out!"

  11. #11
    CB750 Member MotersickleBum's Avatar
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    maybe my computer isn't downloading it properly....i'm watching this now. it's pretty good..
    https://www.youtube.com/watch?v=jaSKU2m3qbI

  12. #12
    CB750 Enthusiast pidjones's Avatar
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    "Love 'em all.... Let GOD sort 'em out!"

  13. #13
    CB750 Member MotersickleBum's Avatar
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    ok, thanks!

  14. #14
    CB750 Member MotersickleBum's Avatar
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    ok, I NOW HAVE SPARK! i did the easy stuff first and cleaned all the connections at the coil et and i have a good arch on all four coils! far out! but, i only have two ignition wires so i need to get some more. i was surprised that i didn't have a set in my bin of old motorcycle parts. i will likely need new resister plug boots too. i'll ohm those out to be sure. i didn't think that it was something serious because the bike only has 4007 miles on it and everything else works even the horn. anyone have any old wires hanging around?

  15. #15
    CB750 Enthusiast pidjones's Avatar
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    You should be able to pick some up at any auto parts store. The ends just screw in. Caps should be 5k ohm.
    "Love 'em all.... Let GOD sort 'em out!"

  16. #16
    CB750 Member MotersickleBum's Avatar
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    the auto parts will have these wires with the heavy gauge copper core? cool....the guy tried to put some car wires on it and that wasn't working at all. i'll check the caps tonight.

    thanks!

  17. #17
    CB750 Member MotersickleBum's Avatar
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    only one of the caps was good. weird. but now that i have spark i should be able to test for fire soon. this is going to be fun.

  18. #18
    CB750 Enthusiast pidjones's Avatar
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    Two of mine (the straight two) were bad. NGK caps are readily available. And they have a replaceable resistor element.
    "Love 'em all.... Let GOD sort 'em out!"

  19. #19
    CB750 Member MotersickleBum's Avatar
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    replaceable resistors are a good idea. all NGK caps have replaceable resistors?

  20. #20
    CB750 Enthusiast pidjones's Avatar
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    I don't know, but the caps on my GL1000 are NGK, and they have replaceable resistors.
    Quote Originally Posted by MotersickleBum View Post
    replaceable resistors are a good idea. all NGK caps have replaceable resistors?
    "Love 'em all.... Let GOD sort 'em out!"

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