'86 FZ750 spark issue.....
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Thread: '86 FZ750 spark issue.....

  1. #1
    Chris King
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    '86 FZ750 spark issue.....

    Do the wires at the mini-coils under the tank come out or do I have to replace the unit?

    "Fun" part is that cylinders 1 and 2 are cold -- exhaust pipes I can physically touch them for far too long after I start the bike. That would mean that I need to replace BOTH units because they go 1/4 and 2/3 I believe.

    Spark plug #1 (far left as you sit on the bike) appears virginal and smells of gas, but when I pulled the wire out of the boot and stripped it, there was SOME spark -- maybe just not enough.

    Yes, I swapped the boot so I'm thinking there's just not enough spark to make it fire down there.....

    Spark plug #2 appears to be firing when I pull it out, but again not as hot as it should be, so in essence the bike is running on 3 cylinders.

    Which sucks because the engine is the best thing about an FZ750.

    Anyone else with this wonderful old beast have this issue?

    TIA,

    -c

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  3. #2
    Moderator Array TeeTee's Avatar
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    Either your bike has a different firing order or something else is amiss. If both Y coils were acting up it wouldn't run at all. Since it sounds like you had the tank off or can see the wire runs it's easy to trace the spark leads to see which coil feeds what cylinders.

    You say you can hold your hand on those pipes for far too long. But that implies that they are still heating up but not as fast as the other two. That sounds more like a weak firing than a coil failure. Badly out of synch carbs could do that. Or badly fouled plugs perhaps? Other wise it could really only be that those two spark leads are defective.

    Or you were messing with things and put the leads on two of the wrong plugs?
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  4. #3
    Chris King
    Guest
    Yes, there is weak firing and in cylinder #1 I swear it appears like no firing, but the exhaust does get warm.

    I'm going to have those leads tested, but I've swapped them for the old ones on my bike that were still "Okay" and got no difference. I'll have them tested.

    Again, on the coils issue i'm positive that the coils are split in that they don't serve 1/2 and 3/4.

    The carbs don't seem that badly out of sync (had them off and visually checked everything with my shop guy, so how far off could they really be) but that's what I'll be checking next -- just had to get a new chain and sprocket set, that comes first you bet

  5. #4
    Chris King
    Guest

    Good lord, all better now.

    Man, somehow I DID mark the wires the wrong way, it's not the caps a-tall.

    So with smoke billowing out of both pipes (remember, it was 1 and 2) I railed out for a 'round the block ride. Let me tellya what:

    That M-F is waaaay fast, 'cos I did have the carbs pretty much nailed down and 'cos we determined when fitting the sprocket/chain last week, it's got an FZR 600 set on it so you know it wants to come up with little provocation in 1-2-3.

    THAT's the FZ750 I came to know and love over the past year and 10,000 miles.

    Going for a ride from lower CT (Norwalk) to Boston/NH tonight to launch a new online movie with my film maker; soon we'll do bike vids too.

    http://kingcast.net
    http://justiceforkids.net

  6. #5
    Moderator Array TeeTee's Avatar
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    Quote Originally Posted by Chris King
    Man, somehow I DID mark the wires the wrong way, it's not the caps a-tall......
    It's always those simple things that bite us in the ass, ain't it? If I helped jog a few grey cells for you then you're welcome.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  7. #6
    Chris King
    Guest
    You sure did spike the grey matter and for that I (and the girlies I ride) thank you.

    The Kids and squids on their modern 600s don't =^.)

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