Black plugs Black exhaust on my CB750
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Black plugs Black exhaust on my CB750

This is a discussion on Black plugs Black exhaust on my CB750 within the Technical forums, part of the Caferacer.net Forums category; Hey whatsup .....haven't been on here fer awhile. I just been down to get my '74 CB750 up and running after cleaning out the tank ...

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  1. #1
    wildcatmahone's Avatar
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    Black plugs Black exhaust on my CB750

    Hey whatsup .....haven't been on here fer awhile. I just been down to get my '74 CB750 up and running after cleaning out the tank and carbs REAL GOOD.Even put on new fuel lines, clean petcock. And it's like this...I pulled out the choke and she started right up. She was revving pretty sweet but wouldn't idle then slowly lost power.Turned OUT the idle screws a 1/2 turn checked the plugs and they were all carbon fouled. Got my plug file and cleaned them up.Tried again and she was revving but for a shorter amount of time and then stalled. Another half turn of the idle screws, cleaned each plug again and the same shit happened again. Any suggestions-shit, any shops that will take a '74 CB750? I'm fuckin' fed up...<img src=icon_smile_tongue.gif border=0 align=middle>

    Touraloualay...
    '73 CB350(RIP)
    '74 CB750K3 Cafe Thriller

  2. #2
    Senior Member krapfever's Avatar
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    Are the plugs black and sooty? Or black and oily?

    How do the carbs look inside?



    Honda go sideways!

  3. #3
    Senior Member xander450's Avatar
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    In order to diagnose fouled plugs, you'd need to say more... I mean, everything. Was there a time when it didn't foul plugs with EXACTLY the same configuration (i.e. you haven't installed a carb kit, different air cleaners, exhaust, etc), and what happened since then? Are you running stock air filters/exhaust? What plugs are you using, and are they the correct heat range? Are the jets/needles correct for that bike/elevation - did you check? Did you by chance clean out your jets with a file?

    I find float levels are often the overlooked component in a carb rebuild. Check to see that they're in spec.

    I recommend not paying someone to do this - what you're doing is what's known as dues. If the crap on your plugs is fluffy and dry, your bike isn't BROKEN as such - it is simply out of adjustment, clogged or otherwise buggered up. Knowing how to clean and tune a carb is the cost of owning a vintage bike.

    There was a time when it really irritated me that these carbs required so much attention. Then I figured out why they're always on craigslist for five hundred bucks, and it made me feel all fuzzy and warm.

    A



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  5. #4
    Senior Member snorkelfork's Avatar
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    i say this out of mercy not to sound like a dick or as if wer'e ganging up on you but xander is absolutely right. if you're fed up already then you might ought to seriously consider selling the bike now and saving yourself from a series of future headaches.

    if you resort to mechanics to do menial but troublesome work you are going to lose your ass in repair costs. in addition just because a guy works on bikes doesn't mean he knows jack shit about fixing your vintage honda. sure the basics for most bikes are the same but each honda model has quirks unique to it and unless they've owned one themselves or really done their homework they will give you your bike back half ass repaired along with a bill for the time they spent scratching their heads in wonder.

    that all said give use some details of the situation...

    ...connoisseur of slack...


    Edited by - snorkelfork on Jul 16 2007 01:43:36 AM

  6. #5
    wildcatmahone's Avatar
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    Hey yes they are black and sooty, the plugs and the exhaust too. So I've had the bike since April, it came from Georgia. She was running fine with absolutely no problems, she came with 4 into 1 pipes and uni filters. Then about a month and a half after she started idling worse and worse and started backfiring a bit. Changed the plugs to fresh ones from NGK D8EA to NGK D8ES and still the same problem. Cleaned my tank, petcock, put new fuel lines on, and then pulled the carbs which were really clean to begin with. Installed a fresh set of pod filters. I've been told that I could be running too rich through the carbs but the idle screws dont seem to help much with this. Hey do think there's any chance that it needs to be rejetted because of her new home from GA to NY?

    Cheers

    Touraloualay...
    '73 CB350(RIP)
    '74 CB750K3 Cafe Thriller

  7. #6
    Moderator joe c's Avatar
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    is the choke working? maybe the cable's broke?

    id say you wouldnt have to rejet for that. your both pretty much at sea level. is it all of the plugs, or just one or 2? i know you said all carbon fouled, you mean all of the plugs, right?

    jc






  8. #7
    Senior Member kenessex's Avatar
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    Choke! Only thing common to all 4 cylinders. Symptoms are right too. Revs nice when cold then dies and fouls plugs.
    Check the linkage at the carbs.

    Ken

    Only other outside possibility could be ignition if somebody switched from points to some vintage electronic system that uses a single black box. Not likely

    AHRMA 412
    Vintage racing - old guys on old bikes

  9. #8
    Senior Member Geeto67's Avatar
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    how long are you running it with the choke lever pulled up (on)? With a cb750 you should only have to run it for a couple of seconds before you close the choke and allow it to warm up. any more than that and plugs foul aplenty.

    Pods are shitty on a cb750, get yourself a stock airbox and a K&N filter element for it and you'll see your bike's idle quality improve drastically.


    check your points cover and see if you have a martek 440 ignition setup - it is the only single balck box vintage ignition system for a cb750 that I know of (dyna makes new ones that are much better).


    Edited by - geeto67 on Jul 16 2007 10:02:54 AM

  10. #9
    lefty337's Avatar
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    Hey Geet, thanks for the info. I was thinking about putting pods on my cb750f eventually.

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