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My little CB100

This is a discussion on My little CB100 within the Project Builds forums, part of the Caferacer.net Forums category; Man, that thing looks cool. Nothing like that around here though. I'm still trying to get this little 100 dialed in......thinking I may have to ...

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  1. #61
    Member mitchi's Avatar
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    Man, that thing looks cool.

    Nothing like that around here though.

    I'm still trying to get this little 100 dialed in......thinking I may have to pull the engine "again" and have the head rebuilt, or at least check the valve seats.

    Keeps fouling plugs.
    "If it ain't raining, I'm riding"~~~~~~{iii}?~~~~~~~prost~~~~~

  2. #62
    Senior Member TrialsRider's Avatar
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    If the valve seats are compromised that should show on a compression test.
    ... is it fouling plugs or is the insulation around the centre electrode cracking and sparking way up inside the plug? <- that happens sometime.
    Fouling shouldn't happen near as much on a 4-stroke because there is no oil mix in the fuel.
    Does this have breaker points ignition? Spend some extra effort to make sure the points and condenser are perfect.

    You spent way too much effort on that bike to give it up now :|

  3. #63
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by mitchi View Post
    Man, that thing looks cool.

    Nothing like that around here though.

    I'm still trying to get this little 100 dialed in......thinking I may have to pull the engine "again" and have the head rebuilt, or at least check the valve seats.

    Keeps fouling plugs.
    Before you tear into the engine, try and take a few good closeup photos of the plugs. You need to determine if they are fouling because of oil consumption or running too rich. Worn guides or rings can cause the oil problem. Too rich it could just be the carb float level, seat leaking, wrong jets etc , but a weak spark will also allow the plugs to foul and look like it’s running rich.

    If you can’t get a decent photo, have a look around the net for info on plug reading. Things have changed because of ethanol and generally crap fuel, but you can likely figure out if it’s oil or too rich that is causing the problem. Do you have the correct plug?

    You can disconnect the black and white wire from the kill switch to temporary eliminate it from the system if you end up suspecting the ignition. It’s rare, but sometimes they can have some continuity to ground when they shouldn’t.. causes weak spark and the plug will foul. Before you do that, as Trials said make sure the points are ok and the condenser is also ok..... assuming you have points in there.

    Ps.... unfortunately you can’t assume all is well with your new aftermarket carb, You can’t even assume the numbers on the jets have any bearing on what they actually flow.
    Last edited by Cyorg; 10-11-2019 at 08:12 AM.
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  5. #64
    Senior Member crazypj's Avatar
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    Quote Originally Posted by Cyorg View Post
    Ps.... unfortunately you can’t assume all is well with your new aftermarket carb, You can’t even assume the numbers on the jets have any bearing on what they actually flow.
    That's a good point. If you bought a cheap replacement carb the first thing to do is pull it apart to check everything. As pointed out, E10 fuel is slightly less dense than non - ethanol fuel so increasing float level by 1mm would be a good idea. If it's a points motor, it will be grounding when points are closed, completing circuit through ignition coil. If it's a later electronic ignition it won't have battery power to system. (unlikely unless someone modified parts to fit 100) It would be simple enough to check voltage at points when they are open, should be very close to battery voltage, within 0.5v. Anything more (1.5~2v) shows you have high resistance in wiring or connectors, switch, etc.


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  6. #65
    Senior Member TrialsRider's Avatar
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    Note:
    Carb float levels can be a huge deal on trials bikes where you regularly do extreme nose down or nose up riding.
    If it messes up in one direction only and not the other, the float level is likely the problem otherwise
    keep looking.

  7. #66
    Member mitchi's Avatar
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    New spark plug, fires but sputters some.

    Filled the tank all the way.......runs great. No sputter, no hesitation, gits up and goes.

    So bottom line, may be carb issue. huh?

    I have the original carb, and am rebuildin it.

    We'll see.
    Last edited by mitchi; 11-02-2019 at 06:45 AM.
    "If it ain't raining, I'm riding"~~~~~~{iii}?~~~~~~~prost~~~~~

  8. #67
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by mitchi View Post
    New spark plug, fires but sputters some.

    Filled the tank all the way.......runs great. No sputter, no hesitation, gits up and goes.

    So bottom line, may be carb issue. huh?

    I have the original carb, and am rebuildin it.

    We'll see.
    Or you could just clean the screen on the fuel tap.

    Ps.. make sure the cap vent is clear while you’re at it.
    Last edited by Cyorg; 11-02-2019 at 12:34 PM.
    "Non urinat in ventum"

  9. #68
    Member mitchi's Avatar
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    Cap is new, petcock is new.

    Fuel tank was cleaned with evaporust.

    I will pull the bowl off again.

    I do have a gassy smell while running, and after I shut it down.
    "If it ain't raining, I'm riding"~~~~~~{iii}?~~~~~~~prost~~~~~

  10. #69
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    I do have a gassy smell while running, and after I shut it down.[/QUOTE]

    You might want to consider some changes to your diet.

  11. #70
    Member mitchi's Avatar
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    Quote Originally Posted by upperb View Post
    I do have a gassy smell while running, and after I shut it down.
    You might want to consider some changes to your diet.[/QUOTE]

    Ha ha........yea, kinda set myself up on that one..
    "If it ain't raining, I'm riding"~~~~~~{iii}?~~~~~~~prost~~~~~

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