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Mulan-Is she starving or over eating?

This is a discussion on Mulan-Is she starving or over eating? within the Technical forums, part of the Caferacer.net Forums category; Well theres a lot of talk about the gas cap so exactly what am i looking for?-i did recently replace the cap rubber and it ...

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  1. #21
    Senior Member surfrider70's Avatar
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    Well theres a lot of talk about the gas cap so exactly what am i looking for?-i did recently replace the cap rubber and it seems to lock down just fine and be seal nicely when i close it, am i missing something? And the petcock has been completely redone as mentioned previously.
    And can someone explain how a leaky gas cap leads to overfilled bowls and puddles on the ground out of only certain carbs?
    Again forgive my general moto naivete im a newb...

  2. #22
    Banned DohcBikes's Avatar
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    What's a moto?

    Let me read this thread and see if I can figure it out.

    Fair warning though, i've recently been self diagnosed with bipolar, ptsd, manic-depression, adhd and a myriad of other mental illness that cause me, through no actual fault of my own, to be a complete asshole at times, or possibly just have a complete emotional breakdown until somebody tells me it will be ok.

  3. #23
    Member scramblermike's Avatar
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    It's not the rubber seal that is the problem. When your cap is up look and you will see a small hole that allows air to get through. Just blow on the vent hole to see if it's clear. If it's blocked then that's you problem. Seen it many times

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  5. #24
    Senior Member Teazer's Avatar
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    Quote Originally Posted by scramblermike View Post
    It's not the rubber seal that is the problem. When your cap is up look and you will see a small hole that allows air to get through. Just blow on the vent hole to see if it's clear. If it's blocked then that's you problem. Seen it many times
    And sometimes it because the cap gasket (rubber ring) was replaced with one that was a little larger and it covered up the breather hole.
    surfrider70 likes this.

  6. #25
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by surfrider70 View Post
    Well theres a lot of talk about the gas cap so exactly what am i looking for?-i did recently replace the cap rubber and it seems to lock down just fine and be seal nicely when i close it, am i missing something? And the petcock has been completely redone as mentioned previously.
    And can someone explain how a leaky gas cap leads to overfilled bowls and puddles on the ground out of only certain carbs?
    Again forgive my general moto naivete im a newb...
    Allow me to expand on what the guys are saying about your fuel filler cap :| That concern relates to the problem you experienced with the engine cutting out after operating for some period of time, your fuel tank relies on gravity feed and therefore the fuel tank must be vented to atmospheric pressure or evacuation of the fuel into the engine can potentially create a vacuum inside the tank, which eventually starves your carburetors for fuel (all of them, not just one or two)
    This potential problem does not relate to the fuel leak and it really doesn't match the power loss symptoms as I read them.
    On the fuel leaking issue, the carburetors should only leak fuel out of the over-flow tubes as long as there is fuel still coming into them, so with the fuel tap off, you really should not be seeing much leakage as the result of a stuck open or needle and seat or float not floating problem :/ that is another reason I recommend you collect any fuel that is exiting those ports, I suspect you might have a fuel leak somewhere else. BTW if you collect into an open pan the fuel will evaporate fairly quickly, but if you collect it into a container that has a small opening or even a plastic bag <- you won't lose any fuel to evaporation. Hint, hint you could even put a plastic baggie around an entire carburetor body if there was any concern it was leaking out of somewhere other than the overflow vent pipe.

    Now lets get back to your motor performance taking a shit on occasion; IF you can determine that 2 cylinders have wet spark plugs and 2 cylinders look like that are happy, you can trouble-shoot the coils by swapping them between on another and if the problem starts happening to the other 2 cylinders instead you just proved it's a coil. Same test could be applied to the points and condenser (if so equipped) as all of those parts are frequently identical pairs of gizmo's. If you're a cheap prick like me who lives in the woods and a long way from replacement parts supplies, but have some time on your hands, that's how you could determine what parts you truly need without replacing expensive stuff at random.

    Oh, oh gotta go, suppers ready and I'm freakin starved.

  7. #26
    Senior Member surfrider70's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Allow me to expand on what the guys are saying about your fuel filler cap :| That concern relates to the problem you experienced with the engine cutting out after operating for some period of time, your fuel tank relies on gravity feed and therefore the fuel tank must be vented to atmospheric pressure or evacuation of the fuel into the engine can potentially create a vacuum inside the tank, which eventually starves your carburetors for fuel (all of them, not just one or two)
    This potential problem does not relate to the fuel leak and it really doesn't match the power loss symptoms as I read them.
    On the fuel leaking issue, the carburetors should only leak fuel out of the over-flow tubes as long as there is fuel still coming into them, so with the fuel tap off, you really should not be seeing much leakage as the result of a stuck open or needle and seat or float not floating problem :/ that is another reason I recommend you collect any fuel that is exiting those ports, I suspect you might have a fuel leak somewhere else. BTW if you collect into an open pan the fuel will evaporate fairly quickly, but if you collect it into a container that has a small opening or even a plastic bag <- you won't lose any fuel to evaporation. Hint, hint you could even put a plastic baggie around an entire carburetor body if there was any concern it was leaking out of somewhere other than the overflow vent pipe.

    Now lets get back to your motor performance taking a shit on occasion; IF you can determine that 2 cylinders have wet spark plugs and 2 cylinders look like that are happy, you can trouble-shoot the coils by swapping them between on another and if the problem starts happening to the other 2 cylinders instead you just proved it's a coil. Same test could be applied to the points and condenser (if so equipped) as all of those parts are frequently identical pairs of gizmo's. If you're a cheap prick like me who lives in the woods and a long way from replacement parts supplies, but have some time on your hands, that's how you could determine what parts you truly need without replacing expensive stuff at random.

    Oh, oh gotta go, suppers ready and I'm freakin starved.
    Ok so here is a pic of the gas cap-im assuming the little vent hole there off center leads to an opening under the cap but on the other side of the new rubber effectively venting the tank for vaccum purposes-man thats a tiny hole!
    I blew on it the best i could-dont know if it did anything and i could not find wire small enough gauge to try and rod out but i can-so in theory if this tiny vent hole is blocked a simple ream out will solve the problem of the engine cutting out, but not the leaking carbs correct?

    I have looked everywhere without the tank off and can find no other evidence of a fuel leak pre-carbs but ill look more thoroughly. Its just when i see the wet tips of the float bowl overflow lines i just assume thats the culprit.

    Per a receipt i saw before i bought it, the points and condenser were overhauled-i know what youre thinking-what the hell does overhauled mean?!-i get it. Im going to look for nice clean spark, and dry plugs before i go much further.

    Im intrigued and hopeful these two issues are not related-the vent cap blockage would be a nice easy fix, its the fuel dumping that has me flummoxed.

    Thanks gents this is all great stuff and im learning a ton!Name:  IMG_0967.JPG
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  8. #27
    Senior Member TrialsRider's Avatar
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    Two things to note: To trouble-shoot a gas tank vent problem, when the trouble happens just pop open the cap and if the problem suddenly resolves for a while you found the problem. Second thing, the vent is never a straight through hole, if it was fuel would splash around inside the almost full tank and leak out the vent. On a locking gas cap the vent sometimes shares the key hole. (not likely the case on yours because your key is not in the cap)
    I guess this is a third thing :/ if there is a lot of fuel in the tank it won't take long to create a vacuum, but if the fuel is low, it will take a lot longer to create a significant vacuum in the tank and create the problem.
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  9. #28
    Senior Member TrialsRider's Avatar
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    Re: points and condenser; the condenser is just a simple paper type capacitor, they can go wrong at any time and are cheap to replace, I would imagine they are also relatively easy to substitute. Condenser must be well grounded to function and the wire lead is usually kept as short as possible to perform efficiently. The points are very model specific, can go bad in several ways; the contacts can become dirty, carbon up and or pitted and melted. The phenolic block that rubs against the cam is constantly worn away which is why the occasionally need to be adjusted. (There is often a little felt block with some oil on it, located next to the block and that is to keep things sliding nicely and free of rust.) The points are spring loaded and that spring usually acts as the conduit for the electrical charge, it needs to be insulated from any chassis ground. The point pivot on a tiny shaft and if that gets rusty or seizes or shorts out the points in any way that will cause them to stop functioning.

    An "overhaul" of your points lol would do nothing to address the wear on the phenolic block and they would usually just run some emery paper over the point contacts which also serves to further reduce the thickness of material on there. They might have oiled up the parts a bit or maybe not. Personally; I don't trust your average motorcycle mechanic to give 2 shits about your motorcycle just as long as it is running when you pay the bill. The parts they put on a bike are usually because they had them on hand and wanted to sell them, or absolutely needed them to make it run. Overhauling disposable parts means they could not procure a replacement part but the part absolutely needed attention to make it run.

    Bottom line is Points are the weakest point in the system because they actually wear out by design, capacitor and coil would be a close second in likelihood to fail.

    ... there's a whole bunch of info for you to contemplate, and it still might not be your current problem but the price is right.
    surfrider70 and 540nova like this.

  10. #29
    Senior Member surfrider70's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Re: points and condenser; the condenser is just a simple paper type capacitor, they can go wrong at any time and are cheap to replace, I would imagine they are also relatively easy to substitute. Condenser must be well grounded to function and the wire lead is usually kept as short as possible to perform efficiently. The points are very model specific, can go bad in several ways; the contacts can become dirty, carbon up and or pitted and melted. The phenolic block that rubs against the cam is constantly worn away which is why the occasionally need to be adjusted. (There is often a little felt block with some oil on it, located next to the block and that is to keep things sliding nicely and free of rust.) The points are spring loaded and that spring usually acts as the conduit for the electrical charge, it needs to be insulated from any chassis ground. The point pivot on a tiny shaft and if that gets rusty or seizes or shorts out the points in any way that will cause them to stop functioning.

    An "overhaul" of your points lol would do nothing to address the wear on the phenolic block and they would usually just run some emery paper over the point contacts which also serves to further reduce the thickness of material on there. They might have oiled up the parts a bit or maybe not. Personally; I don't trust your average motorcycle mechanic to give 2 shits about your motorcycle just as long as it is running when you pay the bill. The parts they put on a bike are usually because they had them on hand and wanted to sell them, or absolutely needed them to make it run. Overhauling disposable parts means they could not procure a replacement part but the part absolutely needed attention to make it run.

    Bottom line is Points are the weakest point in the system because they actually wear out by design, capacitor and coil would be a close second in likelihood to fail.

    ... there's a whole bunch of info for you to contemplate, and it still might not be your current problem but the price is right.
    Great info as usual Trials-i can feel myself getting smarter!

    Im gonna take her for a spin and pop the cap when she starts acting up and see what happens. If nothing happens can we assume we can put to bed the bad cap theory? If it runs great post cap pop im gonna buy a proper NOS cap and assume it will vent properly, i would like one anyway to get rid of the ghetto rigged one on there now.

    I will also check out the points and see if i can see something obvious. The points are new for me-i get how they work and can ask my bro to help with anything serious. I too am wary of any mechanic but it was before i bought it and pretty much any shade-tree moto mechanic knows more than i do.

    As far as carbs go-with the petcock off for 2 days im still getting a puddle-the bike is leaning on the kickstand side obviously and when i straightened her up she dribbled a float bowl (roughly) portioned amount of gas onto the ground from the carb furthest away from the petcock-wouldnt the carb closest to the petcock be the first to dribble and why is there anything in these floats if the petcock is off?

  11. #30
    Senior Member Cyorg's Avatar
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    Haven't read all of this,but.. do you have a fuel filter? If opening the cap doesn't help to clear things up. You could drain one or two of the float bowls into a small container so you know how much fuel should be in each bowl. Drive the bike until it acts up. If you don't have any open road handy, then take a couple of rotund passengers along. When it starts to act up, pull over and shut the fuel tap off. Start draining the float bowls one by one to verify they have enough fuel in them. If they are low and assuming opening the cap on your previous ride didn't help.... if you have a filter that could be slowing the gravity fed fuel to the point where it can't replenish it fast enough to maintain the proper float level. Same thing goes for kinked lines, lines that are too small, plugged screen, wrong fuel tap and so on. This doesn't explain your puddle though, but as previously explained, the lack of venting could cause pressure to overcome a questionable needle and seat.
    If any or all of this has been previously covered... sorry carry on.
    surfrider70 likes this.
    "Non urinat in ventum"

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