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Post by classacted on Aug 3, 2023 10:29:54 GMT -5
we never heard from the original poster if he fixed his sputtering issue.
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timwhite74
Scoot Junior
Posts: 16
Location: Las Vegas, NV
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Post by timwhite74 on Aug 3, 2023 20:27:33 GMT -5
Update: put on a new pet cock = no change. Took apart the carb and it’s clean but ran guitar string thru the jets to be sure. Float valve looks fine, moves freely. I even swapped the CDI. BUT NOW the sputtering is very consistent which is a good thing. It goes like this: starts and idles great, when riding around up to ~20% throttle is smooth, once I give it more than ~20% throttle it sputters and loses power/speed every time. At least it’s consistent, but I don’t know where to go from here. Doesn’t the carb use different jets depending on throttle/fuel needs? Could it be a bad jet? I’m thinking to “f” the whole thing and just buy a new carb. It has a Chinese carb on it now. Thanks
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Post by aeroxbud on Aug 4, 2023 2:58:20 GMT -5
Update: put on a new pet cock = no change. Took apart the carb and it’s clean but ran guitar string thru the jets to be sure. Float valve looks fine, moves freely. I even swapped the CDI. BUT NOW the sputtering is very consistent which is a good thing. It goes like this: starts and idles great, when riding around up to ~20% throttle is smooth, once I give it more than ~20% throttle it sputters and loses power/speed every time. At least it’s consistent, but I don’t know where to go from here. Doesn’t the carb use different jets depending on throttle/fuel needs? Could it be a bad jet? I’m thinking to “f” the whole thing and just buy a new carb. It has a Chinese carb on it now. Thanks Does it sound rich? If so you could Try moving the needle clip up a notch.
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Post by GrumpyUnk on Aug 4, 2023 9:18:09 GMT -5
When poking around, did you remove and inspect the emulsion tube? The main jet is mounted into the bottom of the tube, and the needle pokes in from the other end(top). Have you checked that the slide moves freely, and that the vacuum diaphragm is flexible and intact? If you move the needle up, it will enrich the mix, down will lean it out. If the needle is bent, or contacts the emulsion tube, it can become a bit stiff and not want to move when the engine rpms increase and want more fuel:air mixture fed into the intake. That will tend to choke it out... So, use a digit to check that it moves freely in both directions. The pilot jet seems to be the section that has problems unless it gets worse as the rpms increase past the stumble spot. The carb transitions as flow increases, from idle to pilot to main to the slide being fully open. If the pilot is too small or too large the transition from idle to intermediate will have problems as reported. tom
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timwhite74
Scoot Junior
Posts: 16
Location: Las Vegas, NV
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Post by timwhite74 on Aug 4, 2023 10:20:31 GMT -5
Thanks again aeroxbud and GrumpyUnk. I believe it sounds rich because when it stumbles and sputters, the exhaust sometimes backfires and pops. The needle and diaphragm looked good and moved freely. GrumpyUnk I thought the same thing and tried giving it more gas past the stumbling point (20% throttle), and it doesn't get better...just keeps bogging down and almost stalling. I'll move the needle clip up 1 notch today. Thanks again, guys. Very much appreciated.
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Post by GrumpyUnk on Aug 5, 2023 8:54:46 GMT -5
Stated in different words: something is causing the mix to go too rich once out of the idle circuit. First thing to check would be the float level. Or sticky/jamming. Did you check that the float would be level with the carb inverted? The weight of the float should close the needle valve, and leave the float just about parallel to the horizon(not the float bowl gasket surface) when the carb is inverted. Adjustment is fun. Get out a cigarette lighter and a screwdriver, get the driver hot, apply to the float tab as needed. Check. Rinse. repeat. tom
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timwhite74
Scoot Junior
Posts: 16
Location: Las Vegas, NV
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Post by timwhite74 on Aug 5, 2023 13:30:37 GMT -5
GrumpyUnk yes, adjusting the carb is the highlight of my day especially since I dropped the needle clip this morning and it fell into a black hole. I’ll check the float level as well. And while I’m at it rebuild the engine while blindfolded…j/k …just frustrated with what I thought would be a fun lil toy to ride around on.
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Post by aeroxbud on Aug 5, 2023 16:43:10 GMT -5
We have all been there with those pesky clips.
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timwhite74
Scoot Junior
Posts: 16
Location: Las Vegas, NV
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Post by timwhite74 on Aug 6, 2023 2:48:37 GMT -5
Stated in different words: something is causing the mix to go too rich once out of the idle circuit. First thing to check would be the float level. Or sticky/jamming. Did you check that the float would be level with the carb inverted? The weight of the float should close the needle valve, and leave the float just about parallel to the horizon(not the float bowl gasket surface) when the carb is inverted. Adjustment is fun. Get out a cigarette lighter and a screwdriver, get the driver hot, apply to the float tab as needed. Check. Rinse. repeat. tom I checked the level of the float and it was truly level and pressing well on the float needle. I also tried every notch on the main jet needle and that didn’t help either. Obviously, the lowest notch which pulls the needle up the highest was the worst setup (makes sense). It feels like the main jet needle moves freely and it’s straight. The only thing I’m not clear on is how the float and float valve play a role here. FYI, when is starts to sputter I go ahead and twist the throttle all the way open just to experiment and it causes the engine to sputter worse and die within about 10 seconds. If I let go of the throttle just before death it goes back to a smooth idle. Thanks again for all your suggestions and help! 😁
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Post by aeroxbud on Aug 6, 2023 3:34:14 GMT -5
The float and float needle control how much fuel is in the carb bowl. As the fuel level rises, the needle presses against the seat. This blocks fuel from entering into the carb.
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Post by classacted on Aug 6, 2023 9:56:38 GMT -5
timwhite74, did you ever get a new carb and try it? I thought you mentioned you might do that?
if you ever find the cause, please come back and let us know.
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Post by GrumpyUnk on Aug 6, 2023 10:38:07 GMT -5
QUOTE:|The only thing I’m not clear on is how the float and float valve play a role here. ??? FYI, when is starts to sputter I go ahead and twist the throttle all the way open just to experiment and it causes the engine to sputter worse and die within about 10 seconds. If I let go of the throttle just before death it goes back to a smooth idle."
If it was too rich, opening the throttle further would allow more air to enter, and the engine should run better. If it was lack of fuel, it would sputter, and then if opened further, would run worse, as opening allowed in more air.... I would suspect lean rather than too much fuel for the above reasoning. I have forgotten if you have pulled and inspected the main jet and emulsion tube. The fuel in the bowl gets sucked up through the main jet(if it is not clogged) and has some air injected into the liquid by means of the holes in the side of the emulsion tube. What forms then is fuel with bubbles in it... which is then sucked up around the needle and fed into the venturi and then the intake. Have the seals between the intake elbow and carb and intake elboe and cylinder head been checked for leaks? Cracks? Cracked rubber tubing/vacuum lines? Any leakage will throw off the mixture. The O-rings on the carb and on the elbow can get hardened with age and allow leaks. As posted elsewhere, a smear of RTV across the O-rings can help reseal the joints. tom
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timwhite74
Scoot Junior
Posts: 16
Location: Las Vegas, NV
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Post by timwhite74 on Aug 6, 2023 14:21:08 GMT -5
classacted I haven't bought a new carb yet. I'll definitely come back when/if this carb issue is resolved. GrumpyUnk Being too lean NOW makes more sense here. "If it was too rich, opening the throttle further would allow more air to enter, and the engine should run better. If it was lack of fuel, it would sputter, and then if opened further, would run worse, as opening allowed in more air..." <- this takes me back to the original issue of fuel delivery and why I put on a new pet cock. I ran a magnet around the bottom of the inside of the fuel tank and didn't pick up any rust or debris, but I wonder if I should just remove the tank and clean it anyway. The main jet and emulsion tube look clean and clear. The intake elbow looks new with the carb and the rubber is still soft/pliable. I'll re-inspect the vacuum lines. Basically, anything connected directly to the carb is new. It doesn't have separate o-rings on the carb connected to the elbow, it has a metal clamp that's tightened with a screw.
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timwhite74
Scoot Junior
Posts: 16
Location: Las Vegas, NV
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Post by timwhite74 on Aug 6, 2023 14:34:43 GMT -5
GrumpyUnk and classacted , I don't know if this makes a difference, but the float needle does NOT have a rubber tip and there's no rubber o-ring where the needle tip seats. just thought i'd throw that out there.
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Post by classacted on Aug 6, 2023 17:06:40 GMT -5
well, you checked the float valve and it seals like it's supposed to, but it's strange that it's not rubber (the tip). I've never seen one that wasn't.
I'm glad GrumpyUnk mentioned that intake manifold leak because I had one of those. the crack was almost completely covered by the clamp. the carb cleaner spray trick found it. the intake is prone to crack there because it has to flex.
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