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139qmb
Aug 19, 2018 8:46:06 GMT -5
via mobile
Post by KSR Moto on Aug 19, 2018 8:46:06 GMT -5
Scoot is going very slow around 20mph and after some time it just "wakes up" and starts riding normal (around 35mph) scoot is all stock
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139qmb
Aug 19, 2018 10:23:42 GMT -5
Post by GrumpyUnk on Aug 19, 2018 10:23:42 GMT -5
First thing I would check is the fuel supply. Limit the fuel and you'll limit the engine rpm. A sticky float could be staying closed, and allowing the float bowl to have a too-low level of fuel. Could also be chunks of dirt that flow/block/flow. tom
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139qmb
Aug 19, 2018 12:44:25 GMT -5
Post by diynuke on Aug 19, 2018 12:44:25 GMT -5
Scoot is going very slow around 20mph and after some time it just "wakes up" and starts riding normal (around 35mph) scoot is all stock Could indicate very rich choke so could be a clogged air filter but this shouldn't be common. after some the choke shuts of and that could be the reason why it starts running good again. So just check the usual stuff. If you have tools for it check the valve lash have clean oil in it. check for good fuel flow from the tank. have a look at the spark plug. it should be a bit coffee brownish color. if its black or white It is a wrong main jet or something is wrong with the air filter. But first I would just take the spark plug out and have a look and if you aren't sure just post a picture
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139qmb
Aug 19, 2018 15:19:43 GMT -5
via mobile
Post by KSR Moto on Aug 19, 2018 15:19:43 GMT -5
Scoot is going very slow around 20mph and after some time it just "wakes up" and starts riding normal (around 35mph) scoot is all stock Could indicate very rich choke so could be a clogged air filter but this shouldn't be common. after some the choke shuts of and that could be the reason why it starts running good again. So just check the usual stuff. If you have tools for it check the valve lash have clean oil in it. check for good fuel flow from the tank. have a look at the spark plug. it should be a bit coffee brownish color. if its black or white It is a wrong main jet or something is wrong with the air filter. But first I would just take the spark plug out and have a look and if you aren't sure just post a picture Here is the picture of the spark plug
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139qmb
Aug 28, 2018 11:34:54 GMT -5
Post by diynuke on Aug 28, 2018 11:34:54 GMT -5
As far as i see it now it wouldnt hurt going a jet smaller. looks a bit rich and how old is the sparkplug.? and personally i would just get one of those mainjet kits and try going a few sizes up or down and see how the scoot reacts to it.
on allot of stock 139QMB engines jet 80 is installed which allot of times is around the right size but yeah that also depends on the air filter
This is what i think: as the engine warm's up the engine gets hotter so the air entering the engine less compact which would mean it goes leaner when it's hot so that says a leaner jet
so a too rich jet with the choke could be the reason why it bogs when its cold/the choke is activated (check the airfilter first tho.
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wahlman
Scoot Enthusiast
Posts: 111
Location: Miami, Florida
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139qmb
Aug 28, 2018 18:03:45 GMT -5
Post by wahlman on Aug 28, 2018 18:03:45 GMT -5
This is so cool, I am certainly impressed with the wisdom on this forum. O.P. just stated his symptoms and we have all these gear-heads willing to chime in and give advice for free.
I really respect you guys not just for your knowledge and wisdom but also for your kindness to render help to a complete stranger and not charging any money.
This is really Humanity at its finest. Good Samaritans....you guys are really great people. My hat goes off to you
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139qmb
Aug 29, 2018 23:27:22 GMT -5
via mobile
Post by kagetenshi on Aug 29, 2018 23:27:22 GMT -5
If it is a stock 50cc with the stock carb (usually either 17mm or 18mm from what I gather), I would assume a #72-#83 main jet should suffice depending on air flow restrictions. Though this is at best a ballpark estimation to use as a start. Jet kits are fairly reasonably priced.
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ratdog
Scoot Enthusiast
Posts: 342
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139qmb
Sept 1, 2018 9:43:34 GMT -5
Post by ratdog on Sept 1, 2018 9:43:34 GMT -5
Wait! That plug is NOT rich. That plug is very lean. On a correctly jetted bike, the “white part” ( insulator) should be tan. There is something else you might want to check. These little guys have a “automatic” petcock. What it really is is a vacuumoperated petcock. Trace the fuel line back to the gas tank and you will see one or two other lines back to The petcock. There normally is a lot of extra tubing there. If there is a lot of extra, I would pull the tubing off, cut about an inch and a half off and put it back on. Here is something to try regarding the petcock. Take the fuel one off at the carb and put it in a jar or something to catch the gas. A very little gas should run out. Now turn on the ignition and crank the starter. When the engine starts cranking, there should be a sudden flow of gas. If you just get a trickle, I would look to those lines that go to the petcock! Ofcourse, a clogged fuel filter would also cause this to trickle, but a clogged fuel filter wouldn’t get better when the engine gets warm. The other thing to check would be the electric choke. Easy to do, start the bike up cold, unplug the electric choke. If the bike stumbles and most likely stalls when it is in plugged, you are good. If there is no difference, then you have a bad electric choke
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