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Post by natetheokay on May 20, 2013 12:10:06 GMT -5
I've got a 50cc 4T (qmb139) that I recently replaced the air filter/box on (as well as the shock absorber, coil, valve adjustment, and more). It ran fine for the first 2 days, but then after I started the scoot, it died if I opened the throttle at all.
I took it apart and found that the vent spigot on the valve cover had popped off (there doesn't really seem to be anything holding the stupid thing in) so I reattached it.
Now, after warming up, the scooter will die if I open the throttle all the way (i.e. go from idle to WOT), but works fine if I open the throttle slowly from idle to WOT. Any idea how to get my poor little scoot back to top condition?
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Post by alleyoop on May 20, 2013 12:25:08 GMT -5
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Post by natetheokay on May 22, 2013 8:30:52 GMT -5
Okay, I followed the steps carefully and took my time, getting up to max RPMs and then adjusting the idle to just before the wheel spins (approx. 3000 rpms). That helped, but the engine still dies when opening up the throttle quickly. It also dies after idling a minute or two just after a cold start (i.e. after enricher closes), but will idle normally after giving a few minutes to warm further (accomplished by opening the throttle a little to give it more fuel).
Assuming the A/F mix screw on the carb itself is optimal, what do the above symptoms imply? Too much air, too little? Are the valves too tight (I adjusted them to the .06/.08 specs on VIN plate).
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Post by larry001964 on May 22, 2013 9:46:37 GMT -5
Hi Natetheokay,
I would check the airbox, and the rubber tube leading to the carb sometimes these come loose or completely off allowing too much air, this is a classic symptom of getting too much air,, It also could be a vacuum leak on your intake.. I would follow what Alleyoop says, but if that don't solve the problem then look where I suggested..
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Post by natetheokay on May 22, 2013 10:10:54 GMT -5
Thanks Larry, i'll give the hoses a good look over and see what I find.
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Post by alleyoop on May 22, 2013 10:35:19 GMT -5
If you open the throttle quick and it bogs, to much air not enough fuel.
Alleyoop
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Post by natetheokay on May 23, 2013 12:52:11 GMT -5
Okay, so I checked all my lines and made sure the air filter assembly was well sealed, no luck same symptoms. I took apart the carburetor and I noticed that there's no spring between the vacuum chamber cover and the diaphragm piston (there's one shown in the gy6 shop manual in the vacuum chamber breakdown section). Could this be the source of my problems (i.e. do all/most stock carbs have a spring between the cover and diaphragm)? Suggestions on where to get one, if needed?
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Post by larry001964 on May 23, 2013 17:12:14 GMT -5
Yea there's suppose to be a spring going from the cap to the bottom of the diaphragm, It rest on a clip that holds your needle down to the diaphragm as it raises and lowers the needle in and out of the main Jet.. Yea that would definitely explain why it's bogging..
Don't know where you can get just the spring.. Id just buy a new carb.. They are pretty cheap...
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Post by alleyoop on May 23, 2013 17:24:39 GMT -5
That is why it is getting to much air, without a spring the suction draws in air and because no spring it lifts the CYLINDER up right away as if it is at WOT. You need the spring in there or get a new CARB they run around $30.00. Alleyoop  |
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Post by geh3333 on May 23, 2013 17:36:13 GMT -5
I had that prob when my scoot was stock. I replaced the air filter and my scoot would bog at wot no matter how i adj it. I had to close off two of the three holes that were at the bottom of my air box for it to run right. It was obviously gettin to much air.
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Post by alleyoop on May 23, 2013 17:37:57 GMT -5
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Post by onewheeldrive on May 23, 2013 18:23:18 GMT -5
It ran fine for 2 days that way??
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Post by natetheokay on May 24, 2013 8:44:20 GMT -5
I found this carburetor spring, does it look like it fits the bill? At $2.50, i'm hoping so! eshop.mainelyscooters.com/151-179Otherwise I'll jump in with an all new carburetor. If that works, i'll have to look for a new way to break the scooter, seeing as how i've managed to damage just about everything with my amateur wrenching. |
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Post by natetheokay on May 26, 2013 17:00:38 GMT -5
Okay, got the spring in the mail yesterday and installed it today. Bogging issues seemed to have vanished. However, now even when I screw the A/F screw all the way in and the idle screw all the way out, I idle at about 3100. Prior to my spring install, 3100 was where I kept the RPMs, but I could lower it by adjusting AF and Idle screws.
Obviously, if it runs okay, i don't mind too much, but I still find it strange that I can't drop the RPMs any lower...
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Post by alleyoop on May 26, 2013 17:13:54 GMT -5
Let me ask The throttle cable handle Is there about 1/4 of an inch play before it pulls on actual the throttle cable inside the sheave? The throttle handle should have about 1/4 inch of play.
It maybe that it is already pulling on the cable which I think is the case. If so give it some slack lengthen it using the adjustment EITHER by the Bracket on the carb or by the handle it should have an adjustment on the cable itself.
Alleyoop
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..BAD TO THE BONE..
