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Post by Silar on Apr 18, 2015 9:26:07 GMT -5
I just recently bought a used Chinese scooter. It's got the GY6 139QMB 55cc engine. At idle it sounds fantastic. I can rev it and sounds great up to max RPM. I've been working on this scooter for the past week or so since it needed some things done to it. I have another thread in the Builds section under Transformer Bumblebee.
Still working on some lighting issues, but today I thought I'll take it down the road just to see how it does. I didn't have the instrument panel connected so not sure what RPM's I got at, but at WOT I maybe got up to 20mph and was even slower going up a slight hill. RPM's didn't sound like it got over 4-5k.
It does still have the original belt on it and I definitely need to buy a new one which I am today, but would this be causing my issue? I figured I'd still hear the RPM's go up high but the scooter would be slow. It doesn't sound bogged or anything when riding.
There's absolutely no smoke and it sounds great... Just not getting the speed I expected..
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WHAT FIXED IT
The vacuum operated fuel petcock was apparently faulty causing it to suck gas into the intake through the vacuum line. This was causing an overly rich condition that was bogging the scooter down like crazy.
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Post by Silar on Apr 18, 2015 13:03:41 GMT -5
Anyone.. Bueller?.. Bueller?..
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Post by Upgrayedd on Apr 18, 2015 16:58:05 GMT -5
greetings. among other things, perhaps it is 'upshifting' early and keeping the engine at a lower rpm. i dont think a belt alone would cause that. perhaps some lighter roller weights would help bring up the rpms?
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Post by Silar on Apr 18, 2015 17:34:22 GMT -5
greetings. among other things, perhaps it is 'upshifting' early and keeping the engine at a lower rpm. i dont think a belt alone would cause that. perhaps some lighter roller weights would help bring up the rpms? It's almost like when the scooter is under load, it just doesn't get up RPM's but idling on the center stand, I can rev it and it goes up to 8k-9k with no problem. I just put a new carb in last night, but today was the first time I've even tried to ride the scooter. Could the carb not be adjusted properly and cause this? I'm just not very familiar with scooters, but have quite a bit of experience on auto and motorcycle engines. This whole belt/variator/clutch/etc stuff is kicking my butt.. |
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Post by vanillagorilla on Apr 18, 2015 17:34:33 GMT -5
Same thing happened to me, I got the same scoot used for my wife and man it was slow I cleaned the carb with motorcycle carb jet cleaners changed plug coil cdi and all that sucker would pull was 23 mph on flat I did the proper valve adjustment and she does a solid 41.26 mph gps verified all stock and she loves the Speedo goes to about 6 o clock thats a chinameter for ya
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Post by Silar on Apr 18, 2015 17:42:08 GMT -5
Same thing happened to me, I got the same scoot used for my wife and man it was slow I cleaned the carb with motorcycle carb jet cleaners changed plug coil cdi and all that sucker would pull was 23 mph on flat I did the proper valve adjustment and she does a solid 41.26 mph gps verified all stock and she loves the Speedo goes to about 6 o clock thats a chinameter for ya Are you serious!?!?! I've not adjusted the valves yet. I never would have thought that would be something to check. I also changed the plug and coil. I've not changed the CDI yet.. I'll let her cool down and try adjusting the valves. BTW.. What did you adjust your valves to? |
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Post by vanillagorilla on Apr 18, 2015 17:58:30 GMT -5
Both at .004 on top dead center there are vids in the tech section if you need a few guide's
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Post by Silar on Apr 18, 2015 18:10:37 GMT -5
Both at .004 on top dead center there are vids in the tech section if you need a few guide's Thanks. I've already watched a few vids last week on it so shouldn't have any issues... |
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Post by Upgrayedd on Apr 18, 2015 18:20:05 GMT -5
greetings. among other things, perhaps it is 'upshifting' early and keeping the engine at a lower rpm. i dont think a belt alone would cause that. perhaps some lighter roller weights would help bring up the rpms? It's almost like when the scooter is under load, it just doesn't get up RPM's but idling on the center stand, I can rev it and it goes up to 8k-9k with no problem. I just put a new carb in last night, but today was the first time I've even tried to ride the scooter. Could the carb not be adjusted properly and cause this? I'm just not very familiar with scooters, but have quite a bit of experience on auto and motorcycle engines. This whole belt/variator/clutch/etc stuff is kicking my butt.. yep yep tuning the carb can help to get it better. stick around - there's lots of good info here and good people. the best way i know how to explain the cvt is it sort of works like a bicycle shifting. the belt will ride higher in the back when you start out, and ride real low in the front pulley at start. then as you get going faster and faster, the belt shifts, and pulls out higher in the front pulley, and drops lower in the rear pulley. its really a pretty neat setup. the two pulleys essentially pull against each other, max power is somewhere around 7500rpm, so if your cvt is shifting to final gear really early and dropping the rpms to around 4-5k, it may not be able to go as fast as if it were to shift up around that max hp mark of 7.5k, where you would have more useable power. the rear pulley has a big spring in the middle of it, and the front pulley has small roller weights in it that push out more as the engine ramps up. those roller weights are what you may could change out if need be, to a lighter weight. |
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Post by Upgrayedd on Apr 18, 2015 18:21:11 GMT -5
valve adjustment may help a lot, especially if they are out of adjustment. that is something to check out while tuning up, before considering lighter weights. good thought.
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Post by Silar on Apr 18, 2015 18:59:12 GMT -5
valve adjustment may help a lot, especially if they are out of adjustment. that is something to check out while tuning up, before considering lighter weights. good thought. I just adjusted the valves to .004 for both and still same problem, except now I've got valve tapping noise coming from them. I've seen somewhere where they should be set to .002 for the intake, and .003 for the exhaust. Not really sure about that though.. Dumb question.. If it's not the carb (I've triple checked it and even adjusted the needle to go rich to lean), or the valves, and if I get this belt next week and still have the same issues, what else could it be? I did take the belt off and put it back on so I could inspect it. When I did, I noticed that it required a lot of force to open the variable pulley on the back to slip in the belt. The springs are strong. The belt definitely needs replaced, looks worn, but isn't frayed or anything like that. The rear transmission system seems to run smooth when turning by hand. Could the clutch need some kind of adjustment also? Could the clutch not be engaging? I'm going to have to research the slides, clutch, tranny, etc.. |
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Post by Silar on Apr 18, 2015 19:09:28 GMT -5
One other note. I've noticed that on takeoff it seems good, but once rolling, anything over about a quarter turn of the throttle doesn't seem to give it anymore RPM's or power. Starting to make me think it is the clutch or the tranny. Engine sounds good, just no power. Even WOT after takeoff it just doesn't give it any more.
Where's 99GTVert when you need him! lol..
Dumb question, but is the timing adjustable at all?
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Post by Upgrayedd on Apr 18, 2015 19:53:56 GMT -5
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Post by Silar on Apr 18, 2015 20:57:43 GMT -5
I appreciate the video, but what would you suggest?
Seems like the clutch engages properly. I checked and this bike has rollers. May upgrade to sliders. I'm really just trying to get this thing back to factory so it runs right, then later this year maybe upgrade to a BBK, larger carb, etc..
At about 6:42 on the video, he talks about how he had removed the airbox restrictions and was running so lean that it was bogging down his bike at WOT. This is very much like what I am experiencing. I'm kinda wondering if I've got an air leak somewhere in the intake of the carb, or at the manifold...
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Post by Silar on Apr 18, 2015 23:59:52 GMT -5
I guess I'm assuming a lot since I bought this bike used and it wasn't in the best of conditions. This is a really dumb question but I've got to ask.. If the original roller weights are still in the scooter, wouldn't the weight be sufficient since that is what came stock, and if anything any wear on them would just make them lighter, wouldn't it? What are the stock weight of the rollers?
What's funny is this bike has less than 600 miles on it according to what is shown on the instrumentation, but who knows.
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