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Post by gotbaja on Aug 12, 2012 0:47:13 GMT -5
Hello!  im new to the scooter world. i have a 2012 Jonway Thunder with the 139QMB engine. I have 400miles on it, have done scheduled oil change and changed that awful plug to an NGK. I really wanna get a new exhaust for the better sound. I know i would have to rejet in order to see any power increase. My question is, do i have to rejet the carb in order for my scooter to not run dangerously lean or lose power? I live in Albuquerque New Mexico, with an elevation of 5312 feet above sea level. I beleive these scooters are jetted to run at sea level. So could i SAFELY and WITHOUT LOSING POWER run a new exhaust on my scooter without rejetting? i was looking at this one www.ebay.com/itm/EXHAUST-SYSTEM-Performance-GY6-50-139QMB-Jonway-Lance-Longbo-Roketa-Sunl-/150760168270?pt=Other_Vehicle_Parts&hash=item231a019b4e&vxp=mtr |
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Post by reveeen on Aug 12, 2012 5:10:48 GMT -5
As far as I am concerned these things are jetted leaner than they should be, right from new, to meet emissions.
So, in all likelihood, you could pick up a bit of power with some richer jetting, with, or without, the exhaust.
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Post by gotbaja on Aug 12, 2012 10:50:45 GMT -5
so my question is if i were to put this exhaust on now with the stock jetting would it lean it out to much or make it run like crap?
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Post by 90GTVert on Aug 12, 2012 12:12:36 GMT -5
:welcome:
Hard to know since they aren't all created equal. May run alright. May run lean, but well, and overheat. May be so lean it runs like crap. Only proper way to do it is to pick up a selection of jets and see what you need to do after it's installed. It's safest to assume it will be lean and install a larger jet if you don't wish to tune. At least if it runs bad from being rich it's not as likely to damage anything.
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Post by usmcdoc on Aug 12, 2012 13:56:13 GMT -5
Hello! im new to the scooter world. i have a 2012 Jonway Thunder with the 139QMB engine. I have 400miles on it, have done scheduled oil change and changed that awful plug to an NGK. I really wanna get a new exhaust for the better sound. I know i would have to rejet in order to see any power increase. My question is, do i have to rejet the carb in order for my scooter to not run dangerously lean or lose power? I live in Albuquerque New Mexico, with an elevation of 5312 feet above sea level. I beleive these scooters are jetted to run at sea level. So could i SAFELY and WITHOUT LOSING POWER run a new exhaust on my scooter without rejetting? i was looking at this one www.ebay.com/itm/EXHAUST-SYSTEM-Performance-GY6-50-139QMB-Jonway-Lance-Longbo-Roketa-Sunl-/150760168270?pt=Other_Vehicle_Parts&hash=item231a019b4e&vxp=mtrMy girlfriends scooter that same exact exhaust. Sounds nice...she got about 5 mph gain. They sell the same one ones on Ebay fo 79 bux. HOWEVER you WILL need to make a support bracket for muffler itself..or vibration will crack the pipe off. Here is a pic of how I make hers...3 bux in angle aluminum from Menards....30 mins labor and so far it has lasted almost 3 years... Btw she painted hers black...they say they are gold...but they are NOT...there are metal flake orange. Anyway check out pic and see how to make the mounting bracket. Also as stated above...they come jetted WAY lean to pass emissions...so lean in fact I have seen many 2 stroke engines soft seize...and 4strokes overheat till they ruin the piston and rings..  Attachments:
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Post by usmcdoc on Aug 12, 2012 14:13:14 GMT -5
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Post by stepthrutuner on Aug 12, 2012 14:31:42 GMT -5
If it's adjustable I'd try raising the needle a notch before any jetting changes. With your altitude your factory jetting may not be so lean.
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Post by gotbaja on Aug 12, 2012 14:58:44 GMT -5
well heres something to add.. i took off the small cap on the end of my stock airbox (the one with the mesh and screws) today and tried to run it... ran like total crap. would get over 15 and was hesitating like crazy. So this is making me think that the exhaust will lean it out...? are my thoughts justifiable? i do not know how the stock air box works... if it loses suction or vaccum if u take the cap off... but i def do not want to crack a piston or overheat. Not sure if it was running too lean or rich with the cap off... but this makes me think that i should just wait till i can afford (time wise) to to a full rejet and then do a new filter as well. The odd thing is is that when i give it a quick rev sometimes i feel a slight hesitation, like its getting too much fuel... not sure. also any opinions on aftermarket plug wires? just as a side topic.
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Post by xxxSmokeKUSH420alldayxxx on Aug 12, 2012 15:18:07 GMT -5
I recommend a high flow air filter and #88 main jet combo from scrappy dawg scooters. Im currently running the setup with my exhaust and it runs excellent.
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noday
Scoot Enthusiast
Posts: 149
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Post by noday on Aug 12, 2012 15:28:35 GMT -5
I detect a fear of changing the jets. it is not a big deal.
It is a regular and ordinary part of tuning a scooter.
changing: plug wires, cdis, racing coils, etc..... all increase the reliability of combustion.
in general, they make the engine "run" better but have no significant effect on top end speed
small single cylinder engines need a close balance between intake air flow and fuel to operate properly
more air + more fuel = more power
power does not = speed as in a fixed gear engine
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Post by gotbaja on Aug 12, 2012 16:27:41 GMT -5
I detect a fear of changing the jets. it is not a big deal. It is a regular and ordinary part of tuning a scooter. changing: plug wires, cdis, racing coils, etc..... all increase the reliability of combustion. in general, they make the engine "run" better but have no significant effect on top end speed small single cylinder engines need a close balance between intake air flow and fuel to operate properly more air + more fuel = more power power does not = speed as in a fixed gear engine yes i will admit i am a bit afraid of a rejet lol mostly because i just dont want to ruin my scooter. im not new to the tuning world, just with mopeds and small engines in general. ive worked on my subaru for a long time and my (sold) 66 mustang with a 30/289 hybrid build. so im in the learning process when it comes to this new 49.5cc engine. Thank you for all the great help! heres a few more noob questions... 1. What are some mods to increase my top speed? i know changing the roller weights will help, but i already struggle with climbing hills as i am 5'11" 230lbs. what about a whole new variator and/or clutch? if so what are some good brands? ive seen ruckus's with the NCY variator hit like 38 completely stock. So far the only one i can find is from Scooter Parts Express. 2. Windscreen: Increase top speed or increase drag? ive heard mixed reviews. I already have a rather areodynamic scooter and a wear a full face helmet. 3. De-restriction. I have no pink wire on my cdi (onjly 5 wires). i have not checked my variator for the "wedding ring" or the top of my carb for the screw. Any tips on this? thank u for all the help again :sos: |
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Post by xxxSmokeKUSH420alldayxxx on Aug 12, 2012 18:20:00 GMT -5
Keep in mind a stock 50cc piston is about the size of a golfball lol.
Ive had good luck with a
ngk plug
racing cdi
racing coil
Airfilter with #88 main jet
These mods are extremely easy and made my scooter fast im 6ft 200lbs
I would stay away from rollers, they just wind your engine out basically
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Post by xxxSmokeKUSH420alldayxxx on Aug 12, 2012 18:22:05 GMT -5
Oh and too answer your question you MUST rejet with a pipe, If not you will run lean, the engine will stumble, the plug will turn white, and you could damage your piston (Thats how i killed my tao tao)
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Post by stepthrutuner on Aug 12, 2012 18:39:36 GMT -5
Every thing you need to know about cracking open the carb, etc., etc. is right here in the tech section. Hope your carb is not a sealed one....
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Post by xxxSmokeKUSH420alldayxxx on Aug 12, 2012 18:52:42 GMT -5
Yeah if your carb is sealed put it aside and buy a brand new carb on ebay for 30$ and build that carb, You can allways revert back to stock then
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im new to the scooter world. i have a 2012 Jonway Thunder with the 139QMB engine. I have 400miles on it, have done scheduled oil change and changed that awful plug to an NGK. I really wanna get a new exhaust for the better sound. I know i would have to rejet in order to see any power increase. My question is, do i have to rejet the carb in order for my scooter to not run dangerously lean or lose power? I live in Albuquerque New Mexico, with an elevation of 5312 feet above sea level. I beleive these scooters are jetted to run at sea level. So could i SAFELY and WITHOUT LOSING POWER run a new exhaust on my scooter without rejetting? i was looking at this one
