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Post by tankmotor on Mar 28, 2015 21:24:12 GMT -5
This is my first forum post so go easy on me haha. I recently purchased my first scooter, a tank urban sporty 49cc. The dealer I bought it from put a big bore kit on it. Recently I've been having some hard starting issues so I tore the carb apart and found the pilot jet to be plugged. Everything else looked great so I bought a rebuild kit and a 40 pilot jet , a 75 main jet, and a 100 main jet to go along with it. I know that the original pilot jet was a 30 however I don't know what size the main jet was. I reinstalled the carb with the 40 pilot and the 100 main. The only way I could get it to idle some what decent was with the mixture screw turned all the way in. I took the 40 pilot out and installed the 30 and it seems to idle pretty decently. I test drove the scooter and I am still having problems on even the slightest hill where it doesn't pick up speed very quickly and it takes awhile for rpms to wind up. I wanted to see what happens and I noticed virtually no change. is this normal? I have an aftermarket air filter on it as well. Sorry for the long post. Any help would be appreciated.
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Post by niz76 on Mar 28, 2015 21:49:48 GMT -5
WELCOME!!!
Hi Tank. It seems you're on the right track but I'm thinking the monkey wrench in everything here is that aftermarket filter. I"ve done a handful of BBK's on 2t's and 4t's and never needed to change the idle jet. I was running a 91 Main Jet on the 4t BBK and it ran well so the 100 MJ you have seems to be in the ballpark. Now add the performance filter and that changes everything... Now you're pulling way more air in than the stock air box and need to jet the carb accordingly to get the air/fuel mixture in harmony again. In my experience the aftermarket air filters take a significantly larger jet than stock and don't really add any "performance" unless you're running a really high end race setup. If you run the stock idle jet (pilot jet) and the 100 MJ with the stock airbox I'd bet you'd be pretty close to the right tune- with that aftermarket filter however, you'd need to get yourself a handful of MJ's and start tuning based on feel of performance and reading the plug etc...
Again, this is all based on my opinion and previous experiences- hope it helps!
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Post by tankmotor on Mar 28, 2015 21:57:38 GMT -5
I have the stock air filter that I supposed to fit but the tube that hooks up to the carb almost seems too small. I just find it odd I didn't notice any difference between the 75mj and the 100mj. Any Ideas on that?
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Post by Fox on Mar 28, 2015 23:16:40 GMT -5
 How long it has been since the last valve adjustment? It's an important service procedure that should be done regularly to ensure optimum performance and it could be the source of your hard starting and general lack of power. I've run into the issue of the air filter tube not wanting to slip onto the carb many times. I heat the end of the tube with a blow dryer till it gets really hot and malleable and then it will stretch without tearing. Then I put it onto the carb while it's still hot. |
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Post by tankmotor on Mar 28, 2015 23:34:08 GMT -5
I adjusted the valves about a month ago. I set them to 3 thousandths.
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Post by Fox on Mar 28, 2015 23:53:19 GMT -5
Well might be worth another look to see if one tightened up on you.
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Post by tankmotor on Mar 29, 2015 0:05:37 GMT -5
I am new to scooters what should I expect out of it with a big bore kit for speed and acceleration? I am a big guy (225lbs).
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Post by tankmotor on Mar 29, 2015 13:04:22 GMT -5
I rechecked the valves and those were set right. I had the 100mj in and I reinstalled the stock air box. It seemed to idle ok but as soon as I would crack the throttle it would sputter. When I shut it off I saw white smoke coming from the tail pipe. I'm guess that it is running too rich. Should I try to adjust my jets to tailor the stock air box or keep goin up with my aftermarket filter? I didn't notice any change between the 75mj and the 100mj with the aftermarket air filter
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