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Post by banditsc on Dec 7, 2008 13:14:58 GMT -5
I just picked up a 2004 Schwinn Collegiate 50cc. It was running when I bought it, but not running after the ride home in my truck. It had good spark and everything, but wouldn't fire. I left it for the night and came back the next day and it reluctantly fired up, but it dies out under throttle when under load. If let it idle along it fine, but apply some throttle it will either bog down, or rev fine for a minute then die out.
It has a new carb that the previous owner had put on recently, and I just pulled it off and cleaned it out and put a new filter on. That didn't seem to do anything for me. The air box is also detached right now, so it should have enough air. I have a new Iridium plug on the way, but the old one seems ok, it at least has a nice spark to it.
So what else could be causing this problem?
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Post by Enviromoto on Dec 7, 2008 13:31:59 GMT -5
You need to do a valve adjustment.
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Post by Enviromoto on Dec 7, 2008 13:33:05 GMT -5
Valve adjustment on a 139QMB 50cc 4 stroke scooter motor. Now you will need access to the engine bay for me the easiest way to do this is to remove the seat bucket. But everyone has their own way and there is many different configurations of Roketas so what your looking to do first is to have access to the top of the motor. After you get the valve cover removed with 8mm socket or wrench you will need to follow these steps. Step 1. Set the engine to Top Dead Center (TDC) On your flywheel you will see some marks make sure you T on the flywheel lines up the the timing tab. Also check your camshaft and make sure your timing marks on the cam line up with the top of the head. Also you want to make sure that you are setting the engine at TDC on compression stroke. The T that lines up with the timing tab after the intake valve closes. After that is a simple matter of using a standard feeler gauge and set the valve lash at .004 for both the intake and exhaust valves. How do you do that you ask. Its simple really just take your 9mm wrench and loosen the locking nut on the valve tappet. Then you loosen the tappet until you can get your feeler gauge between the tappet and the valve stem. You want to tighten the tappet down on the feeler gauge but not to tight but not to loose. You want to be able to pull the feeler gauge out but there should be light resistance. Then you use a pair of needle nose pliers to hold the head of the tappet so it dosent move and tighten down the locking nut. Then repeat on the other side and put the valve cover back on. Once you get the motor back together you want to start it up and make sure you fixed the problem and listen for excessive tapping from the valves. A tick is ok a loud tap is a problem. If it sounds weird start back at step one and try again.
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Post by harrywr2 on Dec 7, 2008 13:37:07 GMT -5
The air box is also detached right now, so it should have enough air. You may have too much air...bogging at 1/4 throttle is frequently a 'lean bog' which can be 'not enough fuel' or 'too much air'. I'll also echo enviromoto...a valve adjustment would be a good idea as well.
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Post by banditsc on Dec 7, 2008 15:04:30 GMT -5
Well I did the valve adjustment and it's running much better now.. It's actually hitting 40mph. It is bogging a little when I got to full throttle though, if I back off a little it's fine. I'll put the air box on and see what it does. It's still in a disassembled state, I need to figure out how all those plastic body panels and what not go back on now. On a side note, does anyone have a link or place to order body parts for this scooter? I have a small panel missing from the top of the right rear fairing. Thanks.
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Post by banditsc on Dec 8, 2008 9:08:48 GMT -5
Putting the airbox back on seems to have fixed the WOT bog. It was dieing out on take off, but I'm hopping that was just being cold. I did loose 5mph on the top end though. I'm going to put on a Uni filter and try a 95 jet in it.
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Post by earlwb on Dec 8, 2008 11:19:05 GMT -5
The engines come from the factory set to run really lean. Borderline too lean. Anything that contributes to allowing more air in makes them run too lean. Going to a larger main jet should help.
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Post by Enviromoto on Dec 8, 2008 13:00:50 GMT -5
Putting the airbox back on seems to have fixed the WOT bog. It was dieing out on take off, but I'm hopping that was just being cold. I did loose 5mph on the top end though. I'm going to put on a Uni filter and try a 95 jet in it. I wouldnt recommend anything larger than a #90 MAIN.
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Post by banditsc on Dec 8, 2008 13:43:53 GMT -5
I wouldnt recommend anything larger than a #90 MAIN. Where would one find one of that size? I order the 95 from ScooterTronics, it's the smallest one they sell and there recommended size.
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Post by Troll on Dec 8, 2008 15:01:36 GMT -5
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Post by banditsc on Dec 8, 2008 15:26:38 GMT -5
Thanks, I see they have them. So is 50 the recommended or the 48? I guess I should check what's in there now. Is increasing the pilot jet recommended also?
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Post by Troll on Dec 8, 2008 15:36:11 GMT -5
No don't mess with that unless you plan a big bore kit like the 72cc. I started with an 88 main and went up to a 90 for the fact I had a mean backfire after i gutted my pipe. If your gonna get a UNI I'd use an 88 main.
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Post by banditsc on Dec 8, 2008 15:52:12 GMT -5
Thanks, I just checked and the current main jet doesn't have any marking on it, so not sure what's in there now. I guess I will go with a 88 jet.
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Post by Enviromoto on Dec 8, 2008 17:05:37 GMT -5
Thanks for the work guys. It will ship out tomorrow.
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Post by Troll on Dec 9, 2008 10:08:43 GMT -5
Anytime
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