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Motorized Bicycle Trouble Shooting Use this area to post problems that may arise, if you could use some help in figuring out what is wrong with your engine and what needs to be done to achieve top performance.

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Old 11-13-2016, 01:58 PM
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Chaz Chaz is offline
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Default Up against a wall

I have an older pk80 with over 1000 miles on it. Moderately ported. Free flow exhaust, and NT speed carb with stock jet. The needle clip is in the leanest slot. I drilled a bunch of holes in the air filter cover so I believe it is breathing ok for the intake. Plug colour is okay if anything a bit on the rich side. 26 inch wheels with the 44 tooth. Upgraded plug wire and socket with ngk b6

I have been having trouble getting the rpm past a wall. Sorry, no tach reading. I'm getting some 4 stroking in low to mid rpms/speed. As I reach about 25 mph it sort of feels like bogging or is it 4 stroking? I'm not sure. The fuel flow seems adequate.

When the rain stops I will test again but it seems like the bike would rev up to higher rpm if I turn off the gas at the tank and burn off the gas in the carb bowl.

In the summer I was able to rev up to reach 30 plus mph and, as a side note, the engine actually smooths out at higher rpm

I suspect I will have to jet smaller but looking for confirmation of this.

Does anyone know what my problem is?

thanks, Chaz
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Last edited by Chaz; 11-13-2016 at 02:04 PM.
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Old 11-13-2016, 05:53 PM
crassius crassius is offline
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Default Re: Up against a wall

usually, first thing to do is check for oil residue around gasket and seals, then check float level, also check that mounts are tight
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Old 11-13-2016, 06:35 PM
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Chaz Chaz is offline
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Default Re: Up against a wall

Thanks, crassius, the seals and gaskets are fine and float level good and my nuts are tight.

Might actually get some sunshine tomorrow so I'll fiddle

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Old 11-13-2016, 10:29 PM
crassius crassius is offline
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Default Re: Up against a wall

I just started testing on my new pk80 kits and find the longer stroke does smooth out at higher revs (pulls hills better at low speed tho) - did you try loosening your muffler to see if that helps?
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Old 11-13-2016, 11:52 PM
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Chaz Chaz is offline
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Default Re: Up against a wall

No, I didn't yet since I was convinced that it's breathing well but you are right, I need to test it.
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Old 11-14-2016, 08:33 AM
curtisfox curtisfox is online now
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Default Re: Up against a wall

if I turn off the gas at the tank and burn off the gas in the carb bowl.
Good sign that it is running to rich, as it runs out of gas it leans and revs higher. Take the air cleaner of and see how it runs. Like Crassius said do some testing before changing jet..........Curt
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Old 11-14-2016, 12:27 PM
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Chaz Chaz is offline
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Default Re: Up against a wall

Thanks for the advice, Curt, I will do some testing and post any results.
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