cant reach top speed/bogging down

[T3hFantom]

for the past few weeks i have not been able to give my bike more than 1/4 throttle and it will only go about 15 mph. i checked the mixture and the plug was a nice brown color. at low end the bike has a lot of power till i reach the end of the 1/4 throttle and then it starts missing and making a popping sound out the muffler. but when i do not have the clutch engaged i can rev the engine up to WOT with out any bogging out...

another problem that has started to show up is after i run the engine at max 1/4 throttle stop at a stop sign and try to get back up to speed. i will have to open and close the choke just so that it will build up RPMs again. right now i ride the bike in 20 degree weather with a 25:1 fuel to oil mix with a CNS carb on a skyhawk 50cc. im well past break in on my fourth to sixth tank of gas. dont know if the cold has anything to do with it, but this bogging down at higher throttle settings has always been a problem even at warmer temps. though before it got really cold i was able to get the bike up to around 20 mph.

is my higher throttle settings causing the engine to run to rich? but

 

[motorpsycho]

the problem you are describing, sounds like the air-fuel mixture is too lean to me.
bogging, low power at w.o.t. and popping are usually the results of the air-fuel mixture being too lean.
beleive it or not, the weather can have a strong effect on the air-fuel ratio. an engine that runs good when it's warm out, may run too lean when it's cold out. this is because the cold air is a lot more dense than warm air.
The reason that you have to put the choke on to take off could be because it's too lean, but putting the choke on, you are reducing the amount of air that is being sucked into the carb, which is richening up the mixture. if it was doing this in warm weather too, then i would guess that your fuel-air ratio is way too lean. you may have to re-jet the carb, or you could have an air leak somewhere.
this is just my guess based on the description you gave, and i may not be 100% correct in my guess.

you could try lowering the "E" clip in the needle in the carb, which will raise the needle, giving you a richer mixture, but this will have no effect on w.o.t. performance.
if the bog and stuff is going on at w.o.t. you will probably have to re-jet the carb.
I had to re-jet the carb on one of my engines (80 c.c. 2 stroke, n.t. carb, modified exhaust and high flow air filter).
I also have a 50 c.c. 2 stroke,(expansion chamber and high flow air filter) and it's the version that does not have an intake tube (the carb is bolted right to the cylinder) and the only thing i had to do to it was lower the "e" clip one notch from the center. (raising the needle) i did not have to re-jet it.

 

[goodtime65]

It sounds like you probably have a fuel restriction somewhere.

 

[T3hFantom]

The bogging down happens at anything greater than 1/4 throttle. And I have the jet set on the second lowest setting on the jet. Ill adjust the jet and see how that works. If I need to rejet the carb where can I get the jets at

 

[motorpsycho]

sickbikeparts (look to the left for their link) sells delorto jets in various sizes. they fit the n.t. carbs, but i think the pitch of the threads is a tiny bit different. they will work, but they are tight when screwing them into the carb.
this was my experience anyway, and no, i didn't cross thread the jets. I tried several and they all screwed into the carb tight(not easy to screw in is what i mean). this did not mess up the threads in the carb or on the jets that i tried.
I ended up putting a .74 jet in my 80 c.c. to make it run right.....and it runs so much better now than it did with the stock jet (which i think was a .70)
someone once said that these carbs are jetted specifically for the 50 c.c. engines, and since you have a 50 c.c., you may not have to go to a much bigger jet. an increase of 1-2 jet sizes makes a huge difference.