66cc china, bogging

[Richluhring]

so my engine is bogging at any throttle position once it levels out. whether it is 1/4 to wot. I have replaced the plug and fuel it came on sudden. I have checked intake and exhaust port, tightened all bolts, cleaned the carb, exhaust pipe is clear. I run 32-1 fuel/oil, now when it starts if I let off the throttle and then twist it back up. it clears up. the plug is a perfect light brown. I have opened up the air cleaner by adding some hole. that helped a little. it has well over 600 miles on it. I have the fuel needle set to the top slot. that is where it runs best. I have checked the magneto,. it idles perfect and has power. it runs great until it reaches its top speed for the throttle position then it bogs/or four strokes. am not sure which it is. it does seem to not bog if I am going up a slight incline, but going on flat ground or slightly down hill to a lot down hill it Boggs a lot. HELP!! I HAVE TRIED ALL THAT I CAN..I AM LOST

 

[Slogger]

If it came on suddenly, and your fuel flow is good, and your carb jet is clean and the float needle and seat are clean, and you have fresh gas in the tank, take the side covers off and see if the magneto or drive gears on the other side are oily. It might have a leaking seal.
Hope you figure it out.

 

[Richluhring]

I checked in there.. clean and dry all else you mentioned is good to
im a auto mechanic by trade and this has me baffled. jug and piston are all good to.. it runs great.. just boggs when it flattens out at any given throttle position

 

[Slogger]

Maybe the muffler is clogging up?

 

[maniac57]

EDIT:
Nevermind. I just re-read your post and what you are describing is common four stroking.
Your needle is set full lean and it still does this, so you need a smaller main.
Every single stock chinadoll ever shipped across the pond was jetted so rich it blubbers like a bulldog eating mayo from the jar.
Most like two sizes or so smaller on the main but keep an eye on the plug.
I prefer to solder and re-drill my own since you can order ten jets of the same size and get fifteen different actual holes.
Remember to reset the needle full rich when dropping a main size, and watch that plug! Lean mixtures kill chinadolls so always take small steps.
I like to jet for max power and best cruise, then back off one slot on the needle for better lubrication.

Best four-stroking mod for my money is a properly jetted sha carb. Mine almost feels Japanese when you're riding.

 

[Richluhring]

muffler is clear, gas cap is good as well..it has power and wont bog like when going up a slight grade.. but on level ground and down grades it boggs/misses/fourstrokes

 

[Slogger]

Check the compression, it may need a top end job. I don't know the minimum you should see, someone here will know.
My bike would sag off like that before the rings were fully seated.
Maybe your rings are worn.

 

[fatdaddy]

Also, check yer intake for air leaks. The easy way to do this is to drizzle water on both ends of the intake, carb side and cyl. side, while the engine is at idle. If RPM's lower or it dies ya got a leak.
fatdaddy.

 

[maniac57]

I'm telling you, it's jetting. Plain and simple. The feeling you get when you gas it is the bog from the main being fully exposed and flowing too much fuel. At 3/4 throttle and under slight load it cleans back up because the needle tip is back in the jet restricting fuel.
Unless you have been inside that carb, it is jetted too rich. Absolutely guarantee it.
Try a smaller main. Trust me.

 

[Richluhring]

I'm telling you, it's jetting. Plain and simple. The feeling you get when you gas it is the bog from the main being fully exposed and flowing too much fuel. At 3/4 throttle and under slight load it cleans back up because the needle tip is back in the jet restricting fuel.
Unless you have been inside that carb, it is jetted too rich. Absolutely guarantee it.
Try a smaller main. Trust me.

so with over jetting it would run better when there is cold weather? that would explain a lot.. am at sea-level..what jet size you recommend

 

[Richluhring]

so what size is the jet needed for sea level?

 

[maniac57]

I can't recommend any one size. Go down one size from what you have now and test.
Cold weather would affect it since colder air = denser = more oxygen for too much fuel = runs better.
Remember to reset your needle when swapping the main. If you don't know what size you have now, find some wire gauge drillbits and find which fits the hole, then go down two drill sizes. (about one jet size)
China jet actual hole size has nothing whatsoever to do with whatever size is marked if any.
You order 5 jets of the same size, and you usually get six different holes.
Best way is to solder and re-drill them yourself for total fine control.

 

[Richluhring]

well I just ordered a 20 piece jet kit from gas bike. going from 60 to 80.. think thast will do it?.. thanks for the help

 

[Richluhring]

I ordered this kit

 

[Richluhring]

the kit in the pic is what I ordered

 

[Davezilla]

It should dial in at 2 to 3 sizes smaller than what you got in there now.... the stock jet isn't numbered but its said to be a 70.
Most of us here in Texas between sea level and about 1000 feet are doing great with a #66 or 65 jet. Leave the needle in the middle slot and check part throttle cruise, go down one notch if it 4 strokes at part throttle cruise and drop it to the lowest setting if it continues after you got it jetted right for full throttle. You can further fine tune the needle setting by buying some 4mm washers under the clip, these washers are sold at home depot and other places in either brass or aluminum and they are 1/2mm thick so they're great for when its too lean at one setting but too rich raising it just one notch. I use this to fine tune my motorcycles as well since many times it'll dial in best between the middlennotch and the first notch down so adding anwssher under the clip will let you use 1/2 notch increments.

 

[Davezilla]

Also if you modify the exhaust or intake for better flow you may need to jet up a size or 2 to compensate.

 

[Richluhring]

I have put a expansion chamber exhaust on it months ago, but that made it worse.. the pic on here as my avatar is my motor now