bog down at top speed

well it seems lately that im having a small issue with my top speed..everytime it gets to the top speed the motor will bog down a bit then resume. it will repeat the process over again..what could be causing this? im not even maxing out the throttle. thanks for any help its driving me nuts!

timeing off a little???
Check yur magneto (little black box that generates the spark) make sure its close but not touching the flywheel
could be a cloged jet but that is rare
what was it oh ya the keyway might be bent a small bit
try replaceing the little soft metal peice with another one (NEW ONLY don't use a used one) see if anything helps

maybe it wants more air and gas.

Check you motor mounts to be sure they are not loose, it can cause a small vibration that will cause a fuel delivery problem.

Be sure your fuel valve on the tank is flowing properly, could be the valve or the gas cap not venting properly. I'd start there and keep us posted.

At times, I've got the same issue. Aggravating to say the least.

Sometimes, she runs GREAT! But at other times, she'll hit 22 MPH, Bog down to 19, and then run back up to 22 again. What gives?

I have a newer build, with 120 some miles on it. At it's best, she's done a good 29 MPH. So what keeps changing here to give me different results on each ride?

The float bowl is not filling fast enough to keep up with the engines demand for fuel. fairracing31 has suggested several reasons this could be happening.

I was having the same problem as you guys are describing and the filter in the tank was clogged. I cleaned both the in tank and the in line filter and cut 1 1/2 inches off my fuel line and that really helped my motor scream. keep the fuel line as short as possible.

340 lbs at 33 mph / 80cc raw - 44 tooth

I had my bike acting up the other day and found the base gasket leaking just a little bit it would do strange things idle, them idle high, then idle back down.
bogging can be the main jet drilled too big. when its bogging try the choke start putting it on if it runs better then you know its not getting enough fuel.
Starving for fuel will also make it bog. Fuel filter? yea there is one on some, in the tank clogging off with crud. If your bike is like mine fill it up a little too much and you get fuel tracks on the tank then its not the cap not venting.
Float sticking or set so the level is too low and running out of fuel or sticking shut.
My guess is measure your main jet and see just what size it is and if it is a nice round hole or like some drilled with a hammer and a nail (hole oval shaped). You can fix that with the proper drill and solder. check out my link on the carb.
http://motorbicycling.com/f39/motorized-bicycle-carburetor-install-rebuild-302.html
Norman

I totally Removed the in tank screen/filter. Replaced it with an in line fuel filter that I can see fill up as I ride. This seems to have helped a bit, but I haven't been on a 5 to 10 mile road cruise yet after this change.

In the neighborhood, So far so good. I'm still not getting what I expected, but while I'm here more, I think I have the wrong gear on the rear wheel for the Ultimate Speed.

I have a 50 Sprocket. For Speed, I think I need a 44 or less sprocket. But for Torque and Power, I think I want the 50 Sprocket.
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Somewhat of a decision point here on my end, huh?

If you are still having problems on a longer ride, check the gas cap to make sure it is venting properly.

thanks for all the help guys! im sorry for the late response here, ha also after about 20 min of riding last night i notice that there were flames coming out of my exhaust! i have the baffle removed ofcoarse. it is pretty awesome but maybe that can help me determined the problem. im goin to take the bike apart later in the week to tune it up..

thank again.

Flames?!? That ain't good.

flames out of the exhaust are cool,but not good.

Bikeguy Joe said:

If you are still having problems on a longer ride, check the gas cap to make sure it is venting properly.

Click to expand...

Thank You, Joe. Will do on the next longer ride. (5-10 Miles, All Out)

If I feel the bike bogging out at 22 down to 19 again, I'll pull over and pop the cap to see if things improve for a time.

If they do, then I found (I hope) the problem.
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Regarding Flames.

That can't Possibly be a good thing!

That should be a Sure way to burn out the rear tire! I've had no Flamage, just the bog out when going all out on the open road for a time. I guess 20 minutes at 25+ MPH is a longer ride, so I'll pay attention to that as well. There have been times when we've been on a ride for an hour or so, but a 20 minute Full Out ride isn't really so common.

Usually around the neighborhood, we don't run into the bog out problem. Again, I'll pay more attention to how the bike acts from now on.

Hey guys, i got the chinese 2 stroke 80cc kit with about 250km on it so far. Im very impressed inthese engines but im having a bogging problem. When im driving for about 5 mins my bike begins to bog when i 3/4 or 4/4 of the way. Sometime just the slightest turn of the throttle with cause a bog. Can anyone help me? its getting plenty of fuel i think its something to do with the carb.

Having been messing with this concern for a while, here's what I recently did to maybe have the solution to the Bogging Problem. I re set the main jet in the carb. (The E Clip on the main needle has four grooves in it)

Factory Set is at level 2. I first lowered that to level 3, and then lowered it again to the lowest 4th groove.

What this groove setting does is raise up the main jet/needle when at WOT (Wide Open Throttle) for a Richer gas mix. < The lower you set the Clip, the Higher the needle opens up IN the carb at WOT.>

The Downside to having it set on the 4th groove is Idle Quality. I've had to turn in the idle mix screw damn near all the way to even keep it running at idle. So... I may soon compromise this by setting the needle clip back up to level 3.

By re setting this main jet/needle, I've seen a good top speed improvement go up from a steady 22 MPH up to a good and consistent 28 MPH, with no apparent bogging so far. So things are getting better a little by little.

Thanks for the reply, after i posted my message i took off my carb and took it apart and i also fixed the exhaust leak i had and my bike seems to be running much better, my idle is much better, i accelerate much better and most of all no more bogging. Im not sure what fixed it because i did not really repair anything i just opened the carb to take a look. Im interested in adjusting the jet you are taking about but im not sure what the jet is, is there a diagram you can direct me to? thanks for your time

I do not have a diagram or a pic available of the main Jet/Needle in the carb at this time. I can get one soon if nobody else has one to share here. In the meantime, I'll try to explain it the best I can via a text post here.

For starters, I have to admit that a Picture IS worth a thousand words, so please bear with me since I don't have a Pic yet. Really, it isn't as hard it may first seem to appear.

OK: Here we go. On the top of the carb is where the Throttle Cable connects to it. This came to me (and likely All of us who bought a China Kit) Pre Assembled. There is the 'minor' Cable Adjustment' in that location, and also the main 'Disconnect' as well. This Disconnect looks like a larger thumbscrew type of thing that can be removed from the top of the carb. This is actually what you're gonna want to do to re set the main jet/needle.

When you pull that off the top of the carb, you will then see that Two things happen when you twist the Throttle to WOT.

1) the plastic looking cylinder thing will allow more Air into the carb, and...
2) the little needle jet will allow more Gas into the carb from the Float Bowl.

You'll need to actually take apart this spring loaded assembly to find the E Clip on the little brass Needle/Jet. It can be a tricky move, but not too hard to do. Just Pay Attention to how it looks before you take it apart so that you reassemble it properly.

When you get this assembly Out of the carb, Note that it is installed in a One Way Only method. (Meaning, that cylindrical sleeve only works and fits One Way) There is a little 'ramp' on one side of the sleeve, and this belongs on the Left Hand side of the bike/carb. This Ramp serves the Idle screw on the left hand side of the carb, and that setting helps to get your idle at the proper/desired RPM. On the Right Side will be a slot so that you will be able to slip the spring loaded Throttle Cable out of this sleeve.

When you get that taken apart is when you will then see the grooves and the E clip on that Needle/Jet that I was talkin about. I called this as groove 1 - 4, 1 being at the top of the needle, 4 being at the bottom. As I said, mine was set as Stock at the second Groove. I have it currently set at the forth (lowest) groove, and what this does is allow More Gas through that carb at WOT. But remember too, that I now have Idle issues to an extent and may go back to the 3rd groove. (I'm still in the Trail Stages myself on this one.)

I hope this helps ya out some, and I understand that a Pic or two are worth a Lot more than my long winded Text Posts. I will do my best to get some pics together for you and anyone else who may need them.
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I CAN tell you this though. ...

Just Yesterday I did a Friendly Race with a fellow who claimed to have a 60 or 80 cc Engine kit on his bike with a Hundred Miles on it. I have a 48 or 50 cc kit with 200+ miles on mine.

I Won the race with my re jetted carb!!

Thank you very much for your detailed instructions, i just opened it up and ive realized i have more than 4 little slots, im going to try the 4th one because it is already on the 3rd one and hope for the best. Thanks again cowboy rider!!

I just got back from testing it out its know down to the 4th grove, there is 1 grove left but like you were saying before the idle really sucks, my idle screw is turned in almost all the way, but i must say the throttle response is amazing my bike just takes off now and hits an even higher speed, before i would top out at 50km/h know i get up to about 55km/h not to much more but the acceleration completely blows me away im tempted to put it to the 5th grove just to see how much better i can make it but my worry is my bike mite no longer idle. Thanks again for all your help