Topping out at 20 mph...Too much fuel ?

[Airbuzz]

Hi everybody. For the past couple of weeks my 47cc has been bogging down at 20mph. It will accelerate well to 19mph and then at 20mph it bogs down, dropping to about 18. This occurs whether you give it full throttle or partial throttle (just enough twist to accelerate to 20) so as to not flood it out.

The engine used to run fine. One of its sweet spots was at about 25-26mph. Then all of a sudden it started bogging at 20.

You may ask, has anything changed? I had to replace the float a few weeks ago. The original leaked. But I swear the bike ran fine for a while after it was replaced.

My saga continues and here is where it gets interesting. I was getting accustomed to the 20 mph top speed, so I just figured that I’d allow my 10yr old son to ride this while I build a new one for myself. 20mph is fast enough for him.

Well yesterday he coasted into our garage on his ride and said he figured out the problem, stating that he was again able to hit the 25mph sweet spot. His method was to starve it of fuel by mostly closing-off the fuel shut-off valve on the fuel line.

The whole time I thought that it was not getting enough fuel. Now it appears that it was getting too much. Any Ideas of what I can do to fix it so I won’t have to use the fuel shut-off valve method?

[TexasDav]

The two things I would check, and are common, Is an air leak(spray carb cleaner around the intake and see if rpm changes) and be sure your motor mounts have not loosen any(causing your fuel to foam at high rpm) Good luck

[Easy Rider]

You might want to clean out your carb. Remove the needle and blow it out with carb cleaner (maybe it's not closing) and also check your jet. I had the same problem and I found out the jet was semi clogged.
Or it could be a common dreaded air leak.

[Airbuzz]

But Why Would Starving It Of Fuel By Nearly Closing Off The Fuel Pet-cock Valve Make The Engine Run Fine ?

[Easy Rider]

I think because you need to close the petcock, its getting too much fuel. That's why I think your needle is not closing and its getting too much fuel. I recommend checking your carb again to make sure its closing. What you can do is take the bowl off and push the float up. If fuel keeps coming out, the needle isn't seating.

[TexasDav]

Well if it was foaming of the gas then keeping the bowl empty would have no gas to foam, but that is just a guess. I just know mine lost power at was once there and I fixed the air leak then when my motor mount got just bearly loose I lost power again, thighten it and fixed the problem and my logic was all wrong with my thoughts of the carb being the problem. If your jets are the same and your float is working back the way it was before you replaced it, then it must be somewhere else then the carb it's self, I would think. These little motors are tricky even if they are simple. Best of luck and let us know the fix.

[Airbuzz]

I'll perform all of your suggestions tonight and report back.

I'm intrigued most by how the fuel level in the bowl would cause my top speed bogging. I can't understand why this would have an effect (admittedly I don't know very much about carbs) but I did notice some fuel showing up on top of the engine possibly spilling out thru the airfilter housing. Maybe at full throttle when the bowl fuel level is lowered to a certain point, the release of fuel from the float fuel metering pin goes from a little stream to a flood, then the bowl is over full, and it spills out the air filter housing, the fuel filter being saturated increases the fuel-air mixture and also restricts airflow...hence the bogging. Huh...maybe this is it. I'll check it out.

[Finfan]

You might also check your air filter. I had a similar experience once when I forgot to close the choke and the engine wasn't getting enough air.

[jasonh]

Once the motor is warmed up, turn the choke fully on. If the motor doesn't die, you probably have an air leak.

Just thought I'd throw my $0.02 as a side note...these are not for kids. A kid that's good at riding a dirt bike, maybe, but not for most. Especially where there are cars. Most states won't let kids ride these anyway.

[Bikeguy Joe]

Alrighty then....you say it's too rich.

Clean your air filter, check the float level, and also make sure the float is not sinking- like if the new one cracked or developed a hole.

I would also change the plug, not clean it, change it.