How can I increase the power on my MC-54-250b

[zfjelstad]

So I have an issue here after adjusting my valves to .004" intake and .006" exhaust (or so I think--that exhaust valve is hard to get to on this scooter), and cleaning out the carb and adjust the mixture to about 2 1/2 turns. The scooter doesn't stall during idling. The cdi, stator and rectifier are all newly changed. Fuel pump was taken apart and checked for cleanliness, and my fuel lines are clear. And finally I changed the spark plug.

After all that, I can only rev the engine up to about 5000 rpm and it doesn't go much past there. No popping or misfiring and no abnormal struggling sound. What can I do from here? Or am I just stuck with a weak scoot?

[barnie]

How much play do you have in your throttle hand grip on the handle bar. there should be very little play in the throttle b4 it starts to rev up. Your throttle may not be opening up wide open if there is a lot of play at the grip. That is easily adjustable. Let us know. About how fast are you running at 5000 rpm. Some tach's and speedometers are not real accurate. Barnie

[zfjelstad]

I don't think there is a problem with the handle bar throttle because I look at the throttle on the carb and I can see that it is swinging fully open as I rev the throttle hand grip. At 5k rpm's I think I am reaching max 30 to 35 mph. I checked all the vacuum lines and they are good and air tight. I even put gasket adhesive around all the vacuum receiver nipples tonight. Still no change. A couple things I am still questioning are the fuel filter as I do not know when it has last been changed, and the spark plug coil. I do take it back about the struggling noise. The rpm's slightly sway up and down at full throttle. Anything else you think I should be checking, I greatly appreciate your advice.

[prodigit]

35MPH sounds like a 50cc bike, not a 250cc!
Sounds like there's something seriously wrong with the bike!
On my 260, the limiter kicks in at around 7500-8000RPM.

Do know that on bigger bikes, the valve tolerance should be greater, not smaller than on a 50cc bike.

I know in my country on 50cc bikes they have a limiter on them, which you'd have to remove, in order to go upto ~45MPH.

If all parts of the bike are stock, try checking the air filter, and see if the passage ways are open and free (run the bike without air filter for a small test ride, to see if the limit is still there).

Also, most of the bikes have their peak at around 5200 RPMs. After that, they will lose power; the curve will go down, and it makes the same power below 5200rpm than above.
The only benefit you may have is the extra speed.

But the MC-54-250b (also called roketa) should have a gearing system. It looks to me that the cvt is working fine, but the gears are not working very well; or the gears are working, but the CVT is not.

[zfjelstad]

I definitely tried the air filter test and cleaned out all of my air lines. No issue there I don't think. One thing I should add is that it is very sluggish in getting to 5k RPMs. When I first got the scoot back in the spring, I bought it used and the guy who sold it to me said it definitely needed a tune-up. So cleaned out the carb and emptied all of the bad gas. I then mistakenly put in 87 octane right away after that and it pretty much sat the whole summer waiting to be fixed. Everything that I have done to it thus far (stator, valves, cdi, rectifier, another carb cleaning). I put sea foam in the gas tank and refilled with 92 octane.

I don't think I am too concerned about the gears yet considering it's not even reaching it's full potential in terms of RPMs, but I will definitely check them out. What condition should they be in?

[prodigit]

The bike should run fine with 87, but I'd recommend 89/90 (mid grade) on them. I find no benefit with using 93 octane fuel on my EFI bike. I doubt it will on yours.
87 fuel is only bad when pinging, which is only happening at max rpms or at max torque (like max acceleration).

[zfjelstad]

It was the fuel filter! Now she's getting up to 7K and 8K RPMs. I also changed out the fuel lines coming to and going away from the filter. I'm also going to changed the three vacuum lines as well including the plastic vacuum line junction (I'm upgrading to brass). However, the bike is still stalling after revving for a few seconds, and I just adjusted my valves last week. Anyone know where I should look to next to solve this problem?

[zfjelstad]

Changed the vacuum lines and messed with the fuel mixture screw on the carb. The scooter was back to doing the same old thing of dogging around 4K RPMs. Before, I think that I had a build up of gasoline in the carb after trying to start it after changing the fuel filter. I wasn't getting spark, so I had to change out the spark plug and it fired right up and was doing great until I let the throttle back down. Now, I can't get it past 4K RPMs. I then check to see the condition of the spark plug and it was dry. Can I get a confirmation from anyone that this is a fuel pump issue?

[scootinround68137]

pull your fuel lines and turn the engine over, you will know if its a bad fuel pump if you dont get any fuel out of the line.

[zfjelstad]

Thanks for the info. We're up and running now. I changed the vacuum lines and found that my carb mixture screw needed to only be open about a half turn. What's with that? I thought standard was about 2 - 2 1/2 turns.