lance havana classic 125cc cuts out at 40mph
 

Scooter runs great until i get to 40mph. exactly at 40 it starts to cut out and I have to let off the throttle. Its suppose to go up to 59mph. Any ideas why it doesn't?

What year?
Fuel injection model?
Total miles?
Overall condition?
The Lance scooters are great quality products. Guessing kinda blind I would think.
Transmission damage of some sort?
Belt, rollers or clutch worn out?
If carb model, clogged main jet?
Unlikely, but a stator starting to die?
Wheels spin free when off the ground?

2014 carburated. 6000 miles and in great condition.
I checked the transmission a few days ago thinking it might have a spacer like the restricted 50s do. It didn't. Belt, variator and roller all seemed in very good condition.
But I did notice that the kickstarter was not moving at all (I've always just used the electric start).
Carb maybe? But at exactly 40 mph every time? I guess I could take it off and clean it. Probably a good thing to do anyway. I'll do it Thursday or Friday and report back. I'll check the wheels too.

I'm not sure were the carb is mounted on your Lance but if you can get the float off without removing the carb, you should be able to remove the jets as well. But even if you have to remove the carb, please note:

1) Be careful removing the float bowl. It will sometimes stick, you will get rough with it and catch the float getting the bowl off. If you bend the float you'll have to reset the float height. Its something I stink at.

2) Pull the jets and soak them in an ultrasonic cleaner like a jeweler uses. Don't go poking metal wire thru the jet holes as you can mess up the flow. Ultrasonic cleaners are the best way. Harbor Freight has them for around $100. I use a few drops of Dawn dish soap and distilled water.

3) Check the float height while the bowl is off. Its rare that they get out of factory adjustment but it can happen.

4) If you do the carb first and the problem persist, check the stator output. Again, very rare on a Lance. Plenty of You Tube videos on testing stator output.

Keep us posted. I'm thinking/hoping it's something simple.

5) Lastly, check the spark plug. Look at the electrode end for any contamination and make sure the plug boot fits on completely and tight.

I just thought of this because I had a car that did this nonsense. Vapor lock! My old Impala would be driving along and start loosing power. I'd let off the gas and it would drive normal again. Played this game for a bit and pulled over. When I removed the fuel cap I heard a whoosh noise. It got so bad in the end I had to use a channel lock wrench to remove the gas cap! I ended up having to drill a tiny hole in the cap until I would fix it correctly.

I took off the carb , took it apart, cleaned it but no difference.
I guess I am going to look for those videos on how to check the stator output.
I am also going to get a new spark plug wire because the one I am using right now is from a car (but the problem already existed before I had to use the car one).

Checked stator. All good. Got the right spark plug wire and boot.
....still having the same problem.
Any more suggestions?

It's hard to diagnose something virtually, and no one else is chipping in. If the carb jets were clean/clear, and you don't have vapor lock (rode it with the gas cap loose to see if the problem persist?). The stator checked out good and you checked the plug/cap. Checking the valves would be the next thing. Though they rarely go out of adjustment when one/both do strange things happen. After checking the valves and they are in spec, but the problem still persist, its back into the transmission. Transmission issues include:

Cracked/damaged roller(s).

Broken V-Slide in the variator.

Broken clutch spring(s).

Damaged torque driver pin guides.(My Zuma 50 had a damaged driver forever, it limited my top speed. To lazy to fix it as it only took 4 mph off my speed.)

Torque driver spring came unseated? Rare but it happens.

Belt out of spec. At only 6000 miles I don't think so.

Finally, this is all I can think of right now, but is the air filter clean and seated properly? I know Honda GET motors are very sensitive to the air filter being seated properly.

Keep us posted and good luck getting it right!

Check the intake manifold for a crack. Check all the vacuum lines for cracks. Start the scooter and see if you hear a hissing noise. If you do, find it.

Also, and this is out there, take off the exhaust pipe and see if it has a dent or something blocking it. Years ago I had a Bashan with a bad weld at the manifold that blocked off a third of the pipe. It wouldn't do 50 miles an hour before I replaced it. After that it would run all day at 55 mph.

Good call on the exhaust being blocked kz! I ran over a big rock (how is unimportant) and dented my down pipe under my Buddy 125. It killed my power so fast! I luckily found a used exhaust for a great price.

And intake leaks, Honda Helix was famous for intake leaks until Honda put a brace on the carb. Mine mainly backfired, virtually no power loss.

You can also start the scooter and spray all the hoses with starting fluid and see if the RPMs change. My old Toyota had a fun to find air leak under the intake/fuel rail. I NEVER would have found it without the starter fluid trick. Pain in the butt to fix as well!

I took the head of a while back. maybe the exhaust is not properly seated on the engine after putting it back on. Now that you mention it I can hear some hissing or ticking from where they meet. I will try to seat it properly over the weekend and get back to you. Thanks.

When running, hold a moist rag tightly against the exhaust tip. The scooter should stall in a few seconds. If it keeps running, you have a exhaust leak.