Any more speed?

[Wooogly]

My kymco 50cc does 40mph flat out, but when going downhill it feels like it could do more as it's still accelerating going up to 40 but then stops accelerating abruptly and then tries again. Is there any ways to boost the 40mph (yes mph, not kmh) limit?

It has a racing CDI fitted by the previous owner.

[johnson]

Doesn't really act like a racing CDI unless you get speed of light acceleration up to that 40mph.  And that's probably not your CDI doing that. 

[Bubba]

Well you could get a big bore kit and Im kinda big 6'7 210 Lb and with a 72cc Big bore kit on flat I will hit about 48Mph pretty quick. http://www.scrappydogscooters.com/139QMB_50cc_Performance.html

[naughty lee]

Start with the basics. Take your cvt side cover off and look at the variator. Odds are it will have either washers or a shouldered boss in it.
Follow the guide in my zx50 thread on boss skimming and variator inking. You'll get at least 50 mph out of it

[Bubba]

Start with the basics. Take your cvt side cover off and look at the variator. Odds are it will have either washers or a shouldered boss in it.
Follow the guide in my zx50 thread on boss skimming and variator inking. You'll get at least 50 mph out of it

I agree with you haha Mine hits about 55Mph the needle goes past 50 and im 212 pounds.

[naughty lee]

Racing CdI s and big bore kits are not always the answer.
Having the bikes fuel mixture set correctly and then gearing it correctly will give you the biggest speed gains.

[baddi]

Remove the restrictions in the air box and up jet to #84 or #86 and you should have the power you need.

The restriction is placed around 7 cm from the carb, cast inside the rubber connection.

Also, you can experiment with belt lengths and roller weights and you should be able to hit 50-55 mph indicated which of course is not the true speed. The highest speed i've been able to hit measured by gps is 72 km/h. Also, iridium spark plugs have a positive effect on the combustion.