Loss of Top Speed



New Member
Jun 30, 2008
I have a Dax Titan XC50 kit. I have logged about 300 miles and am approaching the end of the break-in period. Though things seem smooth, I feel that my top speed is now around 25 mph or less. I was at around 30 mph. What can be done to bring the speed back up? I have noticed of late also that there is no difference in speed or RPM as I continue to turn the throttle from about 80% full throttle to 100% throttle. I have verified that I have full range at my carburator.

Jemma Hawtrey

New Member
Dec 29, 2007
Essex, UK

Check valve gaps
Check spark plug condition - you want a nice light tan brown colour - anything else and you have a problem. Pale/white running lean (very bad) black and oily - oil blow by (not good) black and sorta sooty (engine too rich)
Check exhaust - while running it should be impossible to see anything unless the weather is very cold - black smoke at high/full power (too rich), blue smoke at anything over tickover (oil blow-by and combustion... bad.)
Check fuel supply for crud and or disassemble carb (DONT if you dont know how to or havent done it before, bits will go ping)

Check -

Brakes for binding - that will noticably affect top speed although it sounds engine related tbh
Check fixings and fittings

Do you have a speedometer fitted - if so do tests to see if you're down on speed or its just the engine bedding in makes you think so

Have you changed fuel suppliers or gotten it from a different garage - that can have an effect.

Check all intakes/outtakes are clear and operating normally - increase in back pressure.. not great and will stifle the engine...

Good luck

Jemma xx


Custom MB Buiilder
May 7, 2008
Houston, Texas
A bad or weak ground wire will cause that. Over time it will also kill your CDI.
At high rpm that motor needs all the fire it can get. Also check your air cleaner, it can do the same thing,but won't affect the CDI.