Is this a compression problem or a fuelling 1?

Question

I have bought a cagiva mito 125 for the track and after driving at pretty much its limits for 2 months (pretty much always in the 9000+rpm as this is the power band) the bike now coughs and splutters from 6000 up and refuses to above that now. it feels like either fuel starvation or compression to me but i just ride bikes and dont know much about the engineering side. could be blocked jets in the carbs or a blocked gauze in the fuel line inside the tank. have no idea so any suggestions would be great. hope its not a compression problem.thanks in advance

Answer 1

low compression = hard starting

rich mixture        = black soot on plugs

desert camel has it right if it has a power valve that's where i would start

if you have not changed anything (air filter ,2 stroke oil type /mix)

the mixture should not change enough to cause problems

loss of power on this type of bike is normally mechanical failure

if you track the bike you should set up a service schedule you do after every event, lubricating cleaning and checking things like brakes,pivots cables, carbs etc that way you will learn loads about your bike without it being broken.  

Answer 2

check the powervalve servo motor is still working,also give it a new plug..and blow out the float bowl and jets...

Answer 3

get a compresion gauge!

Answer 4

If it's what I'd call "spluttering", then it sounds like an overly rich mixture.  Both too rich and too lean mixes will make an engine miss, but too lean tends to be a sharp, sudden miss while too rich tends to be a softer, more slobbery miss.  I know that's pretty vague, but if you could compare the two, it would be readily evident.

I seriously doubt it's low compression.  That usually just results in a loss of power and with 4 stroke engines, lots of fumes vented from the crankcase and high oil use.  Low compression usually sneaks up on you gradually and even with a busted ring, an engine will still run fine but with loads of oil smoke or fumes.

Were it me, I'd first check the air filter to see if it's dirty.  Also, don't overlook the ignition.  A lot of "carburation" problems have been fixed by working on the ignition.  Put in a new spark plug and see if that makes any difference.  Be aware than a spark plug can look perfect but will misfire, especially with low powered ignition systems.      

Answer 5

Probably a mixture of everything you've mentioned. Constant high-revving will burn and wear the  piston rings. The head probably needs a good clean as will the in/outlets. Fuel pump and inline filters will need a clean and flush too.

Strip it down slowly, take decent photos as you go and you'll learn what you need to know.