Carbie 250R playing up..

[brausi]

Hi All
Couple of months ago I replaced my stock exhaust for a yoshimura full system. Went to track days and done lots o running and the bike was fine. Suddenly, 2 weeks ago while doing Putty Loop, half way trhou the bike wouldnt rev more that 8000 and it start to strugle to go up hills or when i needed to get full throttle. Kawasaki change the needles from the carbie but the bike still playng up at 10000 revs and they are pointing the problem to the yoshi system.
Does anyone know about mechanic as im hopeless in this matter. Im booked to do my MOST test next week and i can't get the bike ready in time. as kawasaki is saying that i need a Dinojet to get the bike back to a 100%.
Any help or advice is appreciated..

[Strika]

Put it all back to standard for the test. If that fixes it, then it's definately a jetting issue. But it might be something else.

Partially blocked main jet
Kinked fuel line
Holed diaphragm
Coil/lead

[oldman]

I am not familiar with a Ninja 250. But you say you rejetted the carbs. If it has carbs then a dynojet power commander will not work as it is only for injection. If you are talking about a dynojet jet kit that is OK. I would look at the spark plugs as they will tell you how your mixture is; Black insulator=too rich, pure white or pitted insulator=too lean and tan just right. The problem could be several things but I do not think it is your pipe. Rejetting carbs is easy and the needle jet on the carbs I am familiar with is only used at low end, the main jet is the one you need to enlarge for higher RPM. Good luck.

[Strika]

I am not familiar with a Ninja 250. But you say you rejetted the carbs. If it has carbs then a dynojet power commander will not work as it is only for injection. If you are talking about a dynojet jet kit that is OK. I would look at the spark plugs as they will tell you how your mixture is; Black insulator=too rich, pure white or pitted insulator=too lean and tan just right. The problem could be several things but I do not think it is your pipe. Rejetting carbs is easy and the needle jet on the carbs I am familiar with is only used at low end, the main jet is the one you need to enlarge for higher RPM. Good luck.

Since the introduction of unleaded fuel here in Oz in 1987, the plug reading colours you have described no longer apply. For old leaded fuel, you are spot on, but with unleaded, the plugs run a lot blacker when the mixture is correct, than what they do with leaded fuel. Even for a very experienced mechanic it is next to impossible to read the plug of bike run on unleaded fuel. An Exhaust gas sensor would give a much more accurate assesment.

[brausi]

Thanks guys.
The spark plug was pretty black. Anyway, i've ordered dynojet direct from US as there was none in the country. Fingers cross i can sort the bike before EC..

[oldman]

The plug color is still relavent. Unleaded gas and the lean conditions that the factories tune their cars and bikes, (to pass emmissions) always makes the plugs run white but black insulators indicate a very rich condition and the high RPM issue you are having is no doubt due to fouled plugs. If you put new plugs in it would no doubt run good up to red line until the new plugs became fouled due to the excessive fuel. The adjustment that was made by the mechanic obviously was way too rich. As previously mentioned go back to stock and go from there. A too lean condition is bad also as it will burn exhaust valves. I would find a decent tuner as it appears your mechanic has not a clue to what is going on. JB and a brew will make all things clear.