[joshtammi]

So, took my bike over to Hellessey today so he could take it for a spin and determine what was wrong with it.

He noticed it had a huge flatspot with anything under 7000rpm.

ran a wet paper towel over the headers, 1,2 and 3 all turned it to steam instantly, but no.4 didn't. so i'm thinking that the 4th cylinder only kicks in above a certain RPM range because over 8000 it goes great.

anyone had this problem and know what the fix is? i've replaced plugs, and i cleaned the carb out about a month ago. and now im just getting the shits:huh:

 

[juxt]

Is the 4th plug getting nice strong spark?
Have you tried switching the plugs to see if it is just the plug not burning hot enough?
It may be really simple..... here's hoping

 

[banana.logic]

try switching the pilot jet in no.4 to another carb and see if that cylinder then stops firing under 8000rpm.

 

[Blazzer]

what was the condition of the vacuum piston in #4?

 

[joshtammi]

vacuum piston was fine. im going to assume it is the pilot jet. i tested spark plug leads and no.4 was fine (even enough to give me a good shock when i had my hand on the frame accidentally)

fudge...i really hate having to pull apart that damn bike, i will have a look at the pilot jet tomorrow and get back to you? does anyone know where i can find some good pictures of a CBR250R carb? the pics in the manual i have are shiit and i cant follow them.

 

[banana.logic]

http://cbr250.com/forum/thread-231.html

check that out, some great pics there.