NSR 250 timing
Starts, and both cylinders run at same speed, however open the choke and one cylinder only fires half of the time (judged by one exhaust expelling smoke twice as often if not more) above around 4000 rpm both cylinders seem to be firing at same rate again. riden heaps with this condition and hasn't worn out yet but still worrying if no gas/oil making into one cylinder during idol maybe it will seize. tested ignition and cleaned carb any ideas on what else it could be?
Motorcycles - Honda
Answers & Comments
Just a hunch. Clearly there is a fuel issue on one of the cylinders. Although you cleaned the carb, please confirm that the intake valve is clean and/or reed valves are working properly. It is possible that the 2nd cylinder is only firing occasionally even at the higher RPM but it's less noticeable because of the engine's inertia at that speed makes it "seem" to be running smoother. The clue lies in the fact that the engine runs smoothly at idle when the choke is applied and starts to miss when choke is open ... this is indicative of fuel starvation. And yes, on a 2 cycle, a lack of fuel means a lack of lubrication.
Out of curiosity, take both spark plugs out and crank the engine. Do this outside away from an open flame. Compare the amount of misted fuel that comes out of each cylinder head with the choke closed and then again with the choke open. If it isn't even then the cylinder that is blowing less fuel is being starved. This should identify the problem cylinder and help to narrow down the elements left to troubleshoot and replace/repair/clean. Good luck and hope this helps