RVF 400 problems with midgrade 5000 rpm

[javipop]

Hi, excuse me for my bad english , I am from Valencia , Spain, I would like to ask you a question about a problem I have with my motorbike, I bought a NC35 four months ago, the motorbike go very good until 5000 rpm , at 5000 rpm if I open the gas hard the motorbike don,t go up , I have to open the gas slowly and when the motorbike is in 6000 rpm it go very good again until 14000 rpm, the only problem is at 5000-6000 rpm in midgrade , I clean the carburettor and the main jets are 108 and the pilot jets 35 and the pilot screw are opening 1-5/8 turns out, I don,t see the needles and the float level, the exhaust is the original , do yo know anything about my problem? or is normally in this motorbike , Thank you very much

[MexicanGringo]

Hey Javi, the bike had this problem from when you bought it no? Those jet sizes you mention are the standard RVF jet sizes so they havent been changed.. The pilot screw is only for idle so dont worry about that.. Id suggest changing the air filter if its dirty, and the fuel filter while your at it, the problem is probably a lean condition at that rev range and placing a washer under the needle seat to raise it slightly may richen the mix enough to fix problem, or it will worsen but only way to know is to do it. The norm is a 0.5mm washer i think.. Check the ram-airs arent blocked and are making good contact with fuel tank bracket, they tend to come loose i think and then they do no ramming.. Do the filter changes first tho to rule them out as the problem. Also check plugs, if they too light in colour the bike is running lean, and too dark its running rich

[javipop]

Thank you for your answer, the air filter is new , and the spark plug are with a goog colour , I have to see the needle for see if they are the original , Do you know the refence of the needle original for a nc35? When I bught the motorbike was winter and it didn,t has the problem at 5000rpm as big as now in summer , here in Valencia we are at 32 degrees

[drjkill]

bueeenaaas...

[drjkill]

needle ref:16027-mr8-900

[MexicanGringo]

So your saying the bike only hesitates when warmed up and when ambient temperature is hot?

[javipop]

yes when I bought the motorbike in winter it run better than summer , other thing I don,t see is the Synchronization carburettor, Can it to concern the problem between 5000 an 6000 rpm?

[MexicanGringo]

Carbs are a pretty intricate sensitive system at higher revs, it could be that unbalanced cylinders create a problem but i doubt it would have happened in the short time youv had the bike.. Hesitation at whatever rev range means the mixture is quite badly off at that point, at 5k the mix is a combination of main jet and idle jet, the main jet being the adjustable part with needle heights& idle jet with pilot screw.. You can check the carbs are balanced yourself if you want, by hooking up clear plastic tubes with engine oil to the balancing points below the carbs, theres a screw for each cylinder, the oil is drawn up the tubes by the vacuum and then you compare each.. You should balance the carbs anyway even if its not the main cause..

Otherwise check the float heights and the float valve pins for free operation, on my carbs one of the pins was stuck in the valve body. To measure float heights you open the fuel reservoirs,they have three screws, with carbs on their side you measure from cover mating surface to bottom of float, should be 12.5mm.. before you measure make sure float linkage is just off the spring loaded valve pin

[javipop]

Thank you for your information when I have time I check all the things , ufff I have to do a lot of things , I am going to be very entertained

[MexicanGringo]

These checks are actually pretty quick to do, you can get prob solved in one afternoon cos i dont think this is too serious.. If you need photos let me know