[QUOTE=metricmotoguy;1353117]The stock jetting in the US is the same as you described. That flat spot is a sign of a fuel delivery issue or a problem with the air/fuel mixture at a given load. There are a lot of air and fuel passages in the carbs for this bike. Make sure they are all thoroughly clean. Also, be sure to synchronize (balance) the carburetors. While you are at it, check for vacuum leaks. Once the carbs are balanced, let the bike idle and remove and replace the vacuum line from each carb, one at a time. The engine should immediately start to run rough or stall with the vacuum line detached. That is a good thing. Replace it and try the next one. If there is no change when you remove the vacuum line, that means there is already a vacuum leak on that cylinder. Find the leak, correct it, and re-balance the carbs. If that does not solve the problem you can try raising the jet needles by adding a shim (or more than one shim) on each one. I am including a document on carburetor service that you may find useful.[/QUOTE solved my issue with a new fuel pump! Life is good, tha KS again,
Adie

 

I am circling back to this thread after a long break. I haven't had time to spend on this bike for a while. Now I am determined to solve this once and for all. To recap, this is a 2000 CBR600F4 with only 3K original miles. I got it with a K&N air filter, Two Bros slip-on, and a DynoJet jet kit installed. The fuel tank is clean. I changed the external fuel filter and petcock/internal fuel filter. The carburetors have been cleaned, adjusted, and synchronized several times. The bike was stumbling around 8K rpm and would not go past 110 mph in any gear at any rpm. I removed the DynoJet kit (including the air jet plugs), installed stock needles, and used a kit from carbjets.com (pilot jet #42, main outer jets #135, main inner jets #140, 2 shims per needle).

Bike starts and idles perfectly. Sync is dead accurate. No air/vacuum or gas leaks. Intake manifolds and air box are sealed tight. When I try to ride the bike, it takes off smooth and immediately bogs higher than 1/4 throttle. I have to let off the throttle and limp back to the garage or it will stall out. If I raise the rear wheel off the ground on a stand and go through the gears with the bike running and give it 1/2 throttle or more it does not bog at all. The trouble condition is only under load with a rider. My next two options are replacing the fuel pump and reverting back to stock jetting. As much as I want this fixed, I also want to know definitively what was wrong. So I won't be replacing the fuel pump and jets at the same time. I will do one then test ride. Then, if necessary take the next corrective step. I will update.

I welcome any constructive comments or suggestions.

 

Might be a long shot and left field but....

I bought a parallel imported F3 back in 98, at the time it was supposed to be UK spec but on riding the symptoms were similar, would not rev out and top end restricted.
I went back to the importer after having has a look at a UK bike and has noted smaller diameter exhaust, headlight dipping the wrong way and no on/off switch were the obvious ones. After these were replaced it also transpired that it needed a new ECU as it was clearly from a market that was 'restricted' power wise.

Not sure if this might have carried on with the F4... just a thought.

Other than that, I would revert to stock and go from there, put original air filter back in and see if you can pick up an original exhaust. You will then have a baseline. If it still has issues then investigate again but from known point

 

have you pulled the plugs to see how they are burning after experiencing this running issue? it almost sounds like a lean problem. if you suspect the fuel pump, you can troubleshoot the pump as described in the service manual. at least that way you can potentially eliminate it as a problem.

 

Bike ran perfectly fine when leaving showroom floor. It will run like that when restored back to factory-fresh OEM condition:

#40 pilot/slow jet
#132 1/4 main jet, #135 2/3 main jet
13.7mm float-level

For now, put factory air-filtre back and remove 2 shims per needle and see if it behaves better or worse. Then we'd have more data to go with for troubleshooting, such as it's running lean or rich. Currently you have no idea which it is.

BTW - all race bikes that have been dyno-tuned for increased power have gone down in main jet sizes compared to stock. No major manufacturer in their right minds would tune for max-power. Factory mixtures always too rich for safety. Just in case you get bad petrol on super hot day out in boonies. Or fuel-pump or filter or carbs starts clogging. Can blow up engine instantly if it's tuned for max-power under those conditions.