Hi Guys, apologies if this has been asked before but it’s driving me nuts. I’m new to the CBR world and new to this forum. I was recently gifted a 1997 F3 that has been left sitting for about ten years. I cleaned the fuel tank and entire fuel system including the carbs. When started I can see fuel dripping out of the main jet into the throat whilst idling on some of the carbies. I purchased a cheap rebuild kit from eBay but didn’t solve the problem. I thought perhaps the kit was poor quality so I purchased an all ***** racing kit, polished all the float needle seats and tried again. It was worse, all carbs completely flooded with fuel running out the vent pipes. I removed the float needles and laid them out and found that the all ***** racing ones were slightly shorter than the originals. I have since refitted the cheap version and am back to fuel dripping out the main jet. I have measured the float height with vernier callipers and get 11.7mm and after researching your forum I believe that this is too high. Could the floats have been replaced at some stage by ones from a larger bike???? Cheers

 

So I took a chance and purchased a set of genuine Honda fuel float needle valves. During fitment they appeared to be worse by eye than the 3 non genuine sets that I have already tried, a lot less bounce on the springs. However I pressed on and fitted the carbies to the bike. Once started it seemed to run fine with no sign of flooding and crisp throttle response. I left running for 15 mins, switched it off and came back and restarted it several times over the next few hours, everything seemed okay. At this point I reassembled the bike and went for a ride. Rode well at low rpm but bogged down and fluttered once I reached 5000 rpm and couldn’t get it to rev much higher. I took it home and parked it up. 24 hrs later and the bike had hydraulic locked with cylinders full of fuel. I am losing faith in ever getting this bike sorted, I have several other fixer upper bikes on the go and am having no where near the problems like this one. I am still searching for advice if anyone has any ideas. Cheers guys.

 

Good job!!!

Always best to get genuine factory OEM parts. Even used, they're better than new aftermarket 3rd-party parts.

1. measure petrol-flow rate from petcock. If carbs are clogged, petcock usually is as well. Rebuild with new diaphragms, springs and seals.

2. If petcock is OK, then carbs need further disassembly and full restoration work, not just cleaning. BTW, spray "carb cleaners" no longer work due to removal of chlorinated compounds. Need to use scrub-brushes to clear out secret hidden passages inside carb-body. Ultrasonic soak. Micro soda-blast before re-assembly.

 

Thanks Dannoxyz, I really appreciate your thoughts. I do agree with you on the cleaning as I’ve never been completely confident that the carbs are as clean as they could be or even should be, especially considering the condition of inside the fuel tank when I picked the bike up. I am looking into ultrasonic cleaning now. Fuel petcock was replaced when the fuel tank was cleaned, albeit a non genuine non vacuum type I can only assume it is okay. However am I wrong in thinking that the only way the carbies could flood the cylinders whilst being parked up is if the fuel float needles were not sealing as they should? I have spent countless hours trying to make sure they are right, have polished the seats with cotton tips and brasso polish, and they do seem to operate freely on the bench and seal off from me being able to blow through the fuel supply line. This is my first time working on a multi carb motorcycle engine so any advice from people in the know is greatly appreciated. I’m that desperate to get this sorted that I’m even considering purchasing a second hand set of carbs off a low mileage wreck, but worried that I will end up with 2 sets of non functioning units. Cheers for any help.

 

Yes, only way to flood cylinders when off is leaky float valves. It actually takes 2 problems to cause this, bad petcock as well. Really should use vacuum petcock as 1st stage against flooding since no petrol will reach carbs.

I recall hearing something about new float valves being too loose and doesn’t sit on-axis to cover seats evenly all way around. Needs some kind of tweaking mechanism somehow… lemme see if I can find info.