G'day guys, I'll preface by saying I have little experience with carbys. So I am more than likely making a simple mistake, or missing something basic. I have a ZXR250, which I have refurbed the carbs on. I have looked through the manual and tried to set everything as per the stock settings. I initially had success only to notice the mixture was extremely rich. Upon further inspection I noticed that occasionally constant fuel flow would be coming through the carb into the intake (picture attached of exactly where from). Despite adjusting the float level to the spec of the manual, I decided to pull the carbs back out and check. They were on the lower side of the specification so I decided to add about 1-2mm to put the height at the upper end of recommended calibration. Initially no fuel was coming through and the bike ran. I later came back to it to find once fuel was connected the same issue occurred. I pulled the carbs again to check for any holes in the floats, but confirmed definitely no holes or liquid inside the floats (submerged each of them for extended periods of time to confirm). Also checked that when the floats are at closed position each of float needles are closing flow. Just wondering if anyone has any pointers or places to look, as I'm just about out of ideas. Not sure if it makes any difference but I am not using the fuel tank for fuel at this stage, just a reservoir going straight into the carb.
A common problem on Keihin carbs is the removable brass seat for the float needle. They have an o-ring underneath them, and when that starts to go brittle or even splits, the float needle and seat are no longer able to control fuel flow. You will have uncontrolled fuel flow past the seat, but only when the engine is running or the fuel tap is set to the prime (gravity feed) setting. The seat is retained in the carb body by a small screw to prevent them falling out. You have to remove the screw, then grab the outer edge of the seat with some grips or pliers, then twist and pull. Heat may be necessary to help loosen them, they can get seized/corroded into the body. You have to remove the float bowl and float to access them. This is what they look like:
Just to add to what @Linkin wrote... The O-ring he mentioned is indicated in the following image. Best place to get good O-rings and carb kits is Litetek: https://litetek.co/Carb_Kit_Kawasaki_ZXR250.html "Not sure if it makes any difference but I am not using the fuel tank for fuel at this stage, just a reservoir going straight into the carb." As Linkin said, your issue will only arise when the fuel petcock is set to "Prime". Running the bike from an external tank is the same as priming the carbs.
From my ZXR250C thread. You can see the o-rings have flattened out and have some corrosion starting, but have not split yet. Usually when you pull them off to replace them, the old ones are brittle and snap.
Float needle tips go hard , so I would replace them as well Float Valve And Needle Seat | Motorcycle Spares Warehouse
Thanks for your help guys, I had put new O-rings in when I went through the carbs. I think the issue most likely lies in the fact that my reservoir is essentially constantly priming the carbs. I'll put the tank back on and give it a go!
In that case, the float needles should stop fuel from flowing. If they aren't either the needle is worn out, the seat is damaged, or there is a piece of debris on the seat preventing a good seal. You can clean up the seats with a cotton tip and some metal polish. For the needles, as Grey pointed out the tips wear out and require replacement, if you haven't already. Last thing, sometimes the floats themselves get stuck and prevent the needle from seating properly.
Hey Guys, Just an update. So I've gone ahead and replaced float needles and seats. Confirmed that the float height is correct. Initially all good, seemed problem was solved, revving really nicely as it should. Plugged in all vacuum connectors put fuel tank and fairings back on and started momentarily, but smelt super rich, then eventually died and couldn't get it restarted. Pulled everything down and sure enough fuel all through the intake and clear signs that fuel had just been dumped. I've left it a few days since, as I've been super under the pump with work. Decided just to run it up quickly before work, with no vac lines, throttle cables connected and fuel tank on prime. Weirdly the bike ran fine for the 5 minutes I was testing... Even modulating the throttle by hand everything seemed fine all of a sudden. My vacuum system has alot blanked off and I'm starting to think my problem is pressure building somewhere in the carbs that is forcing air and fuel out after its ran for a bit. According to below I have 9, 12 and 6 running correctly. I've noticed that 8 and 7 are blocked off. My suspicion is that potentially with 6 venting to atmosphere my issue does not occur, and with it connected it is causing my problem with 8 and 7 being blocked. This is what I noticed in my test earlier today, but ran out of time before I could confirm. In my mind this hypothesis makes sense as 8 and 7 surely are responsible for the carb to vent out through the system after coming through 6?
You can entirely remove #10. And leave the carb vent hoses disconnected and venting to atmosphere. The valve is there as an emissions device. You should check which inlet manifold is connected the fuel tap with a vacuum line. If that was your port full of fuel, the. The diaphragm in the fuel tap has failed and fuel is going through the vacuum line into the manifold causing your flooding problem. If you have no problems when using a remote fuel reservoir then you know it's something with the tank/fuel tap side and not the carbs.
Seems like I've solved my issue. All the tubes going out of the valve were blanked, so I assume that having it connected was just forcing air pressure back through the carby (when I blew through that tube sure enough fuel came out just as it did with it connected) venting to atmosphere now, and working as expected. New problem now. I've got my idle screw 2 turns out and it's extremely rich though? Dying once warm with choke and a super delayed response when choke is off and warm. Hunting around for idle and eventually stalls a bit. Is it possible that since the vast majority of vac sources are blocked off I'll need to tinker to find a slightly different setting? New jets all the way through and float heights set at 13mm.
