Cbr400rr 1988 nc23 fuel overflow

[Lloydy]

Hi. This topic may have been done to death but I have searced other posts/threads but I havent found an answer.
I have stripped and cleaned the carbies and reassembled.
I tested float needle valves and they seemed to work. Blowing into fuel line and moving float. Bike runs well but I have not synchronized them yet.
After starting the fuel eventuslly flows out the breather hoses. I have disconnected the fuel pump snd the bike still runs and revs but I havd not ridden it.
I understand that......
1. Newer models were made without a fuel pump.
2. My old cbr250rr had no fuel pump and ran on gravity with no ussues.
3.. A motorcycle mechanic I bought some carby parts off locally ( who has rebuilt 2 of these) said the fuel pump is not required.
4. The fuel stops overflowing with the fuel pump off and bike runs and revs.

My questions I guess are.
Does the fuel system have some kind of regulator?
If so..... it must be in the pump?
Even if the carby floats work... could excessive fuel pressure cause this?
When I reassembled the floats and valves....the valves could sit either way on thr float. Would this make s difference?
Even if the fuel pump is unnecessary... I would prefer to fix the problem.

Any other thoughts.


I kind of know what I am doing... i have stripped cbr carbies before and balanced with no issues.
I have also stripped 650 engines to crank case and rebuilt.

[Gimly56]

Have you tried replacing the fuel pump relay?....

[Lloydy]

No I havent. What would tell the relay to acivate the fuel pump? Or what would tell the relay to turn the fuel pump off? The fuel pump does not seem to run unless the bike is running. In my car the fuel pump primes on turning the ignition on. And stoppd when pressurised.

[eeriedess]

No I havent. What would tell the relay to acivate the fuel pump? Or what would tell the relay to turn the fuel pump off? The fuel pump does not seem to run unless the bike is running. In my car the fuel pump primes on turning the ignition on. And stoppd when pressurised.

hi lloydy--had a prob similar last year on my cbr400rr and the prob was the SPRINGS in the float needles--take out all the float needles and soak overnight in petrol---dry off and GENTLY press the float hanger pin up and down to make sure they are all free and not catching--also due to fuel leaks on mine i dismantled the carb set and replaced all the seals with VITON SEALS(ethylene in modern fuel will kill the old rubber seals in these carbs and they will leak from the metal supply tubes /float bowls/ drain screws/--u get the idea ---carbs now perfect ---seals from thailand (LITETEK.COM)AROUND £30 ALL IN AND THEY DUE A HUGE RANGE FOR OLDER BIKES.hope this helps. Col

[Lloydy]

hi lloydy--had a prob similar last year on my cbr400rr and the prob was the SPRINGS in the float needles--take out all the float needles and soak overnight in petrol---dry off and GENTLY press the float hanger pin up and down to make sure they are all free and not catching--also due to fuel leaks on mine i dismantled the carb set and replaced all the seals with VITON SEALS(ethylene in modern fuel will kill the old rubber seals in these carbs and they will leak from the metal supply tubes /float bowls/ drain screws/--u get the idea ---carbs now perfect ---seals from thailand (LITETEK.COM)AROUND £30 ALL IN AND THEY DUE A HUGE RANGE FOR OLDER BIKES.hope this helps. Col[/quote]
Hi.
I stripped them all and soaked and cleaned with throttle body cleaner too. They were all free and moving. I dont remember any springs. Just gravity (fuel low) and closed (fuel full). They seemed to be functioning. The float bowl seals were a bit flat so i did use some non hardening 3 bond fuel gasket sealer. Perhaps that has messed with them but I dont think so.
I have never ridden the bike so I was hoping to test that gearbox was all ok etc before spending lots of cash.
I guess i can strip again and test. Order some gaskets.
I tried ordering full carby kits fron nsk or something like that in the uk but after multiple emails and no reply......

[eeriedess]

HEY LLOYDY
yes the springs are an integral part of the float needle---one end is a fibre "point"which is what seals the carb fuel inlet to the floatbowl when the fuel level is correct , the float rises, pushing up on the float needle and stopping the fuel flow from continuing--so if the float needles do not push up and seal the inlet the fuel continues to flow and discharges out of the overflow pipes.
Take off a float bowlcover---remove the float pivot pin and the float will be detached but do not lose the float needle because it has nothing to stop it falling out of the carb body--and as i mentioned before if you hold the body of the needle between your fingers and push gently on the "pin" end you will find it has a weak internal spring---the spring is there as a "shockabsorber"so that it soaks up movements of the petrol in the bowl when riding on bumpy surfaces---if it was not there every time you went down a manhole cover or over a speed hump it would stop the flow of fuel which is highly undesirable
Hope this helps.
col

[Gimly56]

The carbs are ALL overflowing though....I'd say it is something really simple???

Can you take the tank off and post a photo of the fuel pump and carbs???

[Lloydy]

I will take some pics.
I have eliminated the fuel pump as am issue.
Pulled apart. Checked function. It has a internal pressure cut off.
A short video here. The pauses are when i put my finger over the output hose.
https://youtu.be/ycT9BM5rsyc

[Lloydy]

The carbs are ALL overflowing though....I'd say it is something really simple???

Can you take the tank off and post a photo of the fuel pump and carbs???

Pictures here.
https://plus.google.com/107184893076653 ... JDhdwcPsT7

[Gimly56]

Yikes. That's a very liberal amount of gasket glue??!!

Errr I'd buy some new Carb gaskets for starters. Get rid of ALL of that gaset sealer/glue too. If any of that gets into the jets and internals it won't be good. You shouldn't need that much sealer. If using new gaskets you wont actually need any.