My fuel/related problem.

[KevTM]

so i have this problem with my bike, if i ride it fast it's generally ok but if i'm cruising or around town it'll eventually run and sound like it's running on 3 cylinders or whether it's just a lack of fuel i dunno, i think maybe it is. After it does this if i slow down to a stop/idle it'll conk out and it wont start unless i turn the fuel tap to "off" then hold the throttle wide open until the revs will eventually rise from idle (or if i leave it for a while it'll start again).

The bikes a zxr750 l3. i don't think it's the tank breather, well there's no pressure from the cap when i open it when it starts to conk out.

I had problems with water getting into my tank and carbs. I've taken the carbs off completely drained them, drained the fuel pump and all lines and the tank obviously... put it all back together and it done it again within ten minutes.

I'm wondering about the breather on the tank, it only has one? i assume this is a breather and an overflow, thing is it was blocked but i blew through it and it cleared but now even with very little petrol in it petrol escapes consantantly.. i have no idea how these breathers in the tank work, is there a valve or something inside? i heard you have to cut the bottom of the tank to fix this prob, or get a new tank?

any ideas ? it's killing me.

[gsxrpeak]

have you checked the spark on the bad cylinder when your having the problem? thats the first thing i would check.

i would also take of the carb and spend a long time going through them
take out all the jets. push a wire from your wire brush through the jets and clear them with carb cleaning.

if that dosnt help. get it running on 3. take out the spark plug and put some petrol down the cylinder. then start it to see if it runs normal for a second or 2? if it dose you know you still have a fule problem

if that still dosent work i would do a compresion test . it may have low compression on one cylinder due to a valve.

kris
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[finpos]

Few things to clarify:

I assume this "breather" is a tube coming out of the bottom of the tank, seperate from the fuel tap. Are you sure it's not the (water) drain for the recess around the filler cap? If it is, the fact that petrol comes out of it and that water gets into your tank is not too good a sign, and would neatly explain the advice that you're going to have to cut the tank open. There will be a tube internal to the tank which connects the drain in the recess to the tube on the bottom, and you could suspect this is borked.

The symptoms you describe about the bike conking out could be due to more water getting into the tank, which is consistent with the above.

The breather for the fuel tank is normally built into the fuel cap itself.

finpos.

[Ichy]

I really can't remember what a breather system looks like on a bike its been so long since I saw one, but anyway.

Maybe you could block the breather and go for a ride with the petrol cap open to see if it is the breather causing problems?

I know cars will have a one way valve fitted to the breather, I wonder if your bike is the same and when you blew through it to unblock it; it stuck open? Still find it unusual for fuel to come out when the fuel level is low, I would of thought that the breather would feed from close to the top of the tank, maybe the pipes rusted through inside the tank?

Have you tried turning the tap to prime so its not relying on vacuum for fuel supply? Any difference?

[Kickstart]

Hi

If it is fuel related, then to me it sounds like excessive fuel. Personal guess in that case would be one of the floats is sticking. At high speed the bike is using enough fuel to cope, but at low revs it is dumping a load of excess fuel into one cylinder.

A blocked breather would be worse at high revs.

All the best

Keith
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[KevTM]

well i'll take the carbs off again and go over them, tried a lot of carb cleaner etc on them.. but i never tried to clear the jets with anything solid- so i'll do that..

i think the pipe in the tank must be rusted then because it was blocked (rust?) and now it's leaking petrol (which it shouldn't).. so waters still gonna get in the tank.. i just never knew how that water drain system worked, a pipe or whatever..

ok cheers.

EDIT:

thanks kickstart for that advice, i'll strip the carbs down and check that too.

[Kickstart]

[KevTM]

right well i stripped teh carbs... only obvious thing i noticed was the needles on the slides, two of them are sort of pitted near the tip, would this cause the prob?

[bish777]

probably not.

The problem you describe sounds like a stuck or incorect float height or a knackered float valve.

If you take the float valve out there is normally an o-ring around it. If this perishes it will cause what you descriibe as it will allow far too much fuel past.
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