fuel running through carb on idle

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Paul RF
Posts: 23
Joined: Mon Jan 12, 2015 7:45 am
My Bike: Yamaha R1

fuel running through carb on idle

Post by Paul RF »

This has been an ongoing issue over the last 4 weeks.
Bike was dyno'd Dec, running ok, carbs drained, removed left over winter, refitted.....nightmare started.
Initially wouldn't start, when it did, wouldn't tick over, so stripped and cleaned carbs.
After a lot of messing about, went back to standard needles, N77s, 35 pilots and 100 mains. Got ram air, for racing only. Set float height at 11 and 12.
Found a one point 2, 3 and 4 had fuel running in on tickover, replaced float needle seat O rings from cradley.
I found these went in easy, but am certain they shouldn't be that easy. Still leaking.

Had a spare set of carbs, 32mm on the shelf, stripped and cleaned, used the body's and then fitted parts from mine, except brass seats which are 2.4 on these, fitted another set of new O rings. Improved as now only number 4 has fuel running in on idle, only starts after a short while.
Ive replaced this O ring multiple times, replaced the brass seat, checked how smothly the float needle moves inside it, but still can't stop the fuel running in.

Ive measured everything I can think of, the brass, the irifice it pushes into, checked for damage, cleaned, etc, but still there.

Is there anything else it could be, because I can't believ I can struggle this much with one O ring?
Any ideas appreciated

If you think iv'e missed anything, just ask, let me know
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banner001
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Posts: 2585
Joined: Sat Sep 24, 2011 3:27 pm
My Bike: ZXR400 L4
Location: Nuneaton

Re: fuel running through carb on idle

Post by banner001 »

Swap the float and the needle from carb #4 to #1 and see if the problem moves
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
Paul RF
Posts: 23
Joined: Mon Jan 12, 2015 7:45 am
My Bike: Yamaha R1

Re: fuel running through carb on idle

Post by Paul RF »

Ok, so I tried swapping the float and needle with #3, just coz it's next to it and working, problem didn't move. I'd refitted brass seat and seal, initially thought it was ok while ticking over, blipped the throttle and fuel running down the carb.

Removed carbs, RAM air and checked inlet rubbers, clutching at straws here but O ring replaced fairly recently and in good cond, applied some sealant for the hell of it.

Tried numerous other attempts, one thing I did notice, if I lift the slide slightly it stops, why would that be?
Let it drop back down and fuel running through.

I'm running out of ideas, patience and time to get this sorted and it's proper giving me the hump now

What else could cause this?
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banner001
Track day God
Track day God
Posts: 2585
Joined: Sat Sep 24, 2011 3:27 pm
My Bike: ZXR400 L4
Location: Nuneaton

Re: fuel running through carb on idle

Post by banner001 »

so its leaking fuel through the carb, not via the overflows?

and if its leaking through the carb, i take it that its leaking through the "main jet" opening, i.e. where the slide needle slots into?
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003
Paul RF
Posts: 23
Joined: Mon Jan 12, 2015 7:45 am
My Bike: Yamaha R1

Re: fuel running through carb on idle

Post by Paul RF »

yes exactly, it's not overflowing but leaking through the main needle orifice if that's what you want to call it.
When I pulled the slide up slightly it stopped, that I wasn't expecting
RebuilderGuy
Posts: 11
Joined: Mon Jan 27, 2020 9:02 am
My Bike: ZXR 400R

Re: fuel running through carb on idle

Post by RebuilderGuy »

seems like a o-ring failing or a damaged jet?
try changing the parts from the other ones with the leaking one.
japmannslim
Posts: 25
Joined: Mon Dec 26, 2011 6:22 pm
My Bike: zxr400l9
Location: Birmingham

Re: fuel running through carb on idle

Post by japmannslim »

Hi I had this trouble after purchasing the rubber “O” rings from Cradley. I got my carbs on a bench and fed fuel to them via a portable fuel tank. Noticed fuel coming out of one of the carbs, fortunately I had a number of none Kawasaki “O” rings to replace the OE ones. Problem solved. Contacted Cradley Kawasaki who could not understand why I had the problem. Gave me a full refund.
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