Leaking mikuni carb

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LC Cnd
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Leaking mikuni carb

#1 Post by LC Cnd » Mon Feb 19, 2018 3:58 am

Fired up the LC friday and noted the right non choke carb (VM26) leaking (streaming) out the bottom over flow at the bottom of the petcock. Reset the floats to 21mm. Cleaned everything, reset the float height - still leaking. Changed the o ring on the float bowl to a new one again. Leaked. Took basso and slowly twisted the steel needle (new with a new float bowl) around until there was a grey mark on the needle tip. Tested the float - it floats. Tested it again - Leaked again. Put rubber tipped needle (RZ) and the carb leaked intermittently. Changed the float bowl and o ring again - still leaked and weak compression from the right exansion chamber. Some how, I suspect, the needle or the floats are snagging on something but can't see what. The float bowl is the proper one. What"s the issue cause I have run out of ideas. The choke carb is running perfect.

hondaror
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Re: Leaking mikuni carb

#2 Post by hondaror » Mon Feb 19, 2018 4:49 am

Did, at any time, you hit the carb float area with the handle of a screw driver? The shock sometimes, will cause the float needle to seat. Every once in a while, float assemblies will act up.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

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JonW
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Re: Leaking mikuni carb

#3 Post by JonW » Mon Feb 19, 2018 7:06 am

yep, always adopt the tap method. no need to hit hard, shock it dont dent it...
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MK
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Re: Leaking mikuni carb

#4 Post by MK » Mon Feb 19, 2018 2:47 pm

Reminds me of a mate I recommend that method in the early 90's.
The bloody jerk didn't remember which side of the screwdriver to tick against the float bowl and he thought the harder the better.
Ended with ordering a new one from the friendly local Yamaha dealership...
(To his defense I should mention he was a banker and not a mechanic)
Bye
Martin

hondaror
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Re: Leaking mikuni carb

#5 Post by hondaror » Tue Feb 20, 2018 2:02 am

Lol, Martin. That is why I said, with the handle of the screw driver.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

LC Cnd
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Re: Leaking mikuni carb

#6 Post by LC Cnd » Tue Feb 20, 2018 2:38 am

Huh. Reminds me when a soft drink can/bottle would get stuck by not dropping to the bottom of the cooler after payment - one quick smack on the side - voila. I'll give it a light tap out in the driveway after the Arctic out flow leaves the neighbourhood. Thx gents.

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Re: Leaking mikuni carb

#7 Post by whyzee79 » Tue Feb 20, 2018 4:27 am

Needle and seat? If the float floats and is set proper, then it has to be needle and seat problem I would think. You mention replacing the needle but not the seat. Just a thought.

hondaror
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Re: Leaking mikuni carb

#8 Post by hondaror » Tue Feb 20, 2018 8:41 am

If the tapping does nothing, you can use a chop stick to dress the float valve seat. You may have to whittle the chop stick down to size to get contact with the seat. Lap it like a valve. This action will hopefully soften any burrs that may be causing the valve seat to leak.
You should replace both parts on these old carbs, as a rule of thumb.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

oldracer
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Re: Leaking mikuni carb

#9 Post by oldracer » Tue Feb 20, 2018 10:20 pm

Check that the over flow pipe isn't cracked inside the float bowl. They've caused exasperation to many people by leaking gas when there's nothing wrong else where.
Dave.

LC Cnd
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Re: Leaking mikuni carb

#10 Post by LC Cnd » Wed Feb 21, 2018 12:45 am

Thx Dave. Ck'd it using water and it appear tight. However I am going to switch it with another. Did the ball bearing trick as I thought that would round out the opening at the bottom of the float bowl prior to lapping. The bowl is new; so is the needle. As noted in the photo the needle finish is not mirror-like. More lapping perhaps. But the tap might do the trick.
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LC Cnd
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Re: Leaking mikuni carb

#11 Post by LC Cnd » Mon Mar 19, 2018 3:24 am

Further investigation revealed none of the carb parts were the issue - it was minute debris (weld material?) from the bottom of the mini gas tank that flaked off jamming the needles open while carb syncing. The tank's un-removable fine mesh screen blocks any view below the screen where it appears the flakes oringinate. Everytime I tapped the carbs to settle the needles would dislodge the debris until the next time I opened the tank for more fuel. Hopefully a flushing of carb cleaner here will clean the tank.
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hondaror
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Re: Leaking mikuni carb

#12 Post by hondaror » Mon Mar 19, 2018 3:44 am

Great that you found that out. Glad you shared this info. Kind of crazy how fragile the system is.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

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JonW
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Re: Leaking mikuni carb

#13 Post by JonW » Mon Mar 19, 2018 9:26 am

well done for working it out!
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

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