#2 carb leak problem

work9to5

See you in the wind.
Bike cb550 75'
Mikuni carb , 2 gas inlets

Well every system on this current build/bike seems to be giving me problems. Currently and I hope lastly I've got a leak on #2 carb. Is leaking out of the drain hole (bottom stem of carb) and out the back of carb through the little inlet that connects to the main jet. Have checked the following things

-petcock is functioning normally
-fuel filter installed in fuel line, is functioning normal
-have set float at 22mm (stock), still leaks. Have tried setting float lower than other floats 22-25mm still leaks
-if I set it at 28mm it doesn't supply enough gas to run consistently.
- floats are old style, floated them in cup of water. They should be functioning correctly.
- needle plunger has as much rebound as others in the rack and they're new
-carb leaks when on kickstand or set up right on center stand
-carb does not leak when running but causes 1 n 2 plugs to run very rich
- fuel height in the bowl is well above where it should be. Pic attached of tube attached to drain to check level (when float is set at 22mm standard)
-have switched in a different needle plunger to see if it has affect with no effect.

The thing that's bother me is none of the other bowls are leaking. I set them all together to same height at first 22mm. Have only had a problem with #2. I realize I may just have to find the sweet spot between 25 and 28mm for it to run properly. But I'm having a hard time understanding what's causing this or run into this problem in the past?
07c274f97c173ebb0cfb478640fbc7a6.jpg
Anyone have any ideas? Or some where I should check that I havnt?

Pic is float set at 22mm


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Seems like the fuel is not being totally shut off on that carb, check to make sure the shut off needle and seat are clean and smooth. Any small bit of dirt or imperfection can still let gas flow into the carb.

Also, that fuel level is very high so make sure no gas flowed into the cylinder. If it did and gets into the oil it can destroy your engine in short order. Smell the oil to make sure no gas got in it.
 
Also check the following:

Take the carbs of,take the float assembly of,flip the floats and check the surface where the needle pin touches the float tang.had a few carbs where there was deep "hole"-like wear.This can cause the needle to stick sometime too.
take some really fine grit sand paper and sand the surface of the tang perfectly smooth (little piece of sandpaper will do the trick).

Then take a tiny piece of scotch brite (softest grit) wrap it around a drill bit that fits into the needle seat surface and carefully spin to "resurface" the needle area.Be careful not to scratch anything!

Reset the float bowl levels to stock.
 
If you pull the floats again, check them in gasoline or brake/carb cleaner. Water has a higher surface tension and may not show a leak.
 
So after posting I just sat there an drank a beer just staring at the bike. Decided to pull the offending bowl one last time before turning in. Removed the valve seat and found a tiny bit of rubber scrap under it. Changed the seat with another one I had and sealed her back up. When I was going back to attach gas lines, I noticed that one on the left that supplies #1/2 could've possible been at a better angle to supply fuel than the line that supplies #3/4. I've got a single spigot petcock with a T splitter in the line. I ended up cutting the line to 3/4 to get a better angle of flow. So possibly the line was dumping all the fuel to one side and the float couldn't keep up with the flow of gasoline?

Don't know which one solved the leak but its done with.

What do you guys use as a fuel line splitter? I've been using vacuum air splitter T lines with good results up until now. Is there a better (aluminum) option?

Thanks for the input


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Check for what I wrote.

I can leave my petcock open all night on my RD (split into two by aluminium piece) and it wont spill fuel.
 
I have seen constant leaks caused by a cracked/split brass overflow tube inside the float bowl. (At least on 750's) Check this...or swap it with #1 bowl and see if it follows.

Steve
 
Unfortunately I've ruled that out already. I checked bowl stew for leaks and fuel is rising above stem and even leaking out back of carb as I mentioned.


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Yeah I've tried that as well. I'm thinking now that I've got a clog some where on the gas inlets. From the portion of the carb under the needle valve. I think possibly one (or two) of the other bodies has a flow restriction and is causing more gas to be routed to #2. Going to go back in on my next day off to re-check that area next.

I do appreciate the advice tho, I find any suggestion when butted up against a problem with a bike either helps u find an area where u havnt investigated or helps brainstorming for other areas. Thanks


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Did you swap the needle and seat? Or just the needle. I do not see how a blockage anywhere would cause this problem.
Steve
 
Yes, I've swapped both needle and seat. With different ones from a different carb rack. Separately to check for impact of either. I'm thinking it could be a result from a clog in a different body because that's basically the only channel I havnt investigated. I've been looking at #2 this whole time without considering that all these channels are basically connected. I havnt removed bowls of other carbs to look for flow problems (all though I do know that all cylinders where firing. One other thing that points me in this direction is that 3/4 are plugs differently colored, leaning towards a good to possibly a little lean condition. While 1/2 are showing rich, which I was at first thinking leak/over-flow was causing. But I'm thinking possibly they are interrelated.

In your opinion a blockage would not influence more gas to be routed to another connected carb body? What's your reasoning?


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Even if more gas is sent...the needle valve closes and does not allow it into the bowl. If #2 is the only carb with a high gas float level....I think it is in that carb.
 
Ok, so I tore them apart late last night. And I'm hoping I have corrected the problem. I took down all bowls and cleaned each valve seat and area. I also shot a lot of WD throughout the gas inlets and then followed with quick bursts of carb cleaner. Some tiny particles did flush out.
4cdf0f5fdf1732e3a21093d9f5c5e389.jpg

I also flipped 2's valve and needle into 3's body. Just to see if the condition would duplicate. I set the bodies back up and boom no leak from 1/2. So I'm hoping problem is solved. I have to wait a day or two to test under running conditions tho.

I'm not exactly sure what changed could've just been my attention to detail with the seats and valves and float heights or could've been as a result of blowing the channels completely clean.



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