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Blockage in Mikuni bowls

U

uteman

Forum Mentor
I am currently working on carbs (and other stuff) from 2 GS850 bikes each with Mikuni 32mm carbs.
The carburettor tutorial made available through GS resources has been much appreciated and valued.
However, I have 4 bowls that fail the "spray through test" described in the tutorial.
The attached photo should clearly describe the issue.
What I need to know is just what size orifice is in the depth of the deep hole I want to clear and how I can clear this.
Getting a brief run down on the function would also be appreciated.
Both bikes had sat for years and the bowls from the other carbs are quite clear.
Advance thanks to anyone who educates me further.
 

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Our mechanic has an Ultrasonic cleaner which can make any carby look like new.Try your local bike or lawnmower shop.
 
do you have access to compressed air? if so blow through the holes, from each end until the blockage clears. spray some carb cleaner down there first before you start and let it soak for a while.
 
I use the propane torch and heat the outside of the bowls and watch the gunk bubble out of the passages. Then I dunk the bowl in water to further shock the scale loose and repeat the heat one more time. Then I use a Qtip stick down the hole to scrub the hole a little and a wire to poke the bottom hole clean. rinse well with carb spray and compressed air.
 
The function: you will see that there is a small copper tube attached to the main carb body that slots into this orifice. This sucks up fuel from the float bowl for the choke / starter circuit.

The "Fuel to starter jet" on this diagram:

mikuni-carb-diagram-gif.3927
 
The well where the enrichener pickup tube fits has a check valve at the bottom. Fuel is pulled in through the hole in the bowl and goes through the one-way check valve to the brass pickup tube. Most of the suggestions in this thread won't work. If the check valve is clogged with gas-goo, you can heat, as Chuck suggested but then stick the straw from a can of carb cleaner in the bowl side first and spray till it comes out the top. Repeat but stick the straw in the well and it will come out the bowl. If the check valve isn't clear, the stuff is gas-goo but is crud that doesn't melt so well. You can get one of those cute jet clearing wire sets and use the most narrow diameter wire and work it in from the top (the well) and you can pop through the crud. Then flush with carb cleaner as already described. Heat can sometimes loosen even the dried crud type stuff but it won't boil oil like gas-goo.
 
Ive never known the wells to have any check valve. You can squirt carb spray from the top and it comes out in the bowl. If you shoot in the hole inside it comes out the hole in the top so where is that a check valved system?? What there are, however, are small holes at the top of the pick up tube which dump excess fuel thats being sucked up as your cranking the engine these holes should be looked at to be sure they are open also.
 
Agemax said:
do you have access to compressed air? if so blow through the holes, from each end until the blockage clears. spray some carb cleaner down there first before you start and let it soak for a while.
Click to expand...
Thanks agemax:
I have tried and re-tried that approach but do appreciate your response.
I see that I have been fortunate in receiving further responses so will work through those and no doubt get this problem licked.
 
chuck hahn said:
I use the propane torch and heat the outside of the bowls and watch the gunk bubble out of the passages. Then I dunk the bowl in water to further shock the scale loose and repeat the heat one more time. Then I use a Qtip stick down the hole to scrub the hole a little and a wire to poke the bottom hole clean. rinse well with carb spray and compressed air.
Click to expand...
This works for plugged jets too
 
geol said:
The well where the enrichener pickup tube fits has a check valve at the bottom.
Click to expand...
I have never seen a check valve. In fact, when they are CLEAN, you can shine a light in the inlet in the bowl and see it in the well in the edge of the bowl.

.
 
Steve said:
I have never seen a check valve. In fact, when they are CLEAN, you can shine a light in the inlet in the bowl and see it in the well in the edge of the bowl.

.
Click to expand...
No check valve in my BS carbs. I did have a plugged starter jet recently, the hole is VERY small. I filled the hole with spray carb cleaner and let it sit for a couple days, keeping it filled. It eventually cleared. Maybe a small sewing needle? The smallest wire I had was .020 and it was too big.
 
bobgroger said:
No check valve in my BS carbs. I did have a plugged starter jet recently, the hole is VERY small. I filled the hole with spray carb cleaner and let it sit for a couple days, keeping it filled. It eventually cleared. Maybe a small sewing needle? The smallest wire I had was .020 and it was too big.
Click to expand...
Thanks bobgrodger:
I am continuing to soak the bowls and appreciate your time taken in responding.
 
Thanks to geol:
Your time taken in responding is greatly appreciated. With all of the assistance offered I will get this sorted.
 
londonboards said:
The function: you will see that there is a small copper tube attached to the main carb body that slots into this orifice. This sucks up fuel from the float bowl for the choke / starter circuit.

The "Fuel to starter jet" on this diagram:


mikuni-carb-diagram-gif.3927
Click to expand...
londonboards: Firstly, I wish I could draw like that. Great effort indeed. Secondly, I cannot thank you enough.
 
Do the heat soak method to melt the gunk. Then shock it with a spray shot of carb cleaner. Poke it with the wire from the brush in the tutorial. Make sure you do it from both ends. Use the plastic tube from the carb cleaner and feed it from both sides. You'll know when it's clear when you have a good solid stream of spray coming out.
 
There is a check valve. I stand by this. It is often clogged be they BS or VM carbs. Go ahead and run a drill bit down through the well and you will find out a little bit about the check valve. If you try and use the bowl on a carb after that, you will find out why there is a check valve all over the floor of your garage.
 
geol said:
There is a check valve. I stand by this. It is often clogged be they BS or VM carbs. Go ahead and run a drill bit down through the well and you will find out a little bit about the check valve. If you try and use the bowl on a carb after that, you will find out why there is a check valve all over the floor of your garage.
Click to expand...

Stand by all your want, but there is no check valve. There is a restriction on the bottom but not a check valve. Why on earth would there be anything on the floor of the garage? Are you sure you're not thinking of the float valve?
 
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