Mikuni float bowl passages

[chuck hahn]

You dont fit a Qtip into the small hole at the bottom and I never said so Agemax!!! You clean the big main hole with the Qtip..STICK part ( not the cotton end on because it wont fit ). And you use a thin wire to poke the tiny hole at the bottom. I have a wooden handle wire brushn that then wires are plucked from for poking holes and the jets. They are real tiny and perfectly straight..great poking wires.

And yes, it is my OPINION that its hack advice. If the hole is that plugged just how would you remove the bowl..seems it would be sealed around the pick up tube also..right?? If the bowl is off then the layer is minimal and the dip will VERY VERY EASILY dissolve it.

[OldVet66]

I agree about the proper use of jet drills, but his description of setting the depth and "thunking" indicates using a power tool. I had been warned their use was strictly by hand and to be careful at that.

[tkent02]

Totally agree. i have a set of micro drill bits, 0.3mm up to 1.6mm and quite often use them in a small precision hand held "chuck" to clean crud from jets and tiny orifices! Done carefully it clears them quickly with no harm,

A pin vise is what it's called here. Useful tool. Don't need them on carbs much but I suppose if it was blocked up hard enough….. But if the easy to reach choke feed hole is that bad, just think what the other passages where a drill bit won't reach are like. It's going to need to soak in the dip or be ultrasounded for quite a while.

The OP never mentioned turning the bit by hand, he sounded like he was using the power tool.

[mikestp]

A pin vise is what it's called here. Useful tool. Don't need them on carbs much but I suppose if it was blocked up hard enough….. But if the easy to reach choke feed hole is that bad, just think what the other passages where a drill bit won't reach are like. It's going to need to soak in the dip or be ultrasounded for quite a while.

The OP never mentioned turning the bit by hand, he sounded like he was using the power tool.

I have used a small power drill to clear the more petrified crap out. The passage is not a jet. It is not acting as a meter. It is simply a hole drilled to allow gasoline from the bottom of the float bowl to get to the brass pickup. That brass pickup IS metered. I suggest cleaning it but the holes in any of the brass parts of a carb might be metering holes and to drill those out would likely damage the jet.... unless you use small bore "jet drills".

For the passage in question a 1/64th size twist drill is smaller that the diameter of the passage at the bottom where it meets a cross drilled passage at a 45 degree angle. I also recommend using the same twist drill from the bottom to ensure it meets the vertical passage.

I most often use a twist drill with my fingers to bore out the crud. But when I have really hard crystallized concrete in that passage, a power attachment at low speed works when even poking, prodding, and cursing wont work. Make sure the drill is in the chuck to the right depth so as to not drill through the float bowl (although if that is what you do, then I think fixing bikes is not for you.) Some of these float bowls out there are soooo badly crudded up soaking in Berrymans for a week did nothing.

I have a lovely ultrasonic tank (2 gallons) that I bought from a US Government lab for 50 bucks... Even it does not get that tight passage cleared. I have used gun wash as a carb cleaner, with generally good result, but it wont ungunk that crud. I have always looked for shards of metal in the debris that is drilled out and I have never seen any. Be careful, drill slowly, measure the length from your chuck tip if you use a power attachment, and go slow.

In general THINK before you do any task such as this. I would have thought that did not need stating, but I will refrain from giving advise if this is what the results are. Silly people squabbling over their own misunderstanding.

I will continue to repair Mikuni carb float bowls in this manner. In my opinion it is the only method that gives me great results. I see so many bikes that stall on a quick twist of the throttle and this passage is the likely culprit.

All the bikes I have done have miraculously lost the temperamental part throttle response, and run as new again. I assume of course that the rest of the carb is not cross threaded, the jets are clear, the carb passages are clear, and clean. The floats levels are set and the needle and seat are sealing.

If you fail to clear the passage so that it flows (not just seeping when you spray carb cleaner down the vertical passage.) Try the drill. you will be pleased with the results.

Mike...

[chuck hahn]

Same with all the ones I do WITHOUT a drill...apples and oranges. And the only thing that "meters" it is the tiny hole in the end of the brass tube. There are 4 bigger holes at the top right where the tube goes into the carb body..those dump the excess fuel back into the bowls. And they allow a little air to be mixed as they are sipping fuel initially.

[mikestp]

Same with all the ones I do WITHOUT a drill...apples and oranges. And the only thing that "meters" it is the tiny hole in the end of the brass tube. There are 4 bigger holes at the top right where the tube goes into the carb body..those dump the excess fuel back into the bowls. And they allow a little air to be mixed as they are sipping fuel initially.

I just don't have the time to hand clean all the parts of the carbs I do. I soak em overnight and drill the next day, soda blast, and that evening I am able to deliver the bike to the customer. You might have a week to do a small task. Whereas I normally have a day.

[Steve]

The passage is not a jet. It is not acting as a meter. It is simply a hole drilled to allow gasoline from the bottom of the float bowl to get to the brass pickup. That brass pickup IS metered.

That depends on the bike.

I have not noticed any particular trends related to model or year, but I have seen some carbs that had tiny holes at the bottom of the bowl passage, others have been wide open. I have seen some carbs with open "choke" pickup tubes, others have had a small hole at the tip.

It does not matter much which one has the metered hole, or even if both of them are metered, as long as both of them are not wide open.

.