Mikuni float bowl passages

[Guest]

I have found that with some Mikuni float bowls the part throttle passages are half way blocked. They might actually pass some fuel even after you shoot them with carb cleaner. That small passage in the float bowl that supplies fuel to the part throttle port just past the idle position of the throttle plate, work from that point till about 2500 rpm. After that time, both the idle port and the part throttle ports are no longer measurably effective because at 2500 rpm your main jets come into play. What I usually do now on all my Mikuni rebuilds, is get a 1/64th size twist dril, set the depth to not drill through the bottom, and drill out the float bowl passage. In most cases I can feel the drill "thunking" into the lower chamber as it drills through the blockage. No metal shards have ever been seen, so I know I am drilling petrified gasoline. After reassembly the carb has taken on a whole new personality where throttle response is quick and tight with no apparent flat spots. At lease not while on the centre stand. At that point I can take the bike out and test for main jet adjustments.

I have never seen a message regarding the drilling of thses ports in any forums. But after reading sooo much stuff in these forums with people searching for reasons the carbs are not working..... I have found just about 100% success rates after I drill out the passages.

I hope this note might help a few of you...

Mike...

mikestp@yahoo.com

[Steve]

Can you please post a picture of this "float bowl passage"?

There are several "passages" in the float bowl area, just wondering which one you are drilling.

.

[chuck hahn]

No way in hellll would you find me drilling on any carb passages. Thats what carb dip and proper carb cleaning is all about.

[mikestp]

No way in hellll would you find me drilling on any carb passages. Thats what carb dip and proper carb cleaning is all about.

First off... I am speaking of the float bowl not the actual carb body.

Secondly you are assuming I have not tried to clean with Carb Cleaner (Berrymans if you wish to know),or Gun Wash, Ultrasonic, wire probes.... To no avail. As I told you in the previous message, I have done this now many many times and each time I look for any signs of metal to show me I have possibly drilled into casting. And no times have I ever seen any. Do what you wish, but I am not a newbie. 40 year veteran on aircraft maint. and semi retired now. But you can continue to try and try and try to resolve off idle problems...

Good luck with that....

[mikestp]

Can you please post a picture of this "float bowl passage"?

There are several "passages" in the float bowl area, just wondering which one you are drilling.

.

There is only one passage in the float bowl on 1985-1999 Mikunis that I am aware of. A fuel pickup tube fits into it. That tube goes to the part throttle ports of the carb. I have not seen any other passage in a float bowl.

[chuck hahn]

Thats the starter circuit ( choke) tube. And i was assuming nothing, but based on your description one can never tell what a newbie is talking about. And if you soak the bowls also, all you need to do is flush the hole the pick up tube goes in with air and carb spray and use a thin wire to poke the hole at the bottom open anyway. Sounds like your over complicating trying to reinvent the wheel to me,,,and its an unneeded thing.

And if you wanna be real anal about the hole, a simple Qtip stick cleans it out just fine also.....and doesnt do any potential damage like a drill bit can.

[Nessism]

Yup, it's a choke circuit pickup passage. The idle circuit is fed by the pilot system. Fuel comes in the main jet and then branches over to pilot side. The factory service manual for the GS850 has a nice section detailing the various carb circuits, including diagrams showing how the passages connect inside the carb body.

[btbarb]

Yup, it's a choke circuit pickup passage. The idle circuit is fed by the pilot system. Fuel comes in the main jet and then branches over to pilot side. The factory service manual for the GS850 has a nice section detailing the various carb circuits, including diagrams showing how the passages connect inside the carb body.

So would drilling the passage in question be the equivalent of having your choke slightly engaged?

[chuck hahn]

no. The only way the choke can be engaged is if the plungers are manually lifted or the rubber ends are cracked and hard and letting fuel seep past. Dont friggin drill the hole out!!!! Useless and totally irresponsible drivle. Soak the bowls, use a Qtip stick to scrub the holes sides, poke the bottom hole from the bowl side, then flush with spray and air. The bottom of the bowl isnt real thick and if you slip your fuucked!!!

[londonboards]

I asked the same question in my thread: http://www.thegsresources.com/_forum...13506#poststop

and in my blog: Carb Float Bowl Question

Mine were completely blocked and I wasn't sure if they were supposed to be:



Nessism came to my rescue telling me to hammer away and make them work.

Greetings

[chuck hahn]

Fuel comes into the well via the hole at the bottom of the hole the pick up tube sticks into,,then its sucked up into the carb body and thru the starter circuit via the choke plungers. T

[btbarb]

So would drilling the passage in question be the equivalent of having your choke slightly engaged?

I re-read and see mikestp was not changing the hole just clearing it.

[chuck hahn]

yes...but its kinda wrong to suggest that the gunk needs to be drilled out when it in fact doesnt!! thats my entire point and I have a problem with what i consider hack advice. Simple dipping and rinsing WILL clear the tubes of any buildup.

[Fjbj40]

You know what? What he is saying is to use a drill bit and twist it by your fingers, this will not remove any metal unless you are not thinking. It is tried and true simple practice used in many applications. Sometimes that hole is plugged solid, no Q-tip will remove the material no matter how hard you try, grab an UNDERSIZED drill bit and voila, cleared in about 5 seconds. Then you can use the Q-tip to remove the rest because you made an opening in that rock hard ****.

His advise is a valid bit of info. But as always it is your choice to take someones tried and proved ways of doing a job differantly than what you do.

It is not hack advise, that is your opinion!

[Agemax]

You know what? What he is saying is to use a drill bit and twist it by your fingers, this will not remove any metal unless you are not thinking. It is tried and true simple practice used in many applications. Sometimes that hole is plugged solid, no Q-tip will remove the material no matter how hard you try, grab an UNDERSIZED drill bit and voila, cleared in about 5 seconds. Then you can use the Q-tip to remove the rest because you made an opening in that rock hard ****.

His advise is a valid bit of info. But as always it is your choice to take someones tried and proved ways of doing a job differantly than what you do.

It is not hack advise, that is your opinion!

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, and as Fjbj40 says, it then makes cleaning and flushing the hole properly a much quicker and easier chore.

i cant see how you manage to fit a Q tip in the tiny hole in the bottom of the choke pick up tube.........