Mikuni BS34 Has Me STUMPED!

I'm re-cleaning mine now. How do you make sure the passage from the starter tube to the fuel screw is clear? It has some right angle turns so not sure a guitar string will work. I'd rather not have to un-gang and dip them but I will if that is what it takes.
Also, I've ruined some parts by leaving them in the Berrymans dip too long. How long do normally leave them?

Always ungang the carbs. The fuel transfer tube O-rings are the ones most prone to deterioration because ozone gets to them among other things. Do the job right the first time and be done with it.

ThatGPzGuy wrote: I'm re-cleaning mine now. How do you make sure the passage from the starter tube to the fuel screw is clear? It has some right angle turns so not sure a guitar string will work. I'd rather not have to un-gang and dip them but I will if that is what it takes.
Also, I've ruined some parts by leaving them in the Berrymans dip too long. How long do normally leave them?

With the bowl off you will see the passage way where the starter tube, attached to the carb body, goes. Down at the bottom of that is the tiny jet so a guitar string goes right down there. Yes there is a tight turn at the bottom that connects to the interior of the float bowl but the jet is in the vertical part. Now I caution you. You can poke the string down there and you can sometimes feel the clog and twisting the string a little will push through. BUT you have to squirt your cleaner into that hole from both directions as it will sometimes re-clog. So squirt both directions a few times before you call it clean.

Anybody tried boiling the carbs rack along with the removed float bowls and jets for a few minutes in plain water (except for the rubber diaphragms which should not be boiled) ?

Good Fortune!

I have boiled them before and it does a good job but use only distilled water. Plain tap water has calcium and as soon as you pull the parts out, the water dries and leaves the calcium behind. I used to boil jets that way and it will loosen the gunk but you still have to use a guitar string to push through. Also it doesn't always get the emulsifier holes clean.

One thing I've learned from cleaning carb racks. THERE ARE NO SHORTCUTS!

Believe me if there was an easy way to clean those tiny jets we'd all know about it.

Guitar strings are CHEAP and last forever. Find a local music store and ask the sales person for the skinniest strings they have. An entire set of strings is usually about $6 but you can buy just the High "E" for a couple of bucks! Another couple of bucks for a can of Brake or Carb cleaner. Don't get throttle body cleaner. I've heard it doesn't play well with the old rubber. Brake cleaner is seems to work the best for me. f

A couple of tips I've learned over the years:
Even if the O-rings look good, replace them. You actually ruined them when you took it apart.
NEVER put on an O-ring without first lubing it with Vaseline or dialectic (silicon) based grease. YOU WILL ruin your brand new O-ring if you try to put it together dry.
Keep penetrating oil, like PB Blaster away from the carbs. It will destroy any rubber in a matter of seconds.
With Mikuni CV carbs the float needle seats have an O-ring around it and it is bad! Replace it.
Mikuni and Keihin sometimes have a rubber or plastic plug over the pilot jet. Pull that plug out and use a well fitting screwdriver to remove the jet. Sometimes they are stuck. Let it soak with some brake cleaner if it doesn't unscrew EASILY! Don't force it as it will break. Also use your heat gun to help loosen. The good news about gasoline residue is that it loosens quickly with heat. .

Since we seem to talking about carbs a lot I have to say something about tools. These screwdrivers, from Harbor Freight, are the best tools I've found for working around the bikes. They don't say they are JIS but they are. It has the #2 crosspoint (Phillips) head that is used everywhere on the bike especially the carbs. Also the straight blade screwdrivers have heads that will perfectly fit any Mikuni or Keihin carb jets.

www.harborfreight.com/32-piece-screwdriver-set-90764.html

Keep the Snap-On and Craftsman screwdrivers away. They will round the head of a Phillips or slot screw.

jdvorchak wrote: With the bowl off you will see the passage way where the starter tube, attached to the carb body, goes. Down at the bottom of that is the tiny jet so a guitar string goes right down there. Yes there is a tight turn at the bottom that connects to the interior of the float bowl but the jet is in the vertical part. Now I caution you. You can poke the string down there and you can sometimes feel the clog and twisting the string a little will push through. BUT you have to squirt your cleaner into that hole from both directions as it will sometimes re-clog. So squirt both directions a few times before you call it clean.

No. I know how to clean the fuel bowl. I'm talking about the passage from the bottom of that tube to the pilot screw. In Patton's pic it is the Fuel to Starter Jet that goes up to the pilot screw.

The starter jet passage is what I'm referring to. They both go to the pilot screw but the starter passage and jet are often neglected when cleaning the bowl.

Could try also adding the following carb cleaner spray patterns ---





Good Fortune!

Yep. II have those printed out and am referring to them while I work on my carbs.

Hey Gents,

Well, I'm finally writing back to report. Found someone who recommended BOILING the main body of the carbs (after separating and dismantling of course!) for about 20 min and it WORKED. I now have all four cylinders firing. Still, cyl #1 seems to be spitting back through the carb occasionally. I'm gonna put the boots/air filter back on and run it with some Seafoam. Also, have some carb sync parts on order and will adjust both butterfly and richness ASAP. Thanks for all your advice!

Well done. I'm glad you let us know how it turned out. I'm fighting the same issue myself but have resisted tearing the carbs down completely. It sounds like that is what I am going to have to do.
If one cylinder is backfiring it is probably a bit lean. After the boots are back on if it is still doing it try backing the pilot screw out a 1/8 -1/4 turn at a time.