Mikuni BS34 Has Me STUMPED!

Hey All,

I've been working on this easy, basic, and fairly simple KZ1000P for over 2 years now and am feeling like a first-grader. I have a new head, pistons and rings, exhaust pipes, and have rebuilt the carbs (9-10 times now!) and still can't get the thing to idle. Cylinder 1 and 2 simply won't fire.

They are connected to the correct coils and have perfect blue/purple spark
The valve clearances are perfect with compression of 150 all around
The carb vacuum lines are all plugged
There are no air leaks at the carb mounts - when I spray starting fluid around the carb mounts nothing happens. When I spray into 1 or 2 they fire. Also, I have sealed the carb mounts to the head with liquid gasket and I tighten the clamps onto the carbs as tight as possible.

Something to note: when I start with full choke only cyl. 3 & 4 run. After a minute of warm up I can close the choke and start to lightly rev the motor. At that point cyl 1 & 2 exhaust pipes start to heat up, so they seem to run when "on the needle" but not on the pilot jet.

Here's the BIG CLUE that I can't figure out: When I place my hand over the intake of carb #1 or #2 they start to fire (idle speed increases) and when I pull my hand away it's soaked in gas. Also, when I turn the pilot screws in or out on carb 1 or 2 nothing changes. I keep them all at 2 1/2 turns and they have new O-rings.

HELP!!!!!!!!!!!!! and thanks in advance.

For starters put the airbox back on. The bike won't run for crap without it. Plus a stock filter.

zeus.mtsac.edu/~cliff/storage/gs/Mikuni_...Rebuild_Tutorial.pdf

The link it to a carb rebuild tutorial. If you haven't done all the steps as detailed then you probably still have dirty carbs.

Thanks for you response.
Yeah, I used to put the carb to airbox boots back on with stock filter before I would try and start, but its a real pain and it didn't make a difference, cyl 1 & 2 still would not run.

BTW, I loved that tutorial and followed it to the letter when I did the 1st, 2nd, 3rd, etc. rebuild to these carbs. I practically have it memorized now.

I have used carb cleaner in a can and high pressure air many times to confirm that all the interior passages are open. Also, I have soaked and used the air to ensure all the jets are open as well. Those carbs look like new inside and out!

The only thing that seems to make sense is a major air leak somewhere between the carbs and head, but none to be found. These carbs have no vent tubes either and all four vacuum lines are capped.

. . . when I spray starting fluid . . . into 1 or 2 they fire.

Indicates failure of mixture getting into the carb bore via the pilot circuit.

If applicable carbs ---



Good Fortune!

Not sure if this is your problem or not but the BS34 "choke or starter" circuit starts at the bottom of the float bowls and 1 and 2 are the first to clog. With the float bowl removed you can see where the enrichener tube enters a casting in the float bowl. At the bottom of that casting is a very tiny jet. Just looking into the bottom of the float bowl you'll see a hole that goes down at an angle and toward that casting. A carb cleaner straw will fit that hole nicely and you should be able to squirt a good stream down into that hole and have it exit the bowl in the enrichener casting. Rarely does just squirting clean that jet/passage way. I usually have to run a small guitar string down into the casting to punch a hole in the crud. Sometimes it's clogged pretty solid but the guitar string will eventually go through. Once you get the guitar string to open the jet a few squirts of carb cleaner, from both directions, should clean it nicely.

Plus 100 on the float bowl. If you fill it up with fuel you should see the fuel rise in the well the tube goes in to. If you don't, you need to clean it out as jdvorchak advises. Also, the tube itself is easily clogged and needs to be checked. I just went thru this myself and found, after several "cleanings" the tubes were clogged. I used a single strand of copper wire but a guitar string might be more effective.
Good luck,
Jim

I concur with the other guys; make sure the choke tube is open and also the passage in the float bowl.

Be sure to remove the pilot jet and hold them up to a light to be sure the orifice is open.

Some people try to clean the carbs by spraying carb cleaner through the body instead of soaking in carb dip but that doesn't always get the internal passages clean. You gotta make sure the pilot circuits are clean or the bike won't run at low speed.

I think you fellas have the answer. I never did soak the carbs, just lots of carb cleaner and HP air (on may occasions). I've been reading that most of the modern carb dips can be weak and waste of time. What are your recommendations and what about lacquer thinner, acetone, etc.? THANKS!

The Berryman's professional chem dip is very similar to their old formula.
I compared the ingredients to a can of the good stuff that I have.

When cleaning your carburetors, did you remove the pilot plugs & air screw plugs and install new o-rings afterwards?

I use the Berrrymans dip but to be honest it will not clean a clogged pilot jet or that starter jet in the float bowl. I left a set of jets in the dip for 48 hours and still had to run a guitar string through them. I will say the dip will clean the emulsifier holes nicely and the internal passages cast into the carb body. The carbs do look pretty when you take them out of the dip tho...

Honestly I rarely dip the carbs. I can un-gang them and with a fresh bottle of brake cleaner and a guitar string I can do an entire rack in just a few hours. But that is me and I do lots of carbs every month. I like to say to my friends, after the first couple of dozen carb racks it gets easier.

martin_csr wrote: The Berryman's professional chem dip is very similar to their old formula.
I compared the ingredients to a can of the good stuff that I have.

When cleaning your carburetors, did you remove the pilot plugs & air screw plugs and install new o-rings afterwards?

I've heard good things about this formula - 0905.

Berryman's professional chem dip is a chlorinated cleaner & I think the key ingredient is methylene chloride. Their brake parts cleaner has a higher content of the stuff, but fewer other ingredients. Both products are for metal parts and probably attack plastic & rubber

Methylene chloride is toxic & easily absorbed into the skin. It's also volatile, so don't breathe the fumes. Wikipedia says there have been 14 deaths of bathtub refinishers in the past 15 years because of poor ventilation & improper protective gear.
The other ingredients in Berrymans may reduce the volatility. not sure.