BS34's

The BS 34 is a simple but often misdiagnosed piece of equipment . Continual flooding is just one result with many causes .

Incorrect float height . Simple enough , correct it .
All to often the novice will attempt to make up for other causes of flooding by bending the tab down onto the needle valve so far that no fuel will leak but also no fuel will flow . A general rule of thumb is if when upside down and the float adjustment tab is just resting on the needle valve adjust so that the float arm is parallel with the float bowl to carb body parting line . This only works if the floats have not been previously mangled .
Soaked , heavy or soggy floats .
even Nitrile floats have their service limits and susceptibility to modern fuels and alcohol content . If a float is suspect place it in a jar with fuel and compare it with the other three or a known good float . The difference will be obvious .
Worn needle valve . Seems obvious , replace .
The damage from constant contact with a needle seat will show as a definite ring around the Nitrile rubber tip . This just won't work . However in most cases the best cleaning agent for even the most green and ugly needle valve is simply your fingers and a bit of mineral spirits . The problem with this repair is its only half of the sealing element .
Dirty , worn or damaged needle valve seat . Simple enough ,replace .
Simple yes but not always the cause . A needle valve seat can be brought back to life with a little ingenuity . Remove the needle valve and leave the seat in the carb body for now . Find a drill bit whose shank , not drill , just fits in the seat . Cut the shank off the drill and chuck it up in a drill motor . Go over to a grinding wheel and attempt to reproduce the angle of the needle valve Viton/Nitrile tip on the exposed end . Finish this pointed down onto the side of the wheel . The reason for this is we are building a make shift valve seat cutter and using the grind marks as cutting teeth . Turn the shank around and do the same to the other end only this time the angle should be around 15 to 20 degrees . Those of you that have ground valve seats get busy as I explain the rest . Take a q-Tip and a bit of scotchbrite and either by hand or in a well controlled cordless drill and clean the valve seat . By hand take a few turns with the 15 degree end of the shank in the seat and observe the results . If you can see a definite bright ring all the way around the seat you're done . If more work is needed it may help to stick a bit of fuel line over the shank and use that to turn the shank . If that doesn't work by all means get out the fine valve grinding compound and use the drill motor . The seat was wasted anyway all you can do now is waste time . Do the same with the other end of the shank and attempt to establish the seat . This takes very little pressure and happens usually very quickly . Problem is after all this you may still have the problem and the needle and seat despite initial observations were not the cause .
The often over looked needle valve seat O-ring .
Oh this one still gets me on occasion even though I have the McMasters part # written on the toolbox
Buna-N Shore A: 70 -35° to +250°F 9262K627 $2.94 per Pack of 100
Viton® Fluoroelastomer Shore A: 75 -40° to +400°F 9263K565 4.26 per Pack of 25
Sorry BTK in particular and Kawasaki in general but when I can get them at these prices you can not compete .
When you can undo the needle valve seat retaining screw and plate and the seat falls out it's pretty obvious that the fuel isn't getting past your needle and seat . It's going around the seat . Replace the O-rings and be happy . Don't cut them on installation , use a bit of grease and they should press in firmly . Verify that this is your dimension and install away .
Testing your repair .
After a carb clean of any kind I place an auxiliary fuel source at least three feet over the carbs and tip , bump , vibrate , shake and last but not least reproduce their on the side stand angle for several hours under that fuel to verify that there are no further leaks or overflow . As little room as we get to install these things I know I don't want to do it twice .

That's about it , other than all parts should be clean prior to reassembly and if you get this far without me boring you or setting yourself on fire we did ok .

~kop

cool advice, how about will only run with choke and dies with throttle?

Everything has been cleaned, twice. Any ideas would be much appreciated.

I'd love to here more about cleaning the pilot jets and removal of the pilot jet cpas on the later bs34's cause that one was a real bitch for me. I had to drill it then use a screw exctrator to pull those suckers out.

For both of you I have something coming but sry not tonight . It will have to wait for the weekend .
I'd like to sift through the trash that is my writing and give you the details as best I can .

~kop

And let's not forget that all BS34's are not created equal. There are several different models with very different pilot jets and emulsion tubes/needle jets.

The design principles is the same in all BS series carbs including BS40 on GT750 Suzuki's

If the motor dies without choke, it means that there is not enough fuel getting through one of the circuits - probably the slow circuit (a.k.a Pilot jets).

Most likely are blockages in the bypass holes. Those are the tiny holes just visible at the edge of the butterfly.

Check out http://pinkpossum.com/GT750/carb/BS40carbs.htm. That page relates to the carbs on a GT750 but the others are similar. There's a picture halfway down that shows the slow speed circuits.

I always appreciate the extra knowledge.

Thanks Kop looking forward to the info.

I'll take a peek at that other info to teazer

No worries Jay, I wrote it for the GT750 crowd, but much of it applies to the other BS carbs.

There's some good info on the XS650 boards too.

Mark Salvisberg (sp?) from Factory has/had a nice little cheat sheet on setting up CV carbs in general. It's here:
http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,cv,high_rpm_engines.html

I have not tried that on our old clunkers to see how well that process applies, but he knows more about jetting than the rest of us combined.

There are several different models with very different pilot jets and emulsion tubes/needle jets.


Include some XS750 and 1100's

Thanks Kop. Despite the fact that I may be switching off of the S34 on my GS this information is great. Will help in some areas to get my up in running for spring and then new replacements as the money allows. Especially if big Rich's GS500 carb experiment proves successful on his 450.

Gary