BS 34 carburetors

650Skull

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Do you remember what jetting for that needle position
Is it a US Version or European / Oceania

Thinking out loud about Needles and Markets I got the impression that the version being non adjustable being emission laws
regulated and leaner. there is a lot of variables
US bikes were setup leaner and the law prohibited changes.
So if I get it right the designer are designing 2 different objects with different internals
Object A and Object B He has the task to get it working and running on respective markets
Normally he has little interest in matching these between markets
Because very few are going to drill out and adjust needle as a customer in the US
by warranty and legal reasons back then on a new bike.
Not that common either ship bikes between countries then.
I think the designers order was do the setup and test it manufacture and ship.
Perhaps taking the parts from another bike setup
My guess is that the US Bike runs leaner than the other for the same jet.

More Air ( Extra holes ) is no problem if you can adjust Needle and other
But it is dangerous if you cannot adjust

Jan i have an Oceania and Canadian model. They both have the 5lX11 needle and 336YO needle jet.

I have translated the Japanese 4E3 Standard model parts file, the Japanese used for their market and the Euro Standard model, (80/81), with the Adjustable needles, to English. I will post it up when i get home. Haven't got my external HD with me.

This parts manual has the recommended jets for these Jets/needles but the jet sizes are basically the same as the US used. I run 132.5 Main and 130 Air jet
 
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Jan_P

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So a 135 main Jet can be to large .I have had the feeling it lacked a little on top .
Am I the only one having it with essentially stock setup..
Perfect on middle but to rich according to plugs.
Will an oversize main jet give that symptom. Lacking oooomph on top ?
I have kept it rich to avoid overheating but is it to rich ??
And yes I will service the suspect electrics
 

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4E3-3W6-3U6 TEXT copyright.jpg


This is the only translated version of a BS34 parts file showing part no's for the adjustable needle and 336YO jet and the pilot screw.

I'm not really a carb guy. You will need to use the information and work it out from a base point. 5Twins probably has the answers but he also say,s you have to work the different jets from a base then go up and down in sizes till the engine tells a story then go up or down one till it is happy.

Seems that because the US was the main market and they had such strict EPA mandated emission laws there is no reference to the Pilot screw or a part no. No parts manual has that info and using the info from this parts file, 5Twins did a search and came up with an alternative Mikuni BS carb Pilot screw from another carb. ..............This fits the BS34 carbs for the XS650
1 Pilot screw replacment Part 1.jpg
 
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Jan_P

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Started servicing
The Idle mixture screw was set differently the right was 1/3 of turn more restricted.
The washers against the O -ring is not there .Unless both fell out during the work I don't believe so
The O rings is flat and hard ..
I have 2 sets carburetors
Since I was uncertain how it looked inside I tried to open the first set carburetors
and there the washer was in on the first carburetor the other screw I cannot at the moment get out .
The slots has been destroyed on both mixture screws so someone has tried to adjust those carburetors. Slots are looking like an X. Twisting .Inwards is rather OK But outwards difficult maybe even impossible
the one I got out worked with max pressure inwards on the screwdriver and with effort loosening it.
I applied light oil over night WD-40 type .. Since it can be moved inwards ---perhaps I can get it out eventually
If so the plan is to get new O -rings and use the washer from the set that have them. For now.

If there is any trick loosening Slots now looking like an X feel free to give advice and
Also on the O -ring Size I have seen it here on the forum and perhaps find it later on

Plan B 2 new sets as in Above. 12R -14105-00
 

5twins

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Many drill in too far when drilling out the cover cap and hit the top of the mix screw. This damages the screwdriver slot. It usually only gets worse when you try to adjust it because the screwdriver won't grip it well enough. For what they cost, I'd just get some new ones. They come with new metal washers and o-rings but if you just want to replace your o-rings, a 1mm x 3mm size works.
 

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The slot on the top got worse and worse ..and I had to do something else
Perhaps all know how but put it here can help someone

I Used a small drill hand held machine trying to drill a center hole for smashing in a philips bit or so
But since the top was uneven the drill wandered off to the side making the hole a bit off center
Could not get the Philips screwdriver to hold
So I opted to drill another hole 180 degrees from the first one
I slant the drill slightly inwards and take care not hitting the aluminum hole edge
I then have 2 holes ..and if pushing the drill carefully against the metal in between the small holes using it as a mill
I then get an elongated slot and there i Got god Grip on the screw. With a screwdriver

The hand held machine is risky. So be careful .But If one has a shop machine and clamping it
The method with two holes or three removing the in between metal and it can be a way forward.
Being soft brass and being caerful not breaking the drill

Cannot see any washer though which was the reason for taking it out
I am now down 2 O-rings and one washer
Have to make some hook se what still is down there Letting it soak some more in light oil
And reevaluate.

Edit :::: upon clearing the workbench ..I found the washer It was sitting on the magnetic tip of a Philips screwdriver that I had used to pry in the hole to loosen things I had not noticed it sitting there coming out
 

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Jan_P

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Did find one more small washer ..it had turned 90 degrees and was sitting higher up in the hole with little larger diameter
pos 5 in # 23 -Thank You for that

Flashlight and Magnifying glass I could see it. 3 found so far .. in two sets I am not good at these small " Watch Repair " Sizes items

The O-rings are hard and if you ask me looks more like Fibre washers ..But can still be rubber. and hardened over the years.
Could not find the sets to buy unless expensive .. so I have ordered 4 O- rings from Holland 2 spare
The Slots are fine for the Screwdriver .
Seems as a little water have come down there a little white corrosion .Going to polish that
The spring is not mint but it is not moving that much ill try it. Have them in oil now.

I had the carburetor in a small tub ( Plastic Lunch box ) Using an old toothbrush and solvent to clean
it.
That was a big advantage ..when the small springs and balls flew out from the choke axle.Installation.
And clips for the needle. And so .It landed at the bottom of the box instead of the floor
Where perhaps the missing Washer is .

Should have thought of this before the tub is needed for the cleaning but I have taken it out for the adjusting ..use less solvent
Keeping it in there ..and ...when adjusting saves time trying to find small objects that fallen out or as the springs ejected.

Have 135 main Jet and moved the needle to No 2 slot ..Can still be to Rich se what happens ..
Come the O -rings the last setting and then wait for the spring
Still a few months ca 2- 3 before bike comes out and the wiring service happens
Thank you for the input.
 

5twins

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As I mentioned earlier, if it's never been done, you should consider replacing the butterfly shaft seals. You can remove and inspect the condition of the outer one on each carb without having to remove the butterfly plate and shaft. On the left carb, remove the cable arm and spring to expose the seal. On the right carb, remove the e-clip and plastic washer on the outside end of the butterfly shaft. The seal needs to be very soft to work right and they harden up with age. You can judge how hard it's become by pinching the seal between your thumb and forefinger, changing it's shape from round to oval. If it's soft and good, it should be easy to pinch and make oval shaped.
 

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As I mentioned earlier, if it's never been done, you should consider replacing the butterfly shaft seals. You can remove and inspect the condition of the outer one on each carb without having to remove the butterfly plate and shaft. On the left carb, remove the cable arm and spring to expose the seal. On the right carb, remove the e-clip and plastic washer on the outside end of the butterfly shaft. The seal needs to be very soft to work right and they harden up with age. You can judge how hard it's become by pinching the seal between your thumb and forefinger, changing it's shape from round to oval. If it's soft and good, it should be easy to pinch and make oval shaped.

Thank you Sir
I did replace them while rebuilding 2 years ago. I had problems getting the valve plate ( brass disc ) in and out
I will take a quick look so I did not put the seals in backwards by mistake
While they are on the bench
I did not take out the idle jets then - In hindsight a mistake because the Clymer manual said they should not be touched.
Being factory set. I have it written down on paper how many turns so I can get the same setting if needed.

There was dirt in there ---- and perhaps one missing washer ---flat O -rings ... uneven setting right / left
A bit start problems on right cylinder. Have good feelings so far about this.

Speaking of mistake I put the main jet in and tightened the bowl screws. But i did not take out and clean the jets
Probably not dirty but never the less. Have to open it again taking them out. Do it To be certain
 

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By "idle jets", I assume you mean the mixture screws. There is no adjustment on the actual jets (main, pilot, needle jet) other than changing them to a different size.
 

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By "idle jets", I assume you mean the mixture screws. There is no adjustment on the actual jets (main, pilot, needle jet) other than changing them to a different size.
Yes Yes its the language difference ..the mixture screw
 

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Pilot screw..... ............Common name, mixture screw................ but in reality the fuel and air is already mixed before it gets to the pilot screw outlet
 
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