BS 34 carburetors

Jan_P

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Haha
Im gonna tell a true story a Major Fumble
I was out in the shed doing work at the workbench
Had Things in the vice concentrating on that I had a PET bottle with water sipping water now and then
Warm summer day 30 C or so nothing you down under would notice

But at the same workbench i had a Plastic bottle with White spirits ( I think it is so in English ) solvent for cleaning brushes and so
Concentrating on the work I took the wrong bottle drinking

Plupp plupp plupp --> Something is wrong here ...something warm and oily
.. Pprrrttt -- ttt and flushing the mouth with water
I did not swallow any .. But I did get to hear it from Friends now and then for a long time..
 

Jan_P

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Still stumbling between 2 - 3 k and Float Valve did not close or operate as it should. in Pri Position
Flooding again this time the petcock worked stopped In ON Position
So there is a carburetor problem.
Can it be the new shit Fuel ?? Alcohol fuel or is it just dirt ?? .. Did not take the carburetors down yet because the season is over more or less.
Buit will do it in coming weeks
One very experienced man i met today and know
said they have had problems On older cars.
 

Jan_P

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Yes Sir
I do believe they have less dirt growing tomatoes than I had in the Float Valves
The red is sealant for the Petcock and the black can be the petcock rubber internals of the one not Closing
World record perhaps ??


IMAG0135.jpg
 

Jan_P

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Cleaned and installed stock jetting and stock needle position
AND --- Still stumbling a little between 2-3000 drove ca 120 km yesterday

Starts and idles fine ca 1500 ..Runs smooth up to 2 k .The sync did that I did not know An XS 650 could runs so smooth.
riding 2000 rpm giving gas it chokes and then rev up stumbling a little ---Above 3 k cant notice it.
Either the spark is weak or the mixture is wrong . I feel it is to rich and thinking about going down on Pilot Jets
The air filters are somewhat old.
Still not read the tech section so there can be more adjustments to do They are synced and cleaned.
Wiring is substandard.
But putting it out here .Does that sound wrong go down on Pilot. Jets ,,
It is possible with carbs on the machine.

edit ?? Remove Air filters getting more air Testing --- if that makes any difference ..perhaps
 
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Jan_P

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Talked to the professional the proprietor at the dealers today.
Very nice people ..
Cant remember anything he has been wrong about
The main focus first will be cleaning air Jets and adjust the Mixture screws.
I don't think those are far off..
But have to admit have never in my life cleaned an air jet that I can remember.
I don't have compressed air so lets se how I do it ..
According to the Tech manual the Pilot air jet is removable and if I get it right here pilot should be the one at
2 .--3 k rpm
AS they say about computers this can be a RTFM fault
Read the f*****g manual
Got lost perhaps never had more than a handful carburator problems and when one appears failed to stop look for electric faults. Lets se.
 

5twins

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Yes, I was going to mention the air jet. It's a way to fine tune the idle circuit because changing it doesn't have as big an effect as changing the pilot jet itself. There is also an air jet for the main and midrange circuit but you can't change that one, it's pressed in .....

BS34BellMouth.jpg


I think you have the European model and carbs so you will probably find a #130 air jet in there. In the States, we got 135's, two sizes larger, and that made our idle circuit a bit leaner. Whatever size you find in there, going smaller will add less air and make the circuit a little richer, going larger will add more air and make it leaner. A small round main jet was used as the air jet, a Mikuni N102.221 .....

N102.221.jpg
 

Jan_P

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Thank you Sir
I feel optimistic about this ...
Season may be over before it is sorted. Temperature is dropping.
 

Jan_P

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Yes Sir

probably find a #130 air jet in there. In the States, we got 135's, two sizes larger,

Are those the same jets as used for main jet if so I can have something at home already

Had # 130 s in there Could not see any major dirt in them .or when using a match sharpened with a knife
pretty much clean wood coming out.

But what I did notice upon inspection was that the Air Filters perhaps is past best before
Bordering to need to replace .. Have not payed attention before.
Need to think about it Maybe at bit to restricted on the air jet .But rejetting is not the solution if a clogged filter is the reason.
It affects other ranges also and machine performance.
Obviously the mixture can be off if the filter is dirty.

can those be washed 25 euro a piece perhaps not so much but if possible wash why not try
For once I have the seals intact and they are not broken otherwise. Holes or so.

1665508485216.png
 

5twins

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No, the air jet is not the same style as the main jet used in your BS34 carbs. Your mains are the large round main, the N100/604 type. The O.D. is too big to fit in the air jet hole .....

MainsCompared.png


You can probably remove the old, worn out foam from your filter "cages" and re-wrap them with new foam. UNI sells bulk sheets of filter foam. It would probably cost about half of what new filters would.
 

Jan_P

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Scored one NOS filter on line on the Cheap side

Put the other ones in a bucket with warm water over night and washing machine powder
Yanking it so the dirt goes outwards held with the water covering that side
The water got dirty so something is coming off.
Changed the water and doing it again ..
Perhaps ill try the dishwasher machine powder might be more powerful.
 

Jan_P

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Maybe Solved
Cleaned the filters and
came out OK 6-7 on a scale to ten can be difficult to be sure if they are cleaner all the way through
looks better on the picture than in real life
Cleaned the Air Jets

Rock and Roll -- Throttle response
Did miss a little on full throttle suspect the petcock
Tried to keep it between 2 and 3 k on the short test ride did not notice any stumbling.

To be honest if it is solved it was mostly a rookie mistake --- Dirty Air Filters.
Did not look so bad but should have replaced them sooner.
Could not se into the fixed Air jets used a Nylon Fishing string and solvent poking around
And had the removable jets in a jar with solvent for some time.

Filters
IMAG0137.jpg
 
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Jan_P

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NO Still not solved.
Its better
It is better but still chokes upon throttle from 2 k and then stumbles a bit .. not much but still. to - 3 k and then disappears when rev up
I can live with it for now .. and a while.. I am getting tired of taking it off and on.

Since it got better a fair assumption is that it is air / mixture related for now.

Have never had a XS 650 running so smooth under 2 k .Cruising in town
Synchronizing did that. I believe
The throttle response Hooligan revving maxing out is almost perfect 8 on a 10 scale.
I don't need that to be perfect. Dont drive that way ( With this bike dont want to trash it )

It misses at times at top rpm I do believe that to be the sh*t Petcock . I do believe I can sort that out
Needle is in stock position can move that.
That is rpms not used for many years and driving style not used.
New air filters is needed
Better carburetor adjustment ( Tech Manual )
And a smaller Air Jet
I believe I will start looking for another Carbs set and do the job on that having a bolt out bolt in setup
Perhaps taking it to the shop that have Ultrasonic cleaning or so.

One set on the bench works in progress. and Another in the bike
Ignition Lock is a factor
As the wiring
Had 2 Boyer sets on it and can go to points If needed.

It feels as to rich mixture there 2 - 3 k Season is more or less over I can have it like this for a while
It is not perfect but I can ride.
 

5twins

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Well, if you think it is too rich, you would want a larger air jet, maybe try the 135s like we got in the States. But if your bike is 100% stock, you shouldn't really need to stray much from the stock jetting. Carb problems would more likely be something plugged or clogged inside them, or the dirty air filters like you found.

Yes, having a spare carb set is nice. I'm currently running spares on both my bikes. The spares on my '78 are there while I overhaul the originals. They're working well so I'm in no hurry to swap back. I'll get the originals done up over the winter and put them back on next spring.
 

Jan_P

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Well, if you think it is too rich, you would want a larger air jet, maybe try the 135s like we got in the States. But if your bike is 100% stock, you shouldn't really need to stray much from the stock jetting. Carb problems would more likely be something plugged or clogged inside them, or the dirty air filters like you found.

Yes, having a spare carb set is nice. I'm currently running spares on both my bikes. The spares on my '78 are there while I overhaul the originals. They're working well so I'm in no hurry to swap back. I'll get the originals done up over the winter and put them back on next spring.

Yes Sir
Have a connection with Mr DogBunny he seems to have the 135 jets.
The exhaust is a bit more open .otherwise stock
And I have one filter coming in looking for the other one in the coming winter.
This is what happens not doing it systematically trying a quick fix. Keeping costs down
A lot of extra work and at the end the costs is the same or even higher sometimes.
Have not had time to read the tech section Because of an estate division in the family ...taking all the time.

Another carburetor set bolt on would help .. it can still be the wiring that needs to go.
Again trying to use things to long and getting into trouble and at the end still ends up doing what should have been done long ago.

It is an old habit from bikes that is uncertain will run one more year. . Don't want to spend money on it trying to fix it.
 

5twins

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If your exhaust is freer flowing, I would think you need to go richer, not leaner. When you were inside the carbs, did you pull and clean your needle jets? They have rows of tiny holes down their sides that let the air in to mix with the fuel. If they're plugged, the bike will run rich .....

StockNeedleJets.jpg


You could experiment with needle settings, that's free. Try one step richer and one step leaner than where you're set now, see which runs better or improves things. This may not totally cure your 3K stumble but it should tell you if it's from being too rich or too lean.
 

Jan_P

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No Sir and thank you.
I did not take them out .. I know almost nothing about carburetors and has been poor on the .Read up.

The sideways holes is not cleaned in the. needle jets

It is not much more open exhaust than stock and I have had the same setup many years.
+ 10
Without the stumble
I first noticed it last year coming from higher speed to lower in a village.

So it may well be dirt somewhere I did try to clean with solvent and Brushes
But I did not take those out.

Season is almost over and I still have the estate division to do.. Family matters . So it may be over for this season.
I ll se if I take carburetors out Mr DogBunny has the 135 air jets that would be interesting
to test.
 

5twins

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The air jets are easy to change with the carbs still in place, just take off the air filters.

Let me tell you a story about the needle jets in my buddy's 1980 carbs. His bike has pod filters and a freer flowing exhaust yet with stock jetting, it was still running very rich. That was very odd, especially for the lean-from-the-factory BS34s. He swore to me up and down that he had cleaned them very well and replaced most all the parts inside. Well, when I finally got a look inside them, I pulled the needle jets and found them all black and gummed up along the sides. All the little air holes were plugged, lol. He never touched them. His floats were also all messed up. He had switched to plastic ones but tried setting them to the brass float spec, lol. Needless to say, that didn't work very well. The carbs would randomly start belching fuel. His plastic floats were also aftermarket and junk. So, he sprung for genuine Mikuni brass replacements, we cleaned the needle jets all up, re-jetted for his mods properly, and the carbs are good now. So, you need to pull your needle jets out. Chances are they're getting dirty along the sides and those little air holes are plugging up. They could be the cause of all your issues.
 

jpdevol

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And for the uninitiated: the needle jets "tap" out from the main jet side into the venturi. Just remove the main jet and its brass washer, thread the main jet back in (without washer) and give it a (hopefully) gentle tap to start. An 1/8" wood dowel can also be used as a punch. Some pre-soaking in penetrant lube doesn't hurt if gummy in there.
 
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