BS34’s

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Rogt

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Hi, I have a 1980 UK Spec XS650, it has a twin tap fuel tank and BS34 carbs with seperate fuel inlets on the outside of each carb but the only replacement carbs I can find due to mixture screw problems have a central inlet, have I the correct carbs and tank ? Thank you.
 
Well the US was different than other markets, but only in the non adjustable needle/clip and cap on the idle mixture screw. I (strongly) suspect your set up is not original. AFAIK ALL bikes that had BS34's came from the factory with a joining tee and single petcock tank.
Edit: As shown later in this thread, jabbering above was wrong

DSCN3332.JPG
 
Last edited:
Rogt said:
Hi, I have a 1980 UK Spec XS650, it has a twin tap fuel tank and BS34 carbs with seperate fuel inlets on the outside of each carb but the only replacement carbs I can find due to mixture screw problems have a central inlet, have I the correct carbs and tank ? Thank you.
Click to expand...

Hi Rogt and welcome,
like Gary sez, the tank & carbs on your 1980 XS650 special ain't the ones the bike left the factory with.
The outside fuel connections say the carbs are orphans (or is it possible that the dreaded PO could have switched them over?)
As you plan to replace the carbs with stockers put a Tee on the line from the carb joiningTee to join up both fuel taps.
The twin tap tank may be from an XS650 Standard, which drops straight on and is a gallon bigger.
 
Pic.......Europ had a Standard and Specials untill 81/82..........

Brochures i have do show a Standard with a Tank with 2 petcocks and BS38's
Yamaha XS650 81.jpg prospektbild_von_1982.jpg
 
Yes so a good idea would be to post up pics of the carbs to aid positive ID The factory BS38's have separate fuel taps but they are between the carbs which have a crossover port also.
Like skull says the XS carried on, in some markets anyways with the BS38's and dual tap tanks.

A set of 78-79 BS38's

bs38 78-79.JPG
 
petcocks look like aftermarket manual petcocks on a vacuum tank?
Carbs do look like XS650 BS34's. My guess is if you look 'tween the carbs you will find where someone blocked the original fuel entry point. It would be relatively simple to cross drill the fuel passage and tap the outside of the carb for banjo's. Carb screws all replaced, someone's been in them fairly heavy. If the work is good and jetting seems reasonable they may be fine? I consider myself to be a buggared mixture screw removal maestro but others exist, perhaps find one on your side of the pond. Hint if they say I'll just use an easy out, grab your carbs and run!
this thread may be of help... http://www.xs650.com/threads/bs34-idle-mix-screw-issue-ideas-wanted.54337/
 
Some pics of the bike would help...........Have you done a vin/id for the model and year of the bike??.........Is it an import or a local dealer bike??

Its hard to tell but the side-covers look like the US78SE/79SF/80G type and there was a US Custom with the same side-covers sold in Europe as a European model
 
XS400 carbs had the fuel line tapped into the left carb like that, right carb was fed by a crossover tube between them. Someone could have tapped the right carb for another line.
 
Rogt said:
View attachment 138604 View attachment 138605
Click to expand...

Hi Rogt,
nice closeups but also pan back and show us the complete bike, dammit!
The shock angle will show if it started life as a Standard or a Special.
(That's the ONLY difference between the two that can't be changed by swapping parts around)
Lift off or side hinge seat? Points or TCI sparks? Sheetmetal or plastic sidecovers?
Those little differences help to determine exactly what your bike is right now.
 
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Thank you for all your responses, from them I think the carbs are 34's but swopped around to provide the outside connections? The actual bike has the hinged seat and tin side panels.
 
650Skull said:
Some pics of the bike would help...........Have you done a vin/id for the model and year of the bike??.........Is it an import or a local dealer bike??

Its hard to tell but the side-covers look like the US78SE/79SF/80G type and there was a US Custom with the same side-covers sold in Europe as a European model
Click to expand...

US import or not..????.............Shouldn't have BS34's........looks like you have air-box's.........34's are shorter than 38's and don't normally reach the air-box from the model you show.........anomalies!!!!
 
A vin no and i can tell you........should be between 3L1-000101 and 3L1-020000 if Euro specific

I only have one brochure for that model and it is hard to tell if it has BS34's from the Factory
 
Not a good translater......to English
CARBURETOR

BRAND .................................: MIKUNI
TYPE .................................: BS34 (3L100)
MAIN Jet ........................: 132.5
NEEDLE Jet ........................: Y-0
Jet NEEDLE ........................: 5HX13-3
NEEDLE POSITION (measured from above) .....: 3rd
STATIONARY SPRAYER ...................: 42.5
STARTING SPRAYER ........................: GS 1:30
FLOAT HEIGHT (mm) ..................: 24 mm +/- 1.0
STATIONARY SCREW (Strikes back). : 1 1/2
HEAD AIR Jet (mm) .............: 85
STATIONARY AIR Jet ............: -
GAS VALVE (NO.) .......................: 135

From the Dutch XS650 Club
https://www.xs650.nl/25-models/132-model-3l1.html
 

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