Carb change for XJ 900 1984 to later 36mm ?

Hello from Brittany, France- I have a collection of XJs here and have a carb problem on one of them- I am trying to find information on whether it is possible to put the 36mm later model carbs on my'84-
I have started the bike with them on, but it will only run on half choke-
Is it possible to rejet them or make a good set out of the old and the new?
Many thanks- and any one looking for parts of XJs- I have multitudes!

Ian

 

Hi Ian,
I am currently re-building an XJ900(motor at least) and have swapped all the 35mm mikuni jets/needles to a set of 36mm mikunis from a FJ1200.
(had to manufacture a new cable attachment though and swap the bowls about so I wouldn't recommend FJ1200 carbs unless you want some extra pain fitting them)

Haven't started the motor yet but I reckon it couldn't be 'that' much different... surely! So it's possible, I reckon

What was the carb problem, btw?

 

Hi - ( used to live in Perth ) thanks for the quick response-
I have a set of 36mm carbs and could change all the jets- I believe there are quite a few differences in slide configuration as well as fixed jets in the carb body-
I had the same idea, to change everything over, but wondered if anyone has done this?
My 35mm has been mutilated by someone and one of the carb bodies is broken around the diaphram-

 

Are you quite sure the Carbs are Mikuni 35's?

My 900 runs Mikuni BS-34's.
I have several "Naked" Bodies.

I also have some 900 Carb Jets to sell.
I know they're 900.
Would have to look at the sizes though.

Rick

 

Sorry, Rick - you are right they are 34s- there are no markings on them to indicate that, but they are the originals-
I have checked out the 36mms, and they have different needle jets and I assume the needles as well-
If I change all the jets over from the 34mms to the 36mms along with the slides and needles, would they run?
I know the starter jets are different as well, but these cant be changed- I believe
Thanks for your help - if you need any XJ stuff , it is prolific here in France.
Ian

 

I dont know if the 36's are "Bolt-on"

I'm not too sure, ... but I think the 36's were fitted to the 1200's and to use them you might have to swap the Fuel Gallery Barrels and Tees them mount them using the Rails from the 34's.

What 34 Body do you need?
I might be able to send you a Body and Bowl. Naked.
Casting with Throttle Plate devoid of Jets and other parts.

 

Hi again Rick, thanks again for your rapid response and information.
I may have confused you- I have a set of carbs off a later model XJ 900 - perhaps 1989 - (58L?) - I put them on the '83 and it started but would only run with choke-
Today, I removed all the jets and slides with needles and needle jets, from the '83 carbs to the '89 - so far, now, I cannot start it again- not sure why- I am probably creating more problems than I am solving... :roll:
The carb body I need is the right hand outer -
I would have thought they would run however- not sure what the problem is-
How would I make payment to you and how much for the body?
Thanks again
Ian

 

IF, after a brief warm-up, the Engine will only RUN with Enrichment, ... the Problem we are going after is likely to be FUEL SUPPLY.

Begin by assuring yourself that the Pilot FUEL & AIR Jets are of the right size and in the Proper Pilot Fuel and Air Orifices.

1.) Remove the Pilot Jet. Remove the Pilot Mixture Screw and its Spring, Washer & O-ring.
Flush the Passages TOP to Bottom, ... blocking-off open Orifices with a finger or a Rubber Stopper.
Flush the Pilot AIR Passage through the Pilot FUEL Jet.
Block Pilot FUEL Jet.
Flush AIR Jet through Pilot Mixture Holes. (Upper and Lower.)

Remove Main FUEL Jet and Washer.
Drive-out Center Emulsion Tube.
Flush Main AIR Jet through passage which exits in the Center Tube above the Main FUEL Jet.

Flush SIPHON Tube with Enrichment Valves Open.
Flush ALL the Jets including the Metering Jets which fill the Enrichment Reservoir.

Scrub the Diaphragm Piston Bores with ScotchBrite Gray & White.

Bench SYNC Throttles using Index Card Strip (1cm X 6cm)
The idea is to Bench Sync the Throttles for Mechanically Synced: Closed!

Install the Pilot Mixture Screws.
Pre-Set the Mixture Screws: 0.55cm "Deep"
0.55 cm's to the TOP of the Screw from the TOP of the Hole the Screw is placed into.

 

Ok cheers again Rick, will do that and report- many thanks
Ian

 

Having spent the last week trying every configuration possible with my carb swap I can tell you that I am now an XJ carb specialist...
(I have been a motorcycle mechanic for 30 years I might add)
The bigger carbs basically go straight on the early XJs, as you probably are very aware, however, I changed all the jets, springs, needles diaphrams etc to be sure, but this compounded my problem- I have now gone back to the 58L needles and just left the main jets from the earlier ( smaller) carbs-
The bike now runs clean and with a bit more fine tuning and tinkering I think it will be ok- but in comparison to my other two XJs there is no discernible difference in performance. Thats not why I changed the carbs however, it was because the previous owner had broken the side out of one the originals.
He had also plugged the carb breather tubes to each other causing a over pressurisation of the system which really had me confused for awhile until I realised what he had done.
Thanks for all the help guys.