New eyes find wrong carbs

[3Phase]

I got the seat back today from B & H Specialties and it looks great!

After a nice summer of riding, ol' Columbo started to run like the carbs needed some TLC and the new iridium plugs were running a tad on the lean side. I bought some new, larger, main jets and dug into the carbs for the first time since the beginning of summer, before the Yosemite rally.
It's been fun!

Thanks to the extended tour through the carburetors' casting numbers, needle jets, jet needles and just general jetting - compliments of and my personal condolences to Crazcnuk - I tore into the carbs with a new vision and a much better idea of what type of parts really ought to be inside of a bank of 1980 XS1100G Standard carbs.

Okay, I was wrong!

Now I can't find any carb body casting numbers to help me identify the carbs. Where, exactly, on the carb body casting is the part number? The only place I haven't been able to look is underneath the carburetor rails that hold the carbs together in one bank and those screws are screwed quite firmly in place.

According to the Yamaha factory manual these carbs are set up like a 1980 Special with #110 mains all the way across and 5GL16 jet needles instead of 5IZ7 needles. I didn't spot the #110 jets on the #2 and #3 carbs when I cleaned them up because the main jet faces and markings were almost completely obliterated by corrosion but the jet orifices themselves cleaned up and work fine.

I used someone's tip of polishing the brass jets, the tubes and the the needles until they look like shiny new parts. I finally managed to find a part number on the needle jets (emulsion tubes) but I've never seen the part number:
(Mikuni logo)300FJX-2

Yes, it's all run together like that with the leading Mikuni logo. They're supposed to be 300 X-2 jets but I don't know if the FJ in the part number is significant or not.



Needle jet (close-up under magnifying glass) cleaning lower row of large air bleed holes




XS1100G needle jet (close-up under magnifying glass) cleaning upper row of small air bleed holes





The needle jet orifices are not worn




Needle jet and main jet cleaned and polished




The new main jets I picked up originally to try to go up from the #110s in the #1 and #4 carbs are: 2 ea #115, 2 ea #117.5

After finding the #110 mains in #2 and #3 carbs I bought 2 ea #120 mains but I did not know at that time that I had the 'wrong' jet needles.

I put the #120s and #117.5s in the carbs and installed the bank of carbs. The bike started up and ran fine cold but the carbs are way out of tune and it's too late at night to do anything but shut down and pick it up where I left off tomorrow!


Regards,

Scott

[egsols]

Sounds like you have SG carbs, see this link...

http://home.wanadoo.nl/web5/xs1100/T.../carbspecs.htm

The link specifies that the SG used BS34III 3J6-00 carbs with 110's across all 4 and the 5GL16 needles whereas the G used the BS34III 3H5-00 carb with 115's on 1 and 4 and 120's on 2 and 3 and the 51Z7 needles.

What's weird is the Yamaha parts list shows 120's and 125's on the SG (3J6 carbs).

I also tried to find a stamping on mine but couldn't, just a faint labeling on the side of the diaphram housing. Another thing, checking the Yamaha site is that the G's ran the 3H5 type III carbs with the SG, H, SH running the 3J6 type III's.


I can kinda see someone changing all the jets to 110's but to change the needles to match, that's a tough one. Could it be that you actually have a set of Special carbs or maybe a set off an H?

I have a set of 300 tubes in the garage, if I get a chance I'll did them up and check the number.

[skids]

Sounds like you have SG carbs, see this link...

http://home.wanadoo.nl/web5/xs1100/T.../carbspecs.htm

The link specifies that the SG used BS34III 3J6-00 carbs with 110's across all 4 and the 5GL16 needles whereas the G used the BS34III 3H5-00 carb with 115's on 1 and 4 and 120's on 2 and 3 and the 51Z7 needles.

I wouldn't put 100% faith into that chart. I tore into two sets of E-model carbs that had 210 pilot air jets installed (not 180).

[boyat68]

That chart is simply what is suppose to be in the stock mentioned models, not what you find as many of our members re-jet due to modifications. After 28 years, anything is possible. My 80 G has stock parts as mentioned in the chart and page 10-20 of the Yamaha manual and I kept it that way when I replaced my jets during re-build.

[tarzan]

I have rebuilt the carbs on three different SG's here in my area.All three had
110's in all four carbs.Two of the bikes I know came that way,I dont know for sure on the other.So I dont know if the dealer here installed them when they were new for our particular altitude or if they were stock from the factory.I suspect they came stock that way though.I too read about the 110's and 120's talked about in the manual ,but havent experienced it yet though.

[3Phase]

I think I have the Special SG carbs instead of Standard G carbs. I can't find any numbers on the carb bodies themselves so I'm going by the jet needle part number and jetting. I have no idea how they got there and neither does the last owner. The original owner is dead and I refuse to disturb him.

I haven't been able to access the Yamaha parts catalog for a few days now. It starts to load from the "Member Sign-Up / Login" and "Proceed to Parts Catalog" page, then just hangs and never loads the Select Model page.

Oh well. The carbs on my bike are definitely BS34III late-model carbs with no rubber plugs in the pilot jet towers. The bike runs great so far but needs a synch. I left the carb synch tool (Motion Pro mercury-type with 4 tubes) over at a buddy's house so I have to run over there and get it before I can synch the carbs. At least it's not laying enough black smoke to cover a WWII aircraft carrier convoy!

I found an interesting thread here last night about the BS34II carbs in the '78 E model providing the best fuel mileage of all the XS11000 models and using #210 air jets with #42.5 pilot jets instead of the #180 air jet. Naturally I can't find that thread this this morning.


Off to grab the carb synch tool, then back at it!


Regards,

Scott

[boyat68]

3Phase:

When I did my carb job, (80g) I looked all over those carbs for a number but did not find one. I also had the cross drilled pilot to main tower that took a rubber plug to force the fuel supply up through the main across to the pilot. The 80 year had two types of carbs according to TopCat, drilled and non drilled, with the drilled being in the first part of the year. My understanding is that the G and SG bodies are the same except for the cross drilled and the open pilot tower, and of course the mains and jet needle with the jet needle probably being a different taper.

[3Phase]

Aaaaaaaahhhhhhhhhhh!!11wun...wunwunwun!

Pwned!

Okay, this thing is scary-fast now. Even with the 750 final drive I almost wound up hanging onto the handlebars with my legs a'flappin' in the breeze behind me.

YES! <pumps arm> the new jets are working just fine.

3Phase:

When I did my carb job, (80g) I looked all over those carbs for a number but did not find one. I also had the cross drilled pilot to main tower that took a rubber plug to force the fuel supply up through the main across to the pilot. The 80 year had two types of carbs according to TopCat, drilled and non drilled, with the drilled being in the first part of the year. My understanding is that the G and SG bodies are the same except for the cross drilled and the open pilot tower, and of course the mains and jet needle with the jet needle probably being a different taper.

The non-cross-drilled pilot tower was what I meant by 'late model' BS34III carb.

I'm not entirely certain that a cross-drilled 1980s carb is actually a BS34III and not just a BS34II casting with some new fashion accessories - different float bowls and cold start jets; plastic floats; rubber-tipped float needles and press-in needle seats with o-rings; different needle jets and jet needles.

There are some non-obvious internal differences (the pilot screw, seat, and metering orifice) but I can't see any obvious differences in the carb bodies themselves between a BS34II carb body and a cross-drilled BS34III carb body except the mods for the plastic floats and the press-in float needle seat.

Well, that and the lack of a part number anywhere on the carb body casting.



Right now I have to pull the carbs back off. #2 cylinder is cold at idle and low RPMs and doesn't begin fire until I get get into mid/upper RPMs and the mains start to take over. Just in case it wasn't a plugged pilot circuit I swapped spark plugs and plug wires, tweaked the pilot screw on #2 carb open a few turns further and pulled a compression check. All cylinders are between 145 and 149 lbs. I tripped the pooch; pilot's blocked on #2 carb.



At least I have my new seat to look at as I work on the carbs!




Regards,

Scott

[3Phase]

Paranoia will destroy ya'

The carburetors were fine. I took the bike out and just ran it for a while instead of pulling the carburetors and everything cleared up.

The new #117.5 and #120 main jets make a noticeable (sotto voce: There's an understatement if ever I've written one) difference in performance around town and getting on the local freeway.

I'm taking a run out to Arizona this morning to check the fuel mileage on the open road. I have to see if the engine gulps fuel and if I can keep my big thumb out of the carburetors.



Regards,

Scott