Running lean

[Bigge_al]

Thanks to everyone for posting responses I have read and read and have pieced together information from one post to the next. I have been popping a vaccuum cap off, have a popping on deceleration, very little color of cinnomon plugs and sputtering on first start up take off. The combined knowledge of everyone leads me to the conclusion that I may be running lean so tomorrow I will be turning each screw a 1/2 turn CCW. I will let you now the results within a few days.

[81xsproject]

If it's lean enough to stumble and pop, I would say save some time and go a full turn.

[henri]

High end problems

Hi,

This is my first post but I have gotten a wealth of knowledge off this site. For the past two years I have been trying to restore an xs 11 special. I got it back to a running state but I am having problems. That is why I checked on the running lean post.

The bike is stock except for a K&N filter inside the OEM airbox and a four-in-one exhast system, which according to me and many others do not need rejetting.

The problem is the idle mixture screws were not in the carbs when I started cleaning so I don't know what the factory setting should be. In the repair manual they say it is factory preset, but 1-1/4 from a lightly seated position is a good starting point.

I did that but the idling is very erratic, it pops lightly now and then while idling, and I know from previous experience that the idle circuit is running lean. I had a leaking float and repaired that, followed the steps to get the float levels EXACTLY the same, 3mm from the top of the float bowl on all carbs, but the bike seems like its running out of petrol at high revs, backfires when I close the throttle and all plugs are burning a very white. I have also synchronized all carbs with a vacuum gauge.

I have checked and re-checked and I know the levels in the float bowls are correct. The only thing I can think is that fuel is not flowing into the carbs at a high enough rate because I don't have that octopus thing on the bike, but the atmospheric breathers are plugged into the airbox and sealed tight.

Can somebody please give me an indication what the average factory setting is or a reasonable starting point to start synchronising and what else I can have a look at.

Thanks

[mro]

1 1/4 turns out s a good starting point.
Set idle to about 1000 rpm and sync the carbs.
Reset idle as needed during sync.
After sync, adjust pilot screws resetting idle as needed.
(I do em by “ear” while watching a tac)
Re-sync carbs.

mro
BTW, If you use the clear tube method to adjust the floats, the bike has to be perfectly level first or they will all be off...
I just us a micrometer, 23 mm for BS34-III, 25.7 mm for BS34-II
Float level affects all RPM ranges

[clcorbin]

BTW, If you use the clear tube method to adjust the floats, the bike has to be perfectly level first or they will all be off...
I just us a micrometer, 23 mm for BS34-III, 25.7 mm for BS34-II
Float level affects all RPM ranges

I'm just jumping in here as I have had/am having some of the similar problems:

How do you tell if you have a BS34-III or a BS34-II? And could you explain your float height setting procedure in more detail? I THINK I am setting them correctly, but...

[Larrym]

Detail/options...

Clint,

Something to look at:

http://www.xs11.com/forum/showpost.php?p=61929&postcount=12

If you don't have the calipers then here's more options:

http://www.xs11.com/forum/showthread.php?s=&threadid=17287&highlight=float+height

I believe that the easiest way to ID the different carbs is to look at the inlet air horn:

BS 34 III's have four round openings inset into the front and the BS34 II's have only three:

http://www.xs11.com/forum/showpost.php?p=249062&postcount=25

[clcorbin]

Big surprise, I have the dash II carbs. I have a very nice Brown & Sharpe digital caliper sitting in it's case in my shop. I never THOUGHT to use it to set the float height! I'll use it this weekend. My ruler method got them close (and most importantly, on the rich side of the curve), but I still need to fine tune them this weekend.

[mro]

Pic, 79 BS34-II carbs



The BS34-III's pilot screw is down inside, while on the II's it sticks out.
There is supposed to be a "cross-over" set of carbs with some features of both but I've not yet run across them.


mro

[mro]

Pic BS34-III

Taken right before I removed the cap over the pilot screws.



mro

[DGXSER]

The animal exist

I hae personally seen the mixed up carbs where they have the crossover to feed the pilot jet from the main, and yet the mix screw down in the tower and the vent through the fourth hole in the inlet bell. Snookered me for a while.

[cywelchjr]

I suspect mine are the mix type (although I have not opened them since they work so well), as I have the older style bowl with the bolt coming straight up in the middle just like my 400 which does have the mix type carbs with the hidden mixture screw AND the plug over the pilot jets with the cross drilled hole. I'm guessing they have brass floats as well (at least the very very similar ones on my 400 do, and both are early 80 model manufacture dates as well.

[DGXSER]

The set I worked on had plastic floats (perhaps a PO swapped item, not sure).

All of the 80 model carbs have the straight up the center of the bowl drain plug. Only the 81 model year float bowls got the side tap drain plug with a seperate drain hole.

But then, that was also a swap on those carbs as they had the 81 bowls.

[henri]

Lean at High Speeds

Hi MRO,

Thanks for the advise. I have two xs11's. The other one is the 1.1 '81 model which have the carb with rubber floats and four holes in the back, but its in a sorry state so I pulled the carbs to compare. I am starting to think the fourth hole replaced the atmospheric pressure inlet pipes found on the older models, but I could be wrong.

Anyway, I found a leak around the left atmospheric adapter on the airbox. A big leak at that since it broke off but was sitting in such a way I did not notice since I have checked it before. My mistake, I think that is what is causing the problem.

I have a spare upper half of the airbox where nothing is broken which I have installed now. I got calipers with a depth measurement from the hardware shop and will resync tonight.

Will let you know what the results are.

[Larrym]

Hole Theory

henri,

That 4'th hole in the inlet air horn of the carbs serves as a vent for the float bowls. I think of it as letting the air out of the empty float bowls as the fuel enters and hopefully stops filling with fuel when the floats push the needle against the seat.

The vent on the earlier models was a separate orifice between the carbs 1+2 then 3+4. The orifices were joined together with a Tee which then connected to a fuel line. The fuel line then ran up to fittings on the factory airbox.

Either way, if these vents become plugged the standard symptom is that no fuel enters the carbs even when the fuel tank petcocks are opened.

Sounds like you've got a good grasp of how things are and work.

Welcome to the site and I'm sure you'll be riding that superbike soon.

[81xsproject]

The set I worked on had plastic floats (perhaps a PO swapped item, not sure).

All of the 80 model carbs have the straight up the center of the bowl drain plug. Only the 81 model year float bowls got the side tap drain plug with a seperate drain hole.

But then, that was also a swap on those carbs as they had the 81 bowls.

Somewhere there is some pics I took of one of the morphadite sets of 1980 G carbs. My set had typical 80's bodies, but the cross passage from the main jet tower to the pilot tower and rubber plugs to block off the ends of the pilot towers. They also had brass floats (again, maybe a PO change). Everything else was 80's; recessed mixture screws, integrated bowl vents, push in seats, etc., etc. If you look at the exploded view of the 80G carbs on the yamaha parts site, it shows all of these things as stock.