1981 XS1100 Carb Troubles

[jwoell]

I’m having a carburetion problem with my XS1100 and I was hoping to get some advice from all you experts that have been running these bikes much longer than I. I recently rebuilt the carburetors on a 1981 XS1100 Special that had been sitting for a few years in a shed. The bike ran fine before it was put away. After putting the carburetors back on the bike it ran fine without the air box attached (as long as I had the choke on) it fired right up on the first attempt actually and ran quite well. The problems started after I put the air box on. As soon as I did, the bike barely ran at all. It would idle relatively normally, but then as soon as I gave the bike any throttle at all it would bog down and die. I tried getting the RPMs up and simply couldn’t make it happen. The bike seems to be running extremely rich. I have a pretty decent amount of experience rebuilding carburetors both on cars and motorcycles and I used rebuild kits that came with the same stock #120 main jets and #42.5 pilots jets that I was told are stock for this bike. I dipped the carburetors and they were very clean when I reassembled them all passages clear and all (no shortcuts taken). Oh, and I put in a brand new air filter at the same time that I rebuilt the carbs. So is there something I am overlooking as far as troubleshooting this problem? I’m just wondering if anyone has seen something like this before in these bike and is there a relatively straightforward way of getting the mixture back to where it should be. It seems to me that with all stock carb parts the mixture should be much close to stoichiometric. Oh and I didn’t change the float levels at all from where they were at before the rebuild in case that’s something I should look at. Just looking for some ideas of where I should go from here. Thanks for your help.

[randy]

A couple of thoughts:

The 'enrichener' plungers (choke) have a rubber tip. Are the tips dried, cracked / leaking fuel into the airstream?

The pilot screws - did you clean out in there, or are the original metal plugs still there? They might need attention.

Are the floats actually floating, or are they sinking?

You should have changed needles and seats, so re-set the float levels.

Take a search through the tech tips for carb related posts, should find your answers there.

Oh, and don't use words like stoichiometric, Prom will be on your case like white on rice.

[Snow]

What rebuild kits did you get? If they are K&L, the jets that came with them are suspect at best

[jwoell]

Thanks for the response Randy.


The rubber caps on the enricheners all seem to be in good contdition with no cracks or anything and they're still very flexible and not dry at all. As far as leaking fuel into the airstream, I don't know how they could be, but I'm not ruling out anything at this point.

As far as the pilot screws, I did pull them out before the carbs were dipped and I was sure to remove the little rubber o-rings that were in there too. They were replaced with new screws from the rebuild kit. The ports were clear as well.

The floats are not sinking at all. They float quite nicely. I did change out the needles and seats in the float bowls, I guess I had assumed that by not tampering with the floats from where they were at before I started the rebuild, that might be a good place to start. I'll go back and make sure they're where they should be.

I guess I'm not sure who Prom is (this was my first post). Hopefully I won't get picked on to bad for the stoichiometric thing Any chance you could elaborate on that?

Thanks for your thoughts!

[jwoell]

Actually Snow, they were K&L rebuild kits. Do you think the jets could be that far off in those kits? If so I guess I could just go down to the local dealer and just get new jets if you think it could help.

Thanks.

[Snow]

They will most likely cause it to run at least badly - K&L is like a four letter word around here when talking about jets. The rest of the kit is fine, just the jets are off...in the rich direction...

[Ljay40]

jets are easy to clean save yourself some money
throw your old jets back in and see how it runs before you\go buy new ones

[John]

Uh Oh

Originally posted by jwoell
I dipped the carburetors and they were very clean when I reassembled them all passages clear and all (no shortcuts taken).

Did someone say "I dipped the carbs"? Did you use the caustic type of carb dip? If so, then the throttle shaft seals and the enrichener plungers are most likely ruined. They will swell up and basically dissolve when you use that stuff, unless you have removed EVERYTHING from the carb bodies.

[jwoell]

Thanks for your suggestions!

Well I followed your advice and went and picked up some new pilot jets from the local Yamaha dealer. Wow, I can't believe how far off the ones from the K&L rebuild kits are!! The bike went from hardly running to being totally driveable and very strong!! Took it for a spin around the block yesterday (even though it was raining) and was very impressed.

Just wanted to say thanks for everyones suggestions from this thread and many others!