xs11 79 carbs

[DEmily]

IWell folks, I am driving the old girl now. It's great to finally get to ride! It runs good but it's not quite right.
I am having a problem with my carbs running rich. It seems to be mainly at idle. I have cleaned the carbs four times and have found something new everytime. The last thing I found was I had mixed up the Ts on Number three and four and had the fuel Ts in the hole for the bowl vent. The T is of course to large and plugs it's self up against the inner body of the carb. Now that I have fixed that, I am idling much better but still rich. I adjusted the floats to 27MM slightly leaner than specs, but I kept having issues so I decided to make sure the bowls were not floading.
Pilot screws have been screwed all the way in and still idleing rich. Obviously I am getting fuel from some where.

Does anyone have some sort of a diagram of the carb? I would like to find a resource that can help me understand exactly how these carbs work. I believe if I can understand how every part. port and jet works together , I will be able to figure out what is going on here.

Another question: I read a post,that talked about the new pilots jets are a bit different than the 79 pilots and will run too rich in these older carbs. I had K&L mains in them but took them out as you all informed me they were incorrect. I do still have the pilot jets that came in that kit in the carbs. Could these jets be causing me some issues? I'm thinking I shouyld clean the old ones and try them.

[Dennyz]

The K&L pilots are worse than the K&L mains. You should be able to clean your stock ones or purchase new ones a cycle shop. Get rid of that K&L crap (IMHO).

[DEmily]

Thanks DZ, I'll do just that!

[DEmily]

Hey all,

I have a question regarding the idle on these 79 carbs. When the bike is at idle, how much of the idle is determined by the position of the butterfly. Where does the idle circuit supply fuel from? Just looking over the carb it looks like the pilot screw allows air to pass to the diafragms and lifts them, giving fuel from the mains. How do the pilot jets get involved? I'm sure I'm way off here. Maybe one of you gurus can explain it to me?

[xssiveone]

Sid Hansen has a nice schematic of a carb on his page that shows the air flow pattern. Carb schematic

You asked for a "guru'... well, I'm not him but I'll try my best.

No fuel comes from the mains at idle, it all comes thru the pilot jet. From the schematic, you can see the fuel flo from the float bowl thru the pilot jet up to the idle mixure screw, and then into the air flow from the carb as it enters the engine. The idle speed is controled by the butterfly and idle mixture only. The diaphrams and slides don't have anything to do with the carbs at idle. They don't come into play until (I think) 1/2 throttle.

[sixtysix]

Originally posted by DEmily
Hey all,

I have a question regarding the idle on these 79 carbs. When the bike is at idle, how much of the idle is determined by the position of the butterfly. Where does the idle circuit supply fuel from? Just looking over the carb it looks like the pilot screw allows air to pass to the diafragms and lifts them, giving fuel from the mains. How do the pilot jets get involved? I'm sure I'm way off here. Maybe one of you gurus can explain it to me?

Here is all the info you need:

Go to www.factorypro.com

Left hand side of screen click on MC Tech.

Then click on CV Carb Tuning

Then click on engines with red line above 8000 RPM

Take 10 minutes and read all the steps and it will help you

[DEmily]

Gary & Brian,

Thanks for the info. The schematics and tuning info should be a great help.

A question about exhaust. Originally the bike had 4/1 exhaust. I replaced that exhaust with MAC 4/2. How would this effect the needed main jet size?

[sixtysix]

Since both were aftermarket, I wouldn't think it would be any different between the two, there may be a little but not that much.

Usually aftermarket exhaust and air filter will take you up a size or two, but main jets size is only critical at WOT, other than that needle position is more important.

[DEmily]

I also have after market cone filters. I have tried the bike without the filters on and still experienced the rich idle, so I don't think that is my problem.

[CMA1]

DEmily,
Greetings!
I just went through this with my 79 Special. I got rid of the Octopus, to begin with.
My pilot jets were wrong .. hadn't seen them described here before. So, I replaced those with new ones OE. Much better.
Also, the float hight was a bit tricky... I ended up at 25mm which is on the lean side, according to Clymers (25.7 ~ 1mm) and I have 142.5 mains installed (MAC 4 into 1... with open baffle[none])
It runs great now... just LOUD!!! Carb noise (EMGO cones) is awesome and the header is really,, too loud. I will change that as soon as I can afford it, but I like the 4 into 1.
Everthing seems to be in order carb wise now ... thanks to the gifted people on this site.
I had her out last wednesday, seemed ok. Now I got the damned headlight relay problem to chase down

Travel Safe. Larry

[skids]

Shoot, just rip out that stock relay and put in a switchable relay! It will pay off someday when you are in a traffic jam and your headlight is running down the battery. It is really pretty easy.

http://home.earthlink.net/~sidskids/relay/relay.htm

And here is a way to remove the reserve lighting unit if you also want to do that:

http://home.earthlink.net/~sidskids/rlu/rlu.htm

Originally posted by CMA1
I had her out last wednesday, seemed ok. Now I got the damned headlight relay problem to chase down

Travel Safe. Larry

[DEmily]

Hey Larry,

Will that's just strange. An hour ago I pulled the pilot jets and replaced them with the originals and BAMMM! Runs incredible!
No more black smoke just flat out horse power!!! I haven't even resync yet. Will do that this weekend. But guess what Larry, now my headlight relay is failing too! That is just strange. That's ok, I'll fix that. after all this bike has put me through, I can handle headlight issues.


Yes, I agree, these guys are the only reason I have this thing running. Joining this site is the best thing I did since I got this old dog! I will be a member for as long as they will have me


Just a quick not to any new xs1100 owners reading this.

Never use the letters xs and K&L in the same sentence. They don't play well together


Thanks for all the advice everyone. I'm sure I will still have more to do to her, but the BIGDOG is runnin!!!

[dntemp_ca]

Hey, Skids
After you do the headlight mod on a 78 or 79, does the switch on the handlebar turn the headlight on and off?

[skids]

I got rid of the aftermarket toggle on the 81 and installed a 78 handlebar on/off switch. The other two 78s I have are rigged with them also, stock. I think that on the 78, you can simply cut the yellow wire to the stock relay and use your headlight switch to switch them off when the bike is running, but I think the problem was that the runner lights in the front stay on. I don't exactly remember because I have had the aftermarket relays installed for quite a while.

Originally posted by dntemp_ca
Hey, Skids
After you do the headlight mod on a 78 or 79, does the switch on the handlebar turn the headlight on and off?

[dntemp_ca]

Thanks, Skids
I may try disconnecting the yellow wire and see if that works on my 78. I'm ok with the runner lights staying on....actually, converting the runner lights to l.e.d. would save some more energy. Another item for the project list for next winter!