XS11 Special Needed Infomormation

[MPittma100]

I bought a 1979 XS11 Special a while back (had a new XS11 Standard in 1978). I have done some work to the bike and have some questions as a result of my endeavor.

First question is about carburetion. These had smaller than OEM jets in them (122.5) and the needle valve was set to the one lean position. All info that I have seen shows 137.5 jet and standard needle position for this model? Why would someone have changed this or did it possibly come from Yamaha this way?

Second question is about the decal on the inside of the left side cover. One line reads "Exhaust Emission Control system:" "Engine Modification".
Another line reads "Fuel Specification - Gasoline Grade Regular (Leaded).
My question here is does anyone know what "Engine Modification" indicates and is anyone addressing the "leaded" issue for the fuel requirement when fueling your bikes?

Thanks, Mike P

[crazy steve]

If you have the 'correct' carbs on the bike, that's waaay too lean.

What I suspect is the PO has changed the original carbs for a set of '80-81 type, in which case that should be right or maybe even a bit rich. The carbs have to be jetted for the year of the carbs, not the bike, as there's internal differences. No big deal if that's the case, but it will make a difference if you need parts for them. Or possibly it's been fitted with a DynoJet kit; I believe their jets are numbered differently from OEM.

As to the 'leaded' fuel, don't worry about that either. Run the bike on a quality regular (or mid-grade if you get pinging) and you'll be good to go. The reason for the call-out of leaded is in those days, unleaded had a considerably lower octane, which is generally not the case anymore. The 'usual' problem with running unleaded (in those days) in a 'leaded' motor was damage to the valve seats unless they were hardened. The XS has hardened seats (as do all aluminum-head motors AFAIK), so that's not the issue. Leaded fuel had been gone for years, and there's been no reports of seat damage that I've heard.

The 'engine mod' line is just a EPA thing, ignore it....

[MPittma100]

Thanks for the reply Crazy Steve

Thanks for the info. I went ahead and replaced the smaller jets with the 137.5, checked all the other jets, and moved the needle jet to the normal position. Floats were way low and caused fuel to come into the airbox - adjusted them to proper height and cured that problem. Adjusted/synchronized all four and engine is running/idling/accelerating well. I have not looked at the spark plugs to verify mixture, but will do so.

Another factor: This bike had 10K miles ahowing on the odometer when I purchased it and the past owner believed it to be accurate. General condition of bike indicated this also - except for one issue. First time I rode the bike, I noticed a "flutter" when accelerating. Ran a compression and cylinder leakage test. Reults were no compression and 100% leakage on number 2 exhaust valve. Pulled head and found the valve head cracked almost all the way around the circumference. It appeared to have failed possibly by being run too lean or it could have been metal fatigue. Hard to say, but that is one of the reasons that I looked at the carbs.

Thanks again, MP

[XS1100_OEM4ME]

79's

Here are some good pic's of what 79 carbs look like and, what seams to be a fair price on a set if you have the wrong one's. Its a bid, so who knows, you can always sell the ones you have and recoupe some of the $$$$ if these help

http://cgi.ebay.com/ws/eBayISAPI.dll...m=360407885953

[XS1100_OEM4ME]

Gas

I am sure you know, but if you had gas in the airbox you most likely have gas in your oil Change before you ride

Thanks for the info. I went ahead and replaced the smaller jets with the 137.5, checked all the other jets, and moved the needle jet to the normal position. Floats were way low and caused fuel to come into the airbox - adjusted them to proper height and cured that problem. Adjusted/synchronized all four and engine is running/idling/accelerating well. I have not looked at the spark plugs to verify mixture, but will do so.

Another factor: This bike had 10K miles ahowing on the odometer when I purchased it and the past owner believed it to be accurate. General condition of bike indicated this also - except for one issue. First time I rode the bike, I noticed a "flutter" when accelerating. Ran a compression and cylinder leakage test. Reults were no compression and 100% leakage on number 2 exhaust valve. Pulled head and found the valve head cracked almost all the way around the circumference. It appeared to have failed possibly by being run too lean or it could have been metal fatigue. Hard to say, but that is one of the reasons that I looked at the carbs.

Thanks again, MP