Bike only runs with choke out

[CoreyCorey73]

I recently bought a 1980 XS Eleven Special. The guy that had it let it set up a year before I got it. My problem is that it only runs with the choke out and it backfires really bad. As soon as the choke is pushed in it dies. I have took the carbs off twice and cleaned them, but it did not help. Does anybody have any suggestions as to what it might be? Thanks for the help!

[TheDjost]

The pilot jets are not adjusted properly. The choke compensates for this.

First make sure you got the idle jet passage cleaned, and that you can see through the pilot screw holes with the screws removed(no broken tip jammed inside). Then replace and adjust. If you don't have a colortune, you'll have to go by ear. Turn them out until you get steady idle when warm and no choke. You got it pretty much on when the RPMs go straight back to idle and stay put when you rev the bike to 2500 RPM. If the revs hang then you are running lean... back out the pilot jets half a turn(no need to turn off bike, just use a long screwdriver) at a time until you get smoth operation. If you can't get it to run right(all the way out, and still has problems) then something is wrong with the jetting, the engine, the carbs, or the exhaust.

For this to work, make sure all the slides are preforming properly by looking at them. Just run the bike without the air box in.

[skids]

The likely culpret is that the pilit jets are clogged. You can clean them with a guitar string or similar. The center holes are TINY. Use in-line filters to help prevent clogging. The other holes that could be suspect are in the ventouri bores, on the top, near where the throttle plates "close."

[CoreyCorey73]

Thanks for your help but where are the pilot jet adjusters? Are you saying that they can be adjusted while the bike is running? Thanks!

[CoreyCorey73]

Also I remember when I had the carbs off the motor and the bowls off at least two of the pilot jets did not have screws in them. I looked on a set of old carbs I have and those pilot jets did have screws in them. Could this be part of my problem?

[TheDjost]

The pilot screws are on the top of the carbs, just over the throttle butterflies. One for each carb. If you did not have those off, then that is sure toi be your problem. The crud you blew through the pilot JETS got jammed up in the pilot SCREWS.

-Justin

[skids]

The pilot SCREW on top of the carbs is mostly for idle mixture (+/- fuel). There is a hole directly beneath it. The other three holes on the top of the ventouri bore by the throttle plate is the outlet holes from the pilot jet. There has been considerable discussions about whether or not the 80 models were capped below the pilot jets in the float bowl area. It seems that Yamaha may have used-up existing 1979 model carbs on their 80 models. If so, the pilot jets will be plugged below the pilot jet and there will be a cross bore from the main jet bore to supply fuel to the pilot jet. Also, if that is the case (older carbs in 80 model), the mains will be larger to account for supplying fuel to both the pilot jets and main jets. Another difference will be that there will be a need to use a vent tube to the airbox. The newer carbs do not need the vent tubes because the vent is supplied on the perimeter of the inlet bell. To recap, yes, you do need the caps below the pilots, if your carbs fit the above descriptions of the 78/79 carbs. The newer carbs are not threaded to accept the caps.

Originally posted by CoreyCorey73
Also I remember when I had the carbs off the motor and the bowls off at least two of the pilot jets did not have screws in them. I looked on a set of old carbs I have and those pilot jets did have screws in them. Could this be part of my problem?