Newbie Questions

[Da-Bubble]

I recently bought a 79 XS11 Special. It starts and runs but it has a backfire at low speeds. It will idle just fine but when I'm riding slow it pops and sputters. Then once I rev it it takes off smooth as can be. I was messing with it the other night and I decided to start it and feel the pipes. The number one cylinder's header wasn't even warm at idle while the others were instantly lava-hot. I am planning on pulling the carbs and rebuilding them. I've seen the $12 kits on partsnmore, but the $18 kit from the Yamaha shop had a ton more parts (new jets and stuff). Which kit should I buy and where should I start to diagnose the #1 cylinder issue?

[Ken Talbot]

Before you buy a rebuild kit with jets that will probably be the wrong size, just try giving the carbs a good cleaning. You may tear up a float bowl gasket or two, but gasket paper is cheap and you can make your own. Your dead #1 at idle could be as simple as a plugged orifice in the bottom of the float bowl. This orifice supplies fuel to the low speed circuit, and it can get plugged from the cr@p in the botom of the bowl. You might also have a broken pilot air mixture screw in carb #1. Read all of the carb articles in the technical section, and use the search engine at the top of the page to look for 'float bowl orifice' and 'broken pilot screw'.

[skids]

Re: Newbie Questions

You might want to tweek the pilot screw for that carb just a bit. First, look at the spark plug to see any evidence of fouling. Then note carefully how many fractions of a rotation you adjust the pilot screw so you can undo the adjustment if necessary. If the plug showed excessive carbon or was fuel fouled, clean the plug, install it, and try about a quarter turn clockwise for the pilot jet. On the other hand, if the cylinder isn't getting hot while using the starter jets (aka "choke), there is a good chance that the jet in the bowl is plugged.

[moonshine]

same problem

I also have a 79 special. The previous owner had let some play mech on his bike and had 1, 2, 3, running lean and 4 running rich. Try setting piolet screws at 1 1/4 turns out, check to make sure they are in sync after you give carbs a good cleaning. This solved my problem.

[Da-Bubble]

Thanks everyone for the help. I want to work on it but it's been 110 degrees here the last few days so I've been staying indoors as much as possible!

[HobbyMan]

Kind of off topic but if its too hot outside, Bring your bike into your living room. Just tell everyone else it is a coffe cup stand