need help with 1981 xs400s xs 400s

[dfam4]

Hi all- I'm new to this forum, but am hopeful someone can help. Here's the story...

I saw an add on Craigslist for a 1981 Yamaha xs400s- "$250 FIRM, Bring a truck" I figured since I rode one back in college, this would be a good bike to start on again- it's been a few years.

I've put in a carb kit, gone through all the electrical etc. I replaced the stock airbox type air filter with K&N style air filters. Bike will start ONLY with starter fluid. Once it starts, it will run nicely. Will restart when warm on it's own.

Float bowls have been adjusted to recomended setting, valves have been adjusted, and I just installed new plugs. Plenty of spark.

Things I've noticed-

Bike will only run when vacuum tubes on the intake manafold are not hooked up- they are open to the elements and you can feel the air going in and out of the them.

When it's running, when I rev it up, sometimes, even though the throttle is back in normal position, it will continue to rev on it's own at about 4,000 RPM, and then gradually come down to normal idle RPM.

Thoughts? Comments?

HELP!

Thanks!

[Cy Welch]

Hi all- I'm new to this forum, but am hopeful someone can help. Here's the story...

I saw an add on Craigslist for a 1981 Yamaha xs400s- "$250 FIRM, Bring a truck" I figured since I rode one back in college, this would be a good bike to start on again- it's been a few years.

I've put in a carb kit, gone through all the electrical etc. I replaced the stock airbox type air filter with K&N style air filters. Bike will start ONLY with starter fluid. Once it starts, it will run nicely. Will restart when warm on it's own.

Float bowls have been adjusted to recomended setting, valves have been adjusted, and I just installed new plugs. Plenty of spark.

Things I've noticed-

Bike will only run when vacuum tubes on the intake manafold are not hooked up- they are open to the elements and you can feel the air going in and out of the them.

When it's running, when I rev it up, sometimes, even though the throttle is back in normal position, it will continue to rev on it's own at about 4,000 RPM, and then gradually come down to normal idle RPM.

It's way lean. The carbs are not really clean in the idle circuit area or their not adjusted right. You have to drill out the plug over the screws (on top just behind the rubber boot connected to the engine) and adjust them. You also may need to get o-ring and adjusting screw kits from MikesXS as well. Once the idle mix is adjusted right it will start correctly and not hang at high RPMs once warm anymore.