Yamahaha XS650 Idling crazy high.

Question

I just picked up a 77 Yamaha 650 that wasn't running when i got it.

Got her running by taking the carbs completely apart and soaking them overnight in some carb cleaning solution... Cleaned the rest of her up, changed her oil and filter and gave her a kick and she started.

Now what's wierd is that she's idling at 3K RPM when sitting still.

I checked the jets thinking maybe somebody replaced them to run higher but both are actually sized down to run leaner. (122.5 instead of a 130 for the main jet and a 25 in the pilot jet)

Once i get her up and running she runs great, but just doesn't want to chill out and idle,..

However, if I put the choke about mid-way 'on' she'll calm down and chill at 1200 RPM,.. Almost seems like somebody put the choke on backwards,.. Because when its 'on' (down) she calms down and when its 'off' (up) she races...

Any thoughts?

Answer 1

A stuck float maybe?

Answer 2

I've got a bike of the same vintage with CV carbs. It sounds like an idle air mixture adjustment along with the idle speed.  My factory manual has the following instructions.

1.  Loosen the throttle cable(s) so that both butterfly cranks are resting on the idle stop screws.  At this point there should be enough slack in the cable(s) to do the next step.

2. Back out both idle stop screws until they don't touch butter fly crank  Then turn them in 1 1/2 turns.

3. Turn the idle air screws all of the way in, then turn them out 1 1/2 turns.

4. Start the bike and let it warm up, about 10 minutes.

5. Begin on one carb by adjusting the idle air s***w until you achieve the highest idle speed, then back off by 1/2 turn.

6. Repeat with the other carb.

7. Disconnect the right plug and adjust left carb idle to the point where the engine just barley runs.

8. Repeat that process with the left plug and right carb.

9. Shut the engine off and let cool.

10. Adjust the throttle cable(s) so that both butterfly cranks open at exactly the same time.

Hope this works for you!

If you need more info, send me an e-mail.

Answer 3

Some typical conditions which can cause those symptoms are

*Intake manifold air-leak

*Sticky  ignition advance unit

*Valve clearance set too tight

Air leak is a likely suspect on any bike that age.

The Half-Choke ploy improves things because it compensates for the excess air with the extra fuel it causes to be added to the mix.

Good Luck with it.

They are great bikes & you'll really enjoy it once sorted out