High idle after warmed up

[Trgglynn]

Hey, it’s a nice day to ride in Oregon!
I went on a ride and noticed my hot idle isn’t what it should be. When I start the bike cold, let it run, push the choke in the idle will be set at 1200 RPM. However when I ride the bike and stop with it in neutral it wants to keep the idle up at 3000 RPM.

It seems like it’s kicking up the idle to charge the battery, but it never seems to come back down. This is with a new Yuasa battery

Any ideas on this?

 

[Jim]

It seems like it’s kicking up the idle to charge the battery, but it never seems to come back down. This is with a new Yuasa battery

The engine, alternator, carbs.... have no means of bumping up the idle. I'd suspect air leaking into the intakes or carbs.

 

[Trgglynn]

The engine, alternator, carbs.... have no means of bumping up the idle. I'd suspect air leaking into the intakes or carbs.

I was wondering about that. I brought the idle down to ~1200 with the motor hot. I assume when I try to fire it up cold, if it won’t start that will be a clue.

Do you know where I can source some of the choke slide seals for my Mikuni carbs? I probably need the intake boots too. I’m having trouble locating a good source for either of these though.

 

[Jim]

Availability changes as supplies become available and get used up.
That and I don't know what bike you have, let alone what carbs you're running.

Have a look at this list of suppliers. Maybe you'll find what you need in there.

https://www.xs650.com/threads/parts-suppliers-for-the-xs650.68549/

 

[Trgglynn]

Availability changes as supplies become available and get used up.
That and I don't know what bike you have, let alone what carbs you're running.

Have a look at this list of suppliers. Maybe you'll find what you need in there.

https://www.xs650.com/threads/parts-suppliers-for-the-xs650.68549/

Sorry, I should have been more specific. I have a 1981 XS650. I believe I have BS38’s. They’re vacuum carbs.

 

[Jim]

If they're the stock carbs, they're BS34's

 

[Trgglynn]

If they're the stock carbs, they're BS34's

Thanks for refreshing my memory, i think you’re right.

 

[steve zodiac]

Are the carb tops chrome or aluminium?
Bright chrome=34mm
Aluminium=38mm.
For replacement carb boots, you can't beat jbm great product, with excellent service.

 

[Trgglynn]

They are BS34’s. I ended up ordering some new boots and some “throttle caps” for the choke rods. Is there any other common places to get an air leak?

 

[grouchie77]

Butterfly shaft seals if I'm not wrong.

 

[Trgglynn]

Butterfly shaft seals if I'm not wrong.

Are you talking about where the choke shafts slide in? I don’t have a ton of experience with these carbs but they have the whole vacuum slide deal. Which part are you referring to when you say butterfly?

 

[grouchie77]

The shaft that is actuated when you twist the throttle.

 

[Trgglynn]

The shaft that is actuated when you twist the throttle.

Ah copy, I didn’t even think about that one duh.

 

[grouchie77]

When the bike is warmed up and idling, squirt some WD-40 at various suspected leak spots, if the idle changes, it'll help you narrow down the source.