i was looking at a 12a fb today. it drove fine, is suppose, but when i opened the hood, i noticed there was a hose going from the front for the blue air cleaner can to a place near the bottom of the engine.

or rather, i noticed that this hose was disconnected and alsmost totally disintigrated.

what does it do?

 

That's that hot air pipe. It takes warm air off the exhaust manifold and pipes it into the intake when the engine is cold. I think it's there to help keep the engine running when it's cold. Mine is off and it runs just fine.

 

ive never had mine on and ive never had a problem with cold starts, althought it never gets below 0 here

as long as u let the enigne warm up u shouldnt have a problem with the eingine dying under load.

 

I didn't have any trouble in cold weather after taking mine off. If you are going to run w/o one, you might as well remove the flapper assembly in the air cleaner. It's only an airflow obstruction.

 

I did that and as an added bonus it got rid of an annoying buzz/rattling noise.

 

I noticed that rattling too. I never really opened it up to inspect, but it sounds like my "flapper assembly" is what rattles like no tomorrow too.

What is it for? And how do I remove it?

 

There's a thermal-spring in the air box that keeps the valve open when it's cold and it closes the valve once it gets up to temperature. Taking the valve assembly off is pretty straight forward. Take the air box off the carb and you'll see.

 

That is the carburetor preheater hose. It keeps the carb from icing up in cold/wet weather. It's actually a good thing to have for driving in cold weather. I doubt that it's presence causes any appreciable restriction of the intake air, personally. But I do know about the rattling being annoying, fortunately the flapper on my RX7 doesn't rattle like the one on my Courier.

 

Whats the consequence from removing that flapper thingamajig?

 

You have no choke. =P

 

Different flapper man, we're talking about the one inside the airhorn not on top of the carb.

 

Ohhh, allright...

In that case, I'm guessing the thermal spring closes the flap when it's cold so you'll only draw in air from the hot air hose.

Silly me =P