What does a heat riser accomplish?

[tutone63]

Excuse my ignorance, but this is a question I have been wondering. What do they do? Are they essential? I have noticed the conversation on "heat riser function" and the thought occured to me...what are they for? Are they for the automatic choke? If so, how important are they? I have heard of some removing them...what would that do?

by the way, this is a purely academic question...I have no intention of removing mine at this point.




1963 Lark, 259 V8, two-tone paint, Twin Traction. Driven often, always noticed!

[dictator27]

It redirects exhaust heat through a passage in the intake manifold under the carb to warm up the incoming fuel mixture. As the engine warms up, the bimetal spring relaxes allowing the weight on it to open the valve. It can be a real bear to keep a cold engine running without it, particularly when putting an auto trans in gear.

Terry

[Mike Van Veghten]

It also warms the air going into the carburetors choke. It has a simillar spring that extends or "opens" the choke blade. This allows the choke to know when the engine is warm enough to open fully.

Actually, the exhaust isn't really redirected so much as it's forced to go...rather than take the path of least resistence thru the "other" exhaust port (2 in each cylinder head) and into the intake manifold to heat it as dictator27 notes.

Mike

[tutone63]

Yeah, that makes sense, now. I knew HOW it worked...I just wasn't sure on WHY you would want to restrict, or redirect the exhaust. But now I know. Thanks alot!

BTW...is it possible for those chokes to stick? I have this re-occuring problem with my lark that it wants to act like it is choking itself. I have mentioned this before on an earlier thread, and I was told that it was most likely a vacuum leak. I have since replaced all of the gaskets and hoses, rebuilt the distributor, and still it wants to do it...just not as often or as severe. It won't stall anymore, but it will still idle poorly and run rough. If I stomp on the gas quickly, or stop and restart the car, it will go away. I wonder if my next step is to rebuild the carb...it probably needs it anyway. Maybe its the float?




1963 Lark, 259 V8, two-tone paint, Twin Traction. Driven often, always noticed!

[StudeRich]

It really sounds like nothing is wrong with your Carb. at all!

What COULD be happening is that in Winter/Fall/Spring your climate may get cold enough to over-choke the Carb. cause rough idle, black smoke requiring 3/4 or more throttle to de-choke it, but as warmer weather comes around it gets better as the butterfly is open more when cold starting in mornings in Summer.

It would only need a choke adjustment. You to remove the air cleaner when cold, lightly tap the gas and observe the air space in the Carb. throat, if almost closed loosen the three choke cover screws and turn the choke cover toward "Lean" to open it a bit more and try it then, and the next morning.

Also you can free-up a sticking choke by spraying the choke butterfly shaft and linkage with choke/heat riser cleaner, WD40 or other light lubricant.

StudeRich

[warrlaw1]

We always used to carry a screw driver to prop open a sticking choke to get a flooded engine running. Not much help on a Stromberg that opens to the rear, though. Had one of those backfire and start a little blaze. We also used to carry an old blanket to put out engine fires (lol).