[i1lusion]

The passenger side exhaust manifold has a valve on the bottom section with a vacuum diaphram to open or close it. My first question is why is it there, what does it do? Is it to heat up the intake and then allow the choke to heat up? Second question is: is it opened or closed when there is no vacuum supplied? I would like to wire it open since I'm putting in a manual choke, but I dont know which way is open.

 

[macario]

Specify year, make, model of vehicle in question.

 

[oldmanram]

The passenger side exhaust manifold has a valve on the bottom section with a vacuum diaphram to open or close it. My first question is why is it there, what does it do? Is it to heat up the intake and then allow the choke to heat up? Second question is: is it opened or closed when there is no vacuum supplied? I would like to wire it open since I'm putting in a manual choke, but I dont know which way is open.

Vacuum controlled 'heat riser' (at least that's what I call it, Santak and I had a fair amount of confusion concerning the correct terms for this) I can't tell you about the vac. It does help warm up the engine, when cold it's closed, I would say check the vac with the engine either dead cold, or full op. temp. and see what the vac. is doing, or just drop your exhaust pipe off the header so you see what you are doing and wire it open !

 

[i1lusion]

Specify year, make, model of vehicle in question.

85RC 318 Auto 4X4 stock

 

[mattnsue]

Mine is an 84 318, should be open with no vacuum and, of course close with vacuum.

 

[macario]

I'd say wire it open except I know your winters can be cold there.

Mac

 

[oldmanram]

I'd say wire it open except I know your winters can be cold there.

Mac

If your changing to a manual choke, my guess is that you'll never miss it... I've never had a rig where one of these dang things worked, they're always broke, missing, or somehow wired open... just bad luck, I guess

 

[Smokey]

Yep, us ole coots call it a heat riser, and it's function is to close when cold.

When closed, it forces the hot exhaust up through the little center port on the intake side of the head, across under the carb to heat the intake manifold for better fuel vaporization in cold weather. Then that portion of the exhaust flows out into the drivers side exhaust.

Block it open, unless you have severe cold weather driveability problems. The passage up and over is probably carboned up solid anyways,,, most are in high mileage vehicles.