Heat riser exhaust valve

[80c10305]

The heater riser valve on the outlet of the passenger side manifold, does that open if manifold vaccum is applied to it? I know it gets a vaccum source through a coolant vaccum switch, just verifying my understanding of that vaccum circuit.

 

[Ricko1966]

Vacuum closes it based on temperature to send exhaust through the intake manifold passage on cold days. That's one of the problems with vortec heads no heat crossover for cold weather.

 

[80c10305]

So vaccum closes it. Alright. I can’t see or find how that valve looks with the flapper open .

The reason I ask is, all the vaccum lines for all the emissions and such except vaccum advance was removed and I’ve been wondering if part of my rough idling could be partly caused by that

 

[Rusty Nail]

That vacuum line runs to the switch on top of the thermostat housing.
The other line on that thermostatic vacuum switch (TVS) controls the flapper on the air cleaner connected to the heat riser tube in certain models. Not likely to make your truck run bad but it will make it run rich sometimes? and probably costs fuel mileage under choke conditions.
Might wanna check the EGR operation.

 

[80c10305]

There is no egr anymore. The 4bbl intake I put on there has no egr provision.

I don’t mean to be a pain but to be clear, if I supply vaccum to ,that vaccum canister for that heat riser, it pulls the heat riser valve open?

 

[Goldie Driver]

There is no egr anymore. The 4bbl intake I put on there has no egr provision.

I don’t mean to be a pain but to be clear, if I supply vaccum to ,that vaccum canister for that heat riser, it pulls the heat riser valve open?

It pulls the heat riser valve closed. No vacuum it is defaulted by the spring to open.

So, exhaust passes thru the intake under the carb to help fully evaporate the liquid fuel to vapor, thus the Early Fuel Evaporation name. The exhaust is only able to get out the drivers side manifold when the valve is closed, so more back pressure for sure.

 

[80c10305]

10-4. Thank you for the clarification. I’ll just leave it unhooked then. Thank you!!!!