Heat riser valve thingie...

[jhellwig]

That little valve in the passenger side manafold.

Does it take vaccume to open or close? I have no vaccume line running to it right now.


My intake manafold is getting very hot very quickly under the carb and cooks the fuel out of the thing so that warm starts are very hard to do. It is an edelbrock intake and carb.

 

[Blue85]

Yes, it should be open except during warm up. I ditched mine when I went to headers, but I remember that it ties into a thermal ported vacuum source. It's really only an advantage if you are also using the THERMAC unit on the air cleaner. It gives you warm intake air during warm ups in cold weather.

If you can't get it to work right, just wire the thing open. You'll be wasting gas and losing power.

 

[btolenti]

The previous owner of my rig just tack welded the darn thing open.....haha!

 

[Leper]

IMO the heat riser is not your problem.

 

[NoReGrEtS]

IMO the heat riser is not your problem.

X2


I belive it take vacuum to close it
and not to open it.

 

[btolenti]

I disagree. A heat riser that is stuck in the closed position could definitely cause his problem.

That being said, I believe chevy designed them to fail in the open position.....but I am not really sure on that. It is possible that it is stuck closed, just not probable.

 

[Chevy305]

you might want to invest in acarb spacer that is not metal to keep the carb alittle cooler. search Jegs and Summit for one that will fit your carb/intake.

 

[diesel4me]

fail safe!..

Its hooked up so its only closed when vacuum is applied to it when its cold..there is an internal spring that holds it in the open position when no vacuum is present..so if its disconnected ,it will be open..

I found my 305 runs much better with the heat riser closed during my usual 5-10 mile runs to do errands in the winter's cold..it warms up faster,gets better MPG,and I swear the heater even works better!..when I'm planning on going on a longer trip,I remove and plug off the vacuum hose..
I've been too busy to hunt down another thermal vacuum switch (its the one in the t-stat housing that controls the EFE valve/heat riser)..but plan to soon..

My edelbrock is a cold blodded S.O.B. on cool damp days with rain..it will frost up and stall every time you try to idle it,and is dangerous in traffic!..I found leaving the EFE "closed" helps a great deal in that situation..I suppose everyone in CA and AZ is now wondering "WTF is a heat riser?"...

 

[jhellwig]

Cool. Thanks.

I was mostly checking just to make sure that I wasn't burning the crap out of something that I could have avoided buy just some cheap vaccume line.

 

[1-ton]

I suppose everyone in CA and AZ is now wondering "WTF is a heat riser?"..

Vehicles in the west coast come with EFE valves as well, but they are not needed unless you live up North. The California smog Nazi's actually inspect for EFE valves as part of there visual inspection. Hell, they even require you have the little dash pot, and 12 Volt activated vacuum solonoid, which kicks the carbureter throttle lever up higher, when you turn on your air conditioning.