[dataway]

What the scoop on the Hot Idle Compensator on a 704 Quadrajet? Do most people try to get them to function? Disable them?

This is a beautiful NOS carb, all the parts in the compensator looked like new, although I did destroy the gasket on the cover and don't have another one.

I vaguely remember disabling it in some way ... or maybe I was missing/lost/destroyed the little cork o-ring. Now that I read up on it a bit it seems I may have left it in a condition that would have it open all the time.

So, if disabling ... what is the best way to do it? Don't want to stuff it with epoxy since it's such a nice carb ... plug the air inlet stack with a cap? (I assume it's the pencil sized stack to the rear of the secondaries)

Engine ran great on the stand, idled very nicely ... but I did notice a pretty large lack of response from the idle screws, both out about 3/4 turn from closed ... not sure if a leaking idle compensator would do that or not.

[shaker455]

Block it off, use a soft plug
In some cases you can put all that stuff back into place.

[dataway]

The guts of the compensator are still in place ... just cap that stack with a rubber cap and be done with it?

[Kenth]

Cap the stack will do nothing to cure HIC vacuum leak.

You can replace the cork gasket with a proper sized rubber O-ring to seal the HIC.

Or, like Shaker455 said use a soft aluminium plug in hole to replace the HIC and put on the cover.

[dataway]

I noticed in the service manual diagnostics it says to plug the stack inlet to test the operation of the HIC ... if the HIC intake is plugged where is the vacuum leak coming from?

[Cliff R]

I don't leave the HIC operational on most builds we've done here.

A propane torch and an old wheel weight is used to some lead into the hole, then smash it out with a flat punch from both directions, problem solved and easily removed and put back to stock if needed. I always put the valve and cover back in place as well.

It really wasn't a bad idea and was standard equipment on a lot of carbs use thru the mid to late 1970's, then pretty much disappeared in the later carburetors.

The factory figured if you had your station wagon out on the Interstate and got stuck in stopped traffic on a hot summer day when it was 100 degrees outside, A/C running, etc, that the underhood temperatures could get hot enough to require a littl extra air to be added to the engine. This would increase idle speed a bit and help with cooling as the water pump and fan would speed up a bit.

Some say that it was done to lean out the carb at idle speed, One or both it is used to add air when things really get hot under the hood. The way these cars are typically used I see no need for it, and I've seen a good many of those valve leaking profusely as the spring in them had reach it's life expectancy...........Cliff

[dataway]

I checked the air flow diagram for the HIC ... I don't see any other inlet for a vacuum leak other than the stack ... manual recommends plugging it with a pencil for testing, or when sitting idle mixture on an engine hot enough to open the HIC.

So a rubber plug on that stack doesn't accomplish the same thing as plugging the orifice of the HIC ? Although I guess a good backfire might blow the cap off ... but engine shouldn't be bothered digesting a little rubber plug.

[Kenth]

Running the HIC w/o the gasket a vacuum leak occurs at the missing gasket, like the HIC never closes.
The stack provides fresh air from inside the air filter thru the HIC when HIC opens due to higher than normal engine temperature.
Setting the idle mixture screws requires to plug the stack with a pencil or rubber plug or whatever so additional air from HIC wont disturb the setting.
Some HIC covers has a plunger that needs to be pushed against the HIC valve too keep it closed when setting idle mixture screws.

The only way to permanently disable the HIC is to plug the hole with an aluminium plug where the valve sits and replace the cover so road dirt wont enter the engine thru the stack.

[dataway]

Looks like I'm going to have to find a gasket for the cover to start with before deciding how to plug things, not looking to necessarily .. permanently.. disable it.

[Kenth]

#71 is the gasket, #72 is the valve and #73 is the cover.
No gasket at the cover.

[dataway]

Jeez, coulda sworn there was a thin rubber gasket on my cover. But on reviewing my photos ... I don't see evidence of one. No wonder I couldn't find one.

I see now why people are plugging the hole ... if I cap the stack it will just pull air/debri by the unsealed cover. In normal operation that wouldn't happen because it would be way easier to pull air through the stack than past the cover.

Guess the carb comes off and it gets plugged

Thanks for the help.

[dataway]

Here is my solution to try first.

I cut a piece of neoprene rubber about 1/16" thick, reinstalled the valve which presses the rubber against the hole to seal it when you put the cover back on. The OEM arrangement uses this method to hold the valve against the cork seal. This should work the same way ... except no hole to allow the passage of air whether the valve is open or not.

Course this only works if you have the original valve.

[Old Goat 67]

Originally Posted by dataway

Here is my solution to try first.

I cut a piece of neoprene rubber about 1/16" thick, reinstalled the valve which presses the rubber against the hole to seal it when you put the cover back on. The OEM arrangement uses this method to hold the valve against the cork seal. This should work the same way ... except no hole to allow the passage of air whether the valve is open or not.

Course this only works if you have the original valve.

OR, a piece of wood and a pocket knife!

[dataway]

Or even a washer and a spring, actually just a wad of paper would work, even a hardened cat turd carved properly.