Low idle question
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
Low idle question
I have a 79 4speed. It always runs very smooth, most of the time idles at about 700 or 800 rpm. Today I was in stop and go traffic for an extended period of time with an out side air temp of almost 80 degrees and I noticed the idle wanted to drop to about 450 to 500 rpm and seemed like it wanted to stall. I then got it on the freeway for several miles and the next stop light I came to the car was idling just fine at about 800 rpm. Engine temp never got above 190 while stuck in traffic. Was it all that hot air swirling around the engine compartment while stuck in traffic causing the low idle? Just curious as to what the issue might have been.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
I suspect fuel boiling due to heat......as it happened in stop and go traffic......which is the real acid test.
There are several thing you can do to help the situation and/or check.
1) Where is your timing at and do you have the Vacuum Advance on full manifold vacuum?
2) Are you running the thick 1/4" Q-Jet gasket?
3) Is your heat riser verified to open at operating temp?
You can wrap the fuel line, which is easy but in some cases ugly. You can reseal the intake using a 1204 Fel Pro gasket which blocks the heat riser port from the head off completely.....this lowers intake temp pretty dramatically but you will have to convert to an electric choke. There is a GM heat sheild designed for Q-Jets but uncertain if it will fit as there is a lot of vacuum lines and other extra curricular items around that carb if stock.
Jebby
There are several thing you can do to help the situation and/or check.
1) Where is your timing at and do you have the Vacuum Advance on full manifold vacuum?
2) Are you running the thick 1/4" Q-Jet gasket?
3) Is your heat riser verified to open at operating temp?
You can wrap the fuel line, which is easy but in some cases ugly. You can reseal the intake using a 1204 Fel Pro gasket which blocks the heat riser port from the head off completely.....this lowers intake temp pretty dramatically but you will have to convert to an electric choke. There is a GM heat sheild designed for Q-Jets but uncertain if it will fit as there is a lot of vacuum lines and other extra curricular items around that carb if stock.
Jebby
