View original topic: Idle Shut-Off Valve
houseofboyd Tue Oct 18, 2016 7:27 am

I see articles on forums written up all the time about this little device and the issues it may cause. Iíve never had trouble with one (except for the other day), so I thought Iíd write up the symptoms that I experienced with a failing Idle Shut-Off Valve in hope that others may know what to look for if it happens to them. So this past Sunday, I decided to get Mabel out for a drive. It was a nice, warm fall day about 80 degrees outside. I drove her a couple of miles to a gas station, got a few dollars worth of gas, then headed down the road. About a mile away from the gas station, I had to stop at a red light. When I did, the motor died. It fired back up, but would not idle. I had to keep pumping the gas pedal to keep it running. I carried on to my destination, about another 3 miles away to visit my mother. After the visit, the engine was almost completely cool and fired right up but still wouldnít idle. So I had to do the whole drive with one foot on the brake and gas all the way home. By the time I got home, the engine was good and hot, I opened the deck lid only to hear a percolating sound from the carb and the base of the carb was very, very cold to the touch. Almost freezing cold. Based on articles Iíd read in the past, my first thought was the idle shut-off valve. Since it was so easy to get too, I removed it from the carb to test it with 12 volts. It appeared to work as it should when power was supplied. I checked the connectors from the valve to the coil just to make sure they werenít corroded, the looked fine, but I cleaned the terminals anyhow. Put everything back together, fired right up and idled perfectly. I let it sit for a couple of hours, then took it for a test drive around town, again, no problem, she idled perfectly every time I stopped. So, the conclusion is that I either have a failing shut-off valve or I had a bad electrical connection. For now, she continues to run great and idle great. The shut-off valve is a pretty cheap item, 15 to 20 dollars. I may order a spare to have on hand in case this one decides to fail again. Iím leaning towards a bad electrical connection though.

Chochobeef Tue Oct 18, 2016 8:05 am

Sounds like you just had a bad connection. Since its a plunger type device, it either works or doesn't.

Your carb icing would be more worrisome. Sounds like your intake heat manifold tubes are clogged with carbon build up and need to be cleaned out. Many threads about it here.

houseofboyd Tue Oct 18, 2016 8:45 am

Chochobeef wrote: Sounds like you just had a bad connection. Since its a plunger type device, it either works or doesn't.

Your carb icing would be more worrisome. Sounds like your intake heat manifold tubes are clogged with carbon build up and need to be cleaned out. Many threads about it here.

I'm going to look at that closer, the intake manifold is brand new (1300 miles) so I'd hate to think it'd be clogged already... :)

ashman40 Tue Oct 18, 2016 10:21 am

The cut-off solenoid (when OFF) blocks the flow to the bypass output, basically preventing the majority of the flow of air-fuel at idle. You could have had a bit of dirt/dust in the passage that cleared when you removed it.

You should also check/clean/flush the pilot jet on the right side of the carb. This jet feeds the idle circuit. Dirt in this can cause idle problems too.

On the issue of having a cold intake below the carb... this sounds like a problem with the heat risers that come from the #2 / #4 exhaust ports and pass along the underside of the intake manifold. They are designed to specifically prevent the intake from getting too cold; resulting in fuel condensing and pooling in the intake. This could also contribute to your symptoms. At higher rpms the high speed air-fuel flowing thru the intake reduces the temp of the intake tube. This causes fuel to form into liquid drops. When the rpms lower (coming to a stop) this pooled fuel will cause the engine to run rich and die. This only happens after the engine is warmed up. If you let the engine sit long enough the intake will "warm up" and the problem goes away until you get the rpms up.
Check that the heat riser tubes are not blocked. Feel the temp of the tubes on both the left and right sides. If one side is cool and the other is not, or the center under the carb is ice cold the tube is likely plugged or not working. Old intakes typically build up carbon in the tubes to the point where hot exhaust gasses no longer pass thru them. If you are running an aftermarket exhaust, does it have flanges for the heat risers and are they drilled open? Many of the cheaper aftermarket exhausts have you drill holes in the exhaust tube to allow gases to flow. This is less than ideal as there should be a defined direction of flow from one exhaust pipe to the other. Holes in the exhaust pipe mean the exhaust gases pulse back and forth without actually flowing. For the heat riser to work properly typically requires a venturi tube in the exhaust pipe with an exit pointing in the direction of exhaust gas flow. This draws (pulls) the exhaust gases thru the heart riser tubes, keeping the intake hot so fuel doesn't condense.

Chochobeef Tue Oct 18, 2016 10:22 am

Hrm. New manifold you say? When you go to check it, see if you can pass a hard wire from one tube out the other. It should have flow of the hot exhaust gasses which helps alleviate the carb icing.

houseofboyd Tue Oct 18, 2016 10:53 am

Roger that... Thank you both for your input... I'll let you know how it goes. :)

houseofboyd Wed Oct 26, 2016 6:33 pm

As I mentioned in a previous post, I ran into some trouble with Mabel. First thought it may have been the idle shut off valve and that still couldíve been part of the problem due to a loose connection, but it had nothing to do with the issue of the carb freezing and the car not idling after the motor was hot. Cold, the car would start right up, run fine for about 10 minutes or until hot, then it would not idle at all. I could hear a percolating sound coming from the carb and the base of the carb was freezing cold. That made me take a long look at the intake. Though the intake looks fine (fresh coat of paint when I bought it), it does appear to be the original intake and it is possible that the intake tubes are clogged with carbon. So, I decided to go ahead and order a new intake from And while Iím at it, I thought Iíd go ahead and order some new points, rotor, condenser and distributor cap from As I began to dismantle the top end to replace the intake, I pulled the distributor, removed the cap and rotor button and proceeded to put the points. Thatís when things when down hill. Unlike newer distributors and models, these points slid down on a shaft that was part of the VAC plate. Long story short, the shaft that the points sit on, pulled out of the plate. Hey, itís almost 50 years old, but still a bummer. So the search began for a replacement distributor. Luckily, I found the same exact distributor on a forum and had it in hand in just a couple of days. So all the new distro gadgets that I ordered from, went on that distributor. Iím going to sell my original distributor, somebody with the know how can rebuild it or use it for parts. The intake I ordered from CIP1 shipped with that God awful metal protecting black paint. I spent a good 3 hours stripping it down and painting it with gray engine paint. Looks so much better. So thatís where Iím at currently. I still need to strip down enough of the top end to remove the intake which is just sitting on the motor, bolts have already been removed. Once thatís done, Iím go ahead and put in new plugs and wires and adjust the valves while Iím at it. Hope to get a lot done Friday after work. I plan on keeping the original intake, cleaning it out and eventually using it again.

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