idle issue

[TCap]

Hi, I'm new to the forum. A little info on me and my ford; I have a 1930 ford model A deluxe coupe. She has been in the family since the mid '70's. My father did the restoration in the late 70's early 80's.

The car has sat for a while before I really had the time to work on her. I have had issues with backfires while going down hill with my foot off the gas and dieing at stoplights. I had the carb rebuilt, changed the points, new upper and lower distributor plates, new rotor, new plugs, new coil. Re-timed the ignition. Checked for vacuum leaks at the manifolds. She starts up easy but dies fast. Takes about three starts to keep her running. Once running she sounds fine at high idle but drop the idle speed and she doesn't sound strong and doesn't have "model A" sound. Sounds like she's missing. I checked plugs and noticed #1 and #4 are a nice tan/brown color, while #2 and #3 are clean like they have never been in the car. I'm still leaning toward vacuum leak...but why only two cylinders?

I'd appreciate your input and thoughts. Thank you.

[700rpm]

Have you done a compression check? You might have some kind of valve issue since it sat for a while. Are you opening the choke a full turn till it warms up, then turning closed to a good idle? Dying at stop lights usually means your carb float is set incorrectly or your main and cap jets are set wrong. "Rebuilt carburetor" can mean a lot of things, but not necessarily that it was set up correctly.

Welcome to the forum. Let us know what you learn.

[bogdonj]

I would start with doing a compression check to see if in fact you have a valve hanging up due to pro long sitting. If all that checks out I would suggest something wrong with the carb. I have had carbs rebuilt by a professional and still have acted up and had to fix it. Also do a quick check to see if the plug cap are set correct

[TCap]

I'll do a compression check and see what I get. What should the compression be? I only open the choke a half turn on cold starts, then set it at 1/4 open once warm. I was thinking of checking the float. Had a lot of fuel come out the back of the carb on start, but was fine after.

Thanks for the info, I'll keep you posted.

[700rpm]

Originally Posted by TCap

I'll do a compression check and see what I get. What should the compression be? I only open the choke a half turn on cold starts, then set it at 1/4 open once warm. I was thinking of checking the float. Had a lot of fuel come out the back of the carb on start, but was fine after.

Thanks for the info, I'll keep you posted.

Compression should be about 55-60 pounds, even all the way across. If you don't have a compression gauge, use your thumb; you can at least get an idea if the pressure is even.

When starting, turn the choke one full turn and only hold it open for about one turn of the engine, two max. Otherwise you'll flood it, which will cause gas to pour out the back of the carb. It should catch on about the second or third turn. Turn it down to 1/4 after about five minutes, unless you're at high altitudes or in very cold weather.

[Bob Johnson]

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What I find interesting is that plugs 2 & 3 are different than plugs 1 & 4. This means that something different is happening in cylinders 2 & 3 than in 1 & 4. You state that plugs 1 & 4 look normal and plugs 2 & 3 are clean. If the plugs have not been moved around and if they all have been in the car the same amount of time I would say that there is something going on in cylinders 2 & 3. It is unlikely that both cylinders 2 & 3 have independent similar problems. So I would guess that it is something that is common to cylinders 2 & 3. There is only one thing I can think of that is common to 2 & 3. That is the head gasket. My guess is that there is a break in the head gasket between 2 & 3. You could also have a coolant leak into 2 & 3 which would explain the clean plugs.

That is my guess
Bob

[Brentwood Bob]

What they said. Bob

[Dick M]

You could aso check the polarity of your coil. Be sure the positive (+) terminal of the coil is connected to the red wire and on the passenger side of the car. It will run if hooked up backwards, but it will not idle or run very well.

[TCap]

Ok, sorry this took so long. I did compression test. All cylinders show 58-60...except #2 which will not hold, nnedle just drops back down rather quickly.

[Bruce,Upstate NY]

Is your Vacuum wiper working OK?

[bogdonj]

There is your problem!take a flash light and look at the valves through the spark plug hole and see if the valves are closing and opening all the way while u manually turn over the engine by hand... Get a helper to turn the engine over while you do this and then let us know what you find

[Tom Wesenberg]

Originally Posted by TCap

Ok, sorry this took so long. I did compression test. All cylinders show 58-60...except #2 which will not hold, nnedle just drops back down rather quickly.

Did you bump the release valve on the guage?
IF the pressure came up, then it shouldn't drop off until the guage valve is pushed.

[Patrick L.]

Yep, it appears the engine compression is fine and there is/was a problem with the compression gauge while checking #2..
Did you check for a vacuum leak yet ?? I still use ether/starting fluid and just spray it along the manifolds while running..

[Aerocraft]

I would agree with Bob Johnson. The only thing shared by cylinders two and three is a very narrow section of head gasket between the cylinder walls. If there is a break there, the engine will still start and run, but not well. The plugs in those cylinders are "dry" for a reason. Gar Williams

[Mitch//pa]

if there is not a malfunction in the guage and indeed #2 cylinder has low compression then the next thing i would do is to perform a leak down check by pumping air into that cylinder.
also check to see if the air comes out of #3 hole. i am also thinking a blown gasket between 2&3 also combined with coolant getting into the cyl's cleaning the plugs

there are specific procedures to do a leak down ck

[TCap]

Originally Posted by Dick M

You could aso check the polarity of your coil. Be sure the positive (+) terminal of the coil is connected to the red wire and on the passenger side of the car. It will run if hooked up backwards, but it will not idle or run very well.

I checked and noticed the coil is hooked up with the red wire to the negative terminal and on the driver side. I had replaced the coil a while back and must have not paid attention. I will flip it around and see what happens.

[Tom Wesenberg]

The coil puts out the same high voltage wired either way, but the spark plugs take less voltage to fire when the hot center electrode is negative, and that's why CORRECT polarity helps to keep the plugs firing under extreme loads, like climbing a hill or flooring the throttle. CHICAGOLAND MG club has an excellent short read telling all about it. Just do a google search for "coil polarity", and it should be one of the first listings.

[TCap]

Checked valves in #2 by turning engine over by hand. Seems the valves are opening and closing fine. Switched coil wires, black to (-) and red to (+). Ran the car but still had issues with a miss and car would die. Ran car for 20 mins and then did another compression check. Got #2 to hold after a couple of tries. Showed around 50-55, still on the low end. 1, 3 & 4 all show 58-60. Guess I will try checking the manifolds for leaks again.