uneven spark plug burn condition

[diben]

Hi, this is my first time posting.  I have a 1952 Canadian Dodge Regent 4 door sedan with a 218 ci flathead 6.  The engine has been rebuilt in 2008 and has 6000 miles on it since the rebuilt.  It has a pertronix in the distributer and it is a 12v negative ground.  All cylinders have compression readings at 150 psi. I have been struggling a bit to set the timing as the engine idles rough at start up but after warm up it idles a bit smoother but not much better.  I have set the initial timing at TDC idling at about 750 rpm any lower it shakes alot.  I have the original Carter BB carburetor that has been rebuilt several times over the years.  I have noticed that spark plugs in cylinder 1 and 2 are dry sooty indicating it is burning rich but the rest of the spark plugs for the other 4 cylinders are very clean indicating a lean condition.  Does anyone know why this might be happening?

[Sam Buchanan]

28 minutes ago, diben said:

Hi, this is my first time posting.  I have a 1952 Canadian Dodge Regent 4 door sedan with a 218 ci flathead 6.  The engine has been rebuilt in 2008 and has 6000 miles on it since the rebuilt.  It has a pertronix in the distributer and it is a 12v negative ground.  All cylinders have compression readings at 150 psi. I have been struggling a bit to set the timing as the engine idles rough at start up but after warm up it idles a bit smoother but not much better.  I have set the initial timing at TDC idling at about 750 rpm any lower it shakes alot.  I have the original Carter BB carburetor that has been rebuilt several times over the years.  I have noticed that spark plugs in cylinder 1 and 2 are dry sooty indicating it is burning rich but the rest of the spark plugs for the other 4 cylinders are very clean indicating a lean condition.  Does anyone know why this might be happening?

 

Welcome to the community!

 

Remote diagnostics is fraught with peril but a couple of things come to mind when reading your post. One, try setting your timing to 10*BTDC at idle. I suspect you will have a smoother idle and our modern fuels should handle the advanced timing just fine. You may then be able to obtain a lower smooth idle speed. Second, perhaps you have an intake gasket leak that is making some cylinders run leaner than others which could also result in difficulties getting a smooth idle. Try advancing timing, setting idle speed down and adjusting the idle mixture screw to see if this helps.

[diben]

Thanks for the response. I will try the settings you suggested and see if it helps.

[diben]

Tried setting timing to 10*BTDC and reduced idle to 600 rpm then took it for a drive and got a lot of back firing and hesitation when accelerating. I set it the timing back to TDC and had idle speed to 700 rpm and it drove with good power and acceleration without any backfire. Seems to run best at this timing. It’s just the engine shakes a bit at idle , my vacuum gage shows a reading at 18 with a slight shakey needle.  It’s just not a smooth idling engine and the spark plugs shows inconsistent burning between plugs 1 , 2 and the other 4 plugs.

[Los_Control]

There is a trick I learned years ago.

Use a $1 bill over the tail pipe exit.

The idea is that a engine is a air pump, it should push the $1 bill straight out.

 

The only reason the bill would flap back & forth is if the valves are not seating. .... sucking air back up the tail pipe ..... should not happen.

 

Just a quick & dirty test to check your valves.

 

My engine has sat for many years .... it runs ok in the driveway ....

Because I'm married ... I do not have a $1 bill in my wallet .... I used a piece of notebook paper to try the test.

It flapped back & forth so fast it tore the paper in 1/2.

 

My valves are not seating ... will cause a rough idle and poor reading on plugs for those cylinders.

 

For me that is a future Fred problem I will fix. .... for now I get by running in the driveway.

 

A quick & dirty test to check your valves.

[chris 48 P15]

here are some pages from book for p-15

hope it helps 

[Sam Buchanan]

1 hour ago, diben said:

Tried setting timing to 10*BTDC and reduced idle to 600 rpm then took it for a drive and got a lot of back firing and hesitation when accelerating. I set it the timing back to TDC and had idle speed to 700 rpm and it drove with good power and acceleration without any backfire. Seems to run best at this timing. It’s just the engine shakes a bit at idle , my vacuum gage shows a reading at 18 with a slight shakey needle.  It’s just not a smooth idling engine and the spark plugs shows inconsistent burning between plugs 1 , 2 and the other 4 plugs.

 

Sorry that didn't work, but at least you tried it. 

[vintage6t]

If the engine has sat for a long time, as mentioned above, you may have a stuck or sticky valve on those two cylinders. Try a little Marvels Mystery Oil in the crankcase and see if the rough running goes away after running it a bit.

 

The other thought is bad plug wires on those two cylinders causing weak or intermittent spark. I'd take a look at your cap and rotor as well.

[D35 Torpedo]

150 is very good. Try setting the idle mixture screw with a vacuum gauge. Check for vacuum leaks with non chlorinated brake clean. Just hose it around suspected areas when running and see if the idle changes. Check that your vacuum advance is holding vacuum. To check your plug wires just run it at night, and mist the wires with water. If you see arching they are no good. 

[diben]

Thanks for all the suggestions.  I did do the $1 bill on the tail pipe trick but being in Canada we don't have $1 or $2 bills so i used a notepad paper and the paper did get sucked back intermittently.  The engine does have a slight intermittent hesitation like a misfire when idling so it could be sticky valve issues.  I will check on plug lines, rotor, cap but they are relatively knew having been replaced last summer. I have been using a vacuum gage with my tuning the engine.  The adjusting the idle mixture screw doesn't seem to have much of an affect on the idle smoothness. It is currently at 1 1/4 turn out.

[Bryan G]

Has it been driven regularly for a while or has it been sitting a bit? My first thought is to go along with the notion of sticky valves. For that, I'd put a bottle of Marvel's in the crankcase and another in the gas tank, and then take a nice trip and try to loosen things up. Aside from that, I'd keep hunting for a vacuum leak.

[Sniper]

Best unsticker of stuck valves that I have found is brake fluid, use a precision oiler to get it on the stems.  You may have to pull the head to do that.  I use a plastic faced mallet to seat the valves and roll the engine over by hand to open them.  Doesn't take long.  Not sure if you can get to the valve stems thru the plug opening with the head on.

[D35 Torpedo]

Even compression indicates good valvetrain. Did you check for vacuum leaks? I run seafoam in my gas. I figure it's good "top end" lube.

[clarkede]

I had a stuck valve on one of my cylinders (see picture and notice second spring was not pushing valve back down).  I was able to free it with a screwdriver and a hammer and luckily there was nothing stuck in the valve seat area that might be impeading it from breaking free. At the time, my car had been sitting for about a decade and I really didn't want to pull the head off to inspect and I was sure it was something else.  Engine would run, but was running rough and I thought it was a tune-up problem.  Once I pulled the valve covers off and manually rotated the engine I could see one was sticking open.  I took a series of pictures as I manually rotated the engine because at first I didn't see any problem since the lifter was actually touching when I first looked.  However, as I rotated the engine I could see one was not moving like the others.  You might have one that is slightly binding or sticking.  You might be able to spray some lubricant up on the lower stems that might work its way up without pulling the head.  

 

Technically, it didn't take long to diagnose once I gave up on other issues like plugs, timing, carburator/fuel, etc.  I hope this picture helps to see what a sticking valve looks like.