high speed flat spots

[djwlz]

I have a 1947 Lincoln and after it heats up it starts to get flat spots in the acceleration.  It has a new 6 volt electric fuel pump which has helped some.

I don't think at this point it could be fuel unless there is a collapsed fuel line, because it is fine when it is cold.  After the car heats up, the farther you

push the accelerator down, the flatter (lack of power) it is.  Could this be one of the coils going?

Thank you for reading this

Don

[19tom40]

It could be one or both coils going. Check your spark for a nice blue spark, 1/2" long at idle. Check from the plug wire to an engine ground. It could also be one of the condenser's staring to break down under load.

[djwlz]

Tom,

Thank you for responding.  I have checked all 12 sparks and they are working, though they weren't particularly blue.

Is there a simple test to figure out if it is one of the condensers?

Thx

Don

[ralphnof49]

The problem sounds like fuel shortage at higher speeds. Could it be a clogged fuel filter?

[19tom40]

If you have a good 1/2" spark to all 12 cylinders, the coil and condensers are OK. If the spark was orange or red, it is weak.

 

The best test for a condenser is to sub in a known good one.

 

Weak spark can be caused by weak coils, leaking condensers and incorrect point dwell.

 

Insufficient fuel delivery can be checked by pulling out the choke a little and seeing if that improves the condition. You could have a plugged fuel line from the tank or the flex line that is input to the fuel pump.

 

To check fuel delivery, you need a graduated 16 ounce or larger container to determine the amount of fuel delivered in a  measured time. Disconnect the fuel pump line from the carburetor and direct it into a graduated container. Crank the engine long enough to get 2 ounces of gas in the container and then continue cranking for 15 more strokes of the pump. The pump should have delivered 6 more ounces of gas.

 

Insufficient fuel delivery can be caused by a vacuum leak, plugged flex line, worn pivot in the pump arm, stretched diaphragm, plugged fuel  line or tank pickup, plugged tank vent or wrong gas cap or a worn push rod. The push rod should be 8 7/8" long for the cast iron manifolds and 7 7/8" for the aluminum manifolds. It travel is about 3/8".

 

The pushrod specs ore for a Ford, but the travel should be the same on a Lincoln Zephyr.

Edited April 26, 2016 by 19tom40
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[djwlz]

Thank you very much for all of the ideas, and suggestions.  I changed the condensers and the flat spot issue improved, but it still does it when it gets driven 20 miles, but less so.  I pulled all of the plugs and they all looked good and I re-gapped a couple of them, but only slightly so.  Now when I start it the idle causes the car to roll, and it acts as if it is going to stall.  What did I do to cause this, and how could it have a poor idle but be fine at higher rpms?  Next I guess I should try to replace the coil and see what that does.

Thx again

Don

[19tom40]

To fix your idle problem, try shorting out 1 plug at a time. The engine RPM should drop if the plug is firing correctly. You will not notice the miss at higher engine speeds as much as at idle.

[djwlz]

Tom,

Thank you, but how do I short out each plug wire without pulling it off of the spark plug itself?  I did this once already, but I read I can damage things by doing this.  Do you touch a screwdriver to the top part of the sparkplug where the wire is, to get it short out?

Thank you again

Don

[abelincoln]

After more than one shock, man that smarts, I took an old spark plug, connected high voltage plug wire to top, and clipped the base to ground.  Start engine, and observe spark from safe distance.  Also, if you have a clip-on timing light, you can see if each wire will make the timing light flash.

Abe

[19tom40]

I just use a screwdriver with a plastic handle, and touch the wire where it connects to the plug and a head nut. If you wish to pull the wire, use an insulated pliers or one of the plastic fuse pullers for the Buss type fuse. I pull the throttle out to run the engine at about 1,000 rpm, and watch the tach on my Tach / Dwell meter for a drop in RPM. Every cylinder should give about the same drop.

 

Abelincoln's timing light method, just shows that you have a spark at the plug. It does not let you know if the cylinder is pulling its load.

 

Pulling the wire off of the plugs in these older cars will not damage anything. Doing it on a modern computer controlled car could damage the circuitry.

[djwlz]

I have now replaced the coil, that has been tested as being good, and it made no difference in the rolling idle problem.  I tried the plug test again(grounding them), and they all seemed to cause a slight drop in the idle.  Problem is, there is still a roll at idle.  After having checked the plugs and gapped them just to make sure(about a month ago), I was surprised to find the plugs are now carboned up (black soot.)  This spark plug situation seems to have started with the rolling idle problem.  I tried the trick of spraying around the plugs and the wires with water in a dark garage, and that produced nothing.  What would cause the spark plugs to know be covered in black carbon?  Does this mean there is an issue with one of the new condensers, or is this an issue with the plastic terminal plates?  Thank you again for all of the suggestions.

Don

[19tom40]

Black carbon on the plugs, is usually caused by excess fuel, but it can also be caused by excess idling. The rolling idle problem could be due to the carbon fouled plugs or the carburetor leaking fuel.

 

You can check the carburetor for leaking fuel, by making sure the bowl is full of fuel, let it set overnight and check to see that it still has enough fuel. If it is leaking, have it rebuilt by Daytona or by .Charlie Schwendler 716 662 9159.....cas5845@yahoo.com .

[djwlz]

Tom,

Thank you again for all of the advice.  I just got back from somewhat of a speed run trying to "blow the carbon out" for about ten freeway miles.  It helped, but it didn't go away completely (rolling idle.)  I pulled a plug, once the car was back in the garage, and it was still black from carbon.  Is there a point where a plug cleaner is needed?  Or should I just replace the plugs?

On another topic, it has always had a low speed buck when the foot is off of the accelerator, either going down hill or coasting on the level in gear.  Very jerky, and I am sure the cars did not do this when they were new.  Of course this goes away when the clutch gets pushed in because the engine is being separated from the drivetrain.

Any ideas?

Again thank you very much for all of your assistance.

Don

[19tom40]

Don, I have not had much success with cleaning spark plugs. They seem to fail soon after they have been sandblasted. I would try a new set of plugs gapped with a wire gauge. You might try a hotter plug also.

 

The bucking that you feel is probably due to the idle speed set higher than the 450 rpm called for.

[djwlz]

On a 1947 Lincoln V-12 and a miss, and a flat spot at higher rpm, I am beginning to wonder if it isn't the distributor, which is of course a nightmare on these cars.  

A mechanic told me that timing checks now have to be done on older cars by driving them.  This is because of the burn rate of the ethanol (10%) in the fuel.  It said often times the timing has to be set more advanced than the original factory settings.  Does anyone have any experience on this?  Can the timing be changed without taking off the distributor, and taking it someone who has the special machine?

Thank you

Don

[Mssr. Bwatoe]

rolling idle and carbon plugs, with steady fire on all plugs is carb- distibutor is not tricky or problematic, actually the Holley built device is one of better units ever produced

and very dependable...get another carb, chk vacuum leaks..What is vac reading, and is needle steady?

 

[carbking]

I have not noticed a post stating the position of the idle mixture control screws in the carburetor.

 

Would suggest you at least try the following:

 

(1) Gently turn the each screw clockwise (in) until it bottoms, counting the exact number of turns (you can then return to this setting if the adjustment does not help).

(2) Now turn each screw counterclockwise (out) 3/4 of a turn.

(3) Start the engine and run at a fast idle.

(4) Once the engine is at running temperature, adjust the idle RPM using the throttle positioner screw.

 

3/4 turn may not be quite enough, but I would not exceed one turn unless the engine is totally worn out and burning more oil than fuel.

 

Theory:

 

The idle screws in this carburetor are of the "short taper" variety. As a general rule, the short taper screws have an adjustment range of from 0 to 1 1/4 turns.

 

In 1968, smog emission control became the law of the land. Due to more stringent idle requirements, most idle mixture screws were changed to a "long taper". The smaller delta when turning the screw allowed for much more precise idle control, thus emissions. The general range for the long taper screws is about 1 turn to 3 1/2 turns. Folks have have been accustomed to adjusting the newer carburetors get the older carburetors too rich; thus the rolling idle and fouled plugs.

 

Generally, rich running is ignition, which you have been addressing; however, sometimes there are multiple issues.

 

Jon.

[djwlz]

Jon,

Thank you for your response.  Today I took the car to a small local car show and then came home and tried to check the the spark plug wires while the car was running.  My first problem is I don't have a real pair of spark plug wire pliers, and I kept zapping myself.  I then tried starting the car and just checking three of them, after I loosened them , but then the car was very difficult to restart.  I finally gave up because I was running the starter so much, because it would not restart easily.  I did find the one of the spark plug wires on the drivers side, was up against the oil bath air cleaner---would that be a problem?   Anyway, I also added a quart of oil because it indicated it need it.  I backed it out into the street, and suddenly it kept trying to quit, and smoke started coming out from under the hood (scary).  I think it was oil blowing out from somewhere, but couldn't figure out what happened.  The car  then proceeded to go up a hill without a miss.  Are those float type of oil indicators accurate, or can they become logged like a fuel float in a gas tank can?

Thank you

Jim

[djwlz]

I have another question in regard to spark plugs.  It currently has Champion RH10C in it.  They were black with carbon, but now they are a dark brown.  Don't know if I should change them or not.  I have a 1953 Motors, and it lists the type of plug as CH-H10, and I have no idea what the difference might be.  If I go to a hotter plug, what is the recommendation.

Thx