HELP! Rebuilt engne less than 700 miles. Engine started acting irregular, low vacuum reading, sooty spark plugs. Will no longer idle correctly.

[Torisco]

Similar to what I have. Stay away from the ones that you need to hold on place.

View attachment 947902

Got it off Amazon years ago.

Amazon.com

Thank you.

 

[Torisco]

Won the compression tester I bid on, with a ridiculously low bid, before being offered one by Ziggy 0. Sure appreciated the offer but was stuck with the bid I previously made for a tester.

Got my coil from Da Bella and got my distributor points rotor and condenser. Tester will arrive next week and I will again try to fix my engine problem and report what happens next week.

 

[Torisco]

Had a family emergency and had to step away from my M43 problem. Am now back at it and family issue came out fine.

I tested the compression 1= 100, 2 =95, 3=97, 4=95, 5=98, 6=100.
I think compression is not a problem.

I pulled number one plug to check for spark. Grounded the plug body to the engine and cranked it over. I got a yellow spark (not a sharp blue spark) that seemed weak to me? Could the coil, points or condenser be the problem and fail after warming up? I have bought new replacement coil, points and condenser and think I will be changing them out.

The problem I have had from the start is a follows.

Starts up O.K.
Left to idle and warm up the engine will eventually slow up and die after warming up. It then will not restart unless you let it sit for quite a while.
The plugs all show black soot as though the fuel is not being completely burned. Replaced all plugs new. Rebuilt carburetor, checked for correct timing (it is within a degree or two).
Checked compression and all are within range.
Checked idle adjustment setting and fuel mixture setting. Gauged the carburetor float to spec when rebuilding carb. Idle screw was set at 3/4 turn from closed
Vacuum is around 17 - 18 (air filter and carburetor horn removed. Air lines to distributor from carburetor horn are disconnected)
Throttle advance or revving after initial start up responds as it should until the engine warms up and dies.

Does anyone have any ideas as to what could be causing this?

 

[John Mc]

I hope you are not running the engine for long with the vent lines to the distributor disconnected.

 

[Torisco]

I hope you are not running the engine for long with the vent lines to the distributor disconnected.

Thank you for the info I had no idea about.

A Test run goes probably around 5-10 minutes max. at idle before the engine quits. The two air horn lines are connected at the distributor but the air cleaner and air horn assembly are and were off when I have test run the engine.

I read somewhere that if there is no air circulation to the distributor that the distributor cap trapped air area would become electrically charged causing misfires. Can you educate me on whether I should only test with the air lines to the horn and the horn itself connected. And would this lack of air circulation to the distributor lines cause my problems by that issue alone?

 

[John Mc]

I have no idea how long it takes for things in the distributor to build up to problem levels. I'll have to leave the actual education to someone who knows what they are talking about. A lot of people claim the vent lines are for cooling. However, a couple of very knowledgeable people have told me they are really to flush out the ionized air that builds up. If I recall correctly, it can cause misfires due to arcing and can also cause damage to the coil.

Take that with a grain of salt, however. I'm just repeating what I had heard.

I know when we swapped out the original carb on my 251 for a Weber 2 barrel carb, we had to come up with a new way to get flow through the vent lines. It doesn't take a lot of flow. I had thought about using the bubbler pump from an aquarium, but wasn't sure how well that would hold up to installation in the engine compartment.

 

[JimC2]

If you have a primer installed, check it for leaks.

 

[Torisco]

I greatly appreciate what you have told me. After rebuilding the carburetor I have been running and testing the problem for, at least, half a dozen times for 5- 10 minutes without the air lines connected to anything (just hanging there). The original problem that started all of this appeared to be carburetor malfunction of over abundant fuel to the engine. I had gone 600-700 miles following all break in procedures since rebuild before this started with no problems. I did change the points in the distributor and was off by about 2-3 degrees on the timing since the rebuild and start of the problem. with all of this in mind...what would you make of me seeing a lack luster yellow spark from the number one piston spark plug versus the snappy blue spark I think I should be getting? And I do detect an intermittent miss when I am able to run the engine.

I will proceed to change the coil and replace the points and capacitor, set the timing to 2 degrees before TDC (approximate within 2 degrees) for number one piston, reinstall the carburetor horn and reconnect the distributor air lines. Only then will I try a test running of the engine again.

What do you think of this approach? and I will post the results on or before the 14th as I only have sunday to work on the old gal. Thanks again for assisting. It truly helps a lot.

 

[Torisco]

If you have a primer installed, check it for leaks.

I do not have the primer installed on this rig. Thank you for the input.