Engine misfiring on 2 cylinders

[star_sail]

I have a late model (1972) model Atomic 4 engine that I am having ignition problems with. In trying to track-down the culprit I have replaced the distributer cap, rotor, condenser, coil, spark plugs and wires. The engine seems to run pretty good although I think it could be slightly smoother and there is a little smoke in the exhaust. I have a spark tester that I can attach to the wires while the engine is running that indicates two of the cylinders are firing with a steady spark while the other two are mis-firing occasionaly. Of course this means that the spark plugs are getting fouled-up quickly and as the plugs get worse the engine performance gets worse.

Someone told me that the atomic 4 is known for having the distributer bushings wear which causes the shaft to move. I tried moving the shaft just under the cap and I was able to move it slightly (maybe 10 thous.).

I am somewhat at ropes end trying to diagnose this problem. I have never pulled a distributer out of an engine before and am concerned about the further expense of parts to (hopefully) fix this problem. Another option is to buy a new distributer with an electronic igninition, assuming it is a fairly "drop-in" replacement option other than the timing.

Any advice would be appreciated...

Thanks,

Lance Hillbrecht

[tenders]

You're using Marvel in the fuel? And your choke and mix are set properly? Sticking valves could also account for what you're seeing.

For a little over $100 you can have an electronic ignition and Moyer's slightly-hotter-than-stock plugs and I bet you'll be all set.

[Don Moyer]

Very interesting, but I'll be quite surprised if worn distributor bearings
turn out to be your culprit. Is there any disparity in the compression
between the good cylinders and the ones that appear to be misfiring?

Don

[star_sail]

Very interesting, but I'll be quite surprised if worn distributor bearings
turn out to be your culprit. Is there any disparity in the compression
between the good cylinders and the ones that appear to be misfiring?

Don

Thanks for the reply Don,

I tested the compression twice. While cold I got 110, 105, 110, 110 on 1 thru 4, and while hot 115 PSI on all cylinders. I have somewhat disregarded carburator or problems other than the ignition just because the tester I have clamps onto the spark plug wire and senses the voltage when the cylinder is firing. Even if it was the timing I would assume that all the cylinders would fire at a steady rate as they are all getting a regular spark, they would just be sparking at the wrong time. When clamping the tester on the wires I can see that two of the cylinders are often missing a regular spark. I have also checked and rechecked the points to make sure they are gapped properly (.018 - 0.20).

I replaced the coil and bought one with an internal resistor but don't think its faulty just because the spark seems to be regular on two of the cylinders. If it were a problem with the coil I would think that either it wouldn't work at all or the mis-firing would occur on all the cylinders rather than just a couple.

Lance Hillbrecht

[Don Moyer]

Lance,

Are you using Champion RJ12C plugs or equivalent, and have you tried moving
the plug leads to different cylinders to see if the trouble follows those
particular positions from the distributor? Not knowing which two cylinders
are defective, I don't know if the plug wires will be long enough or not.

Don

[star_sail]

Plugs...

Lance,

Are you using Champion RJ12C plugs or equivalent, and have you tried moving
the plug leads to different cylinders to see if the trouble follows those
particular positions from the distributor? Not knowing which two cylinders
are defective, I don't know if the plug wires will be long enough or not.

Don

I am currently using the normal recommended plugs (not near my manual but think they are the RJ6 plugs, but have read about the hotter plugs and have purchsed a set but have decided to wait putting them in until the brand new ones get fouled.

I have not tried swapping the wires just because I was concerned how badly the engine would run considering how badly the firing would be off (and possibly damage that may occur). Should I try it?

Thanks,

Lance

[baileyem]

Plug wire swap

Lance,
I think that Don was suggesting that you swap plug wires by swapping wire number one for wire number two, etc. by removing wire number one from both the plug and the distributor cap , doing the same with wire number two and then replacing wire number one with wire number two and wire number two with wire number one, in order to see if the problem travels with the wire.
I am sure that he was not suggesting that you simply change the wires on the plug end only.

Mike

[Don Moyer]

Lance,

In swapping wires, you need to retain the same firing order. This limits you to changing the wires that will reach from the particular post on the distributor cap to the appropriate plug.

Don