1981 120 Mercruiser idles rough when hot

[Dannysmyk]

Okay so update all.
i got a fuel pressure test kit but it did not have the right fittings so i could not test that. I have very low suspicion that is the issue anyways.
Compression
cylinder 1 130
cylinder 2 105
cylinder 3 140
cylinder 4 130
Removed the distributor cap and shaft has little to no play removed and tightened the screws to the spring mechanism under the rotor cleaned it up all nice and put it back together.

Went after it again today... two pumps. a flick of the key and boom running great.

ran for 20 min and didnt want to idle again

Funny you guys mention the electronic igntion its a peritronc with the peritronx coil 3 ohm coil (ballast resistor in it). I jumped the old inline resistor by runing a new wire from the coil to the ignition when it was installed 2 years ago.

Today i noticed something when it started messing up. The coil was HOT real HOT my finger is kinda burnt from touching it. Is this normal? Cant be. Ive heard of coils getting hot and causing issues. What would cause that? bad coil?

 

[Dannysmyk]

Most aftermarket electronic ignition upgrade components work quite well out of the box however I've seen a few fail within a week or two of install. I've seen some behave exactly as you describe, work great first 20-30 mins but when fully warm/up to temp they start to fail. Would be high on my list of suspect components in your situation

When the engine starts to exhibit the issue check the idle timing, of its okay check the spark quality

When it starts to stuble timing is irradic jumping all over

 

[Scott Danforth]

FWIW, every pertronix kit I used failed. That is 3 out of 3 on 3 different motors. Always went back to points

 

[flashback]

Not uncommon for a coil to get hot, but if it burned you then too hot. May have a short in it. What Scott said is the reason I decided not to go that direction.

 

[dubs283]

Coil getting hot could be a failing sensor assy, especially seeing the erratic timing jump when the engine runs poorly

I've had similar experiences others have posted about with pertronix. They work for a while, then they don't. Avg. failures I've seen is about five seasons

 

[Dannysmyk]

Success at last.
When i felt how hot the coil was i ran to the autoparts to get a new "stock" coil, reconnected the ballast resistor, and it ran good for over 20 minuets!
Like they say shes fixed for now we will see what happens when i put it in the water this weekend.

Thanks for all the help

 

[ROY WILLIAMS]

Success at last.
When i felt how hot the coil was i ran to the autoparts to get a new "stock" coil, reconnected the ballast resistor, and it ran good for over 20 minuets!
Like they say shes fixed for now we will see what happens when i put it in the water this weekend.

Thanks for all the help

yes that ignition coil very hot off the resistor damaged it ... new ignition coil ..