McCulloch electrical problem.

Help Support ArboristSite:

Den

ArboristSite Guru
Joined
Dec 17, 2015
Messages
980
Location
Indiana
I sold my entire McCulloch collection... but just the other day, came upon an extremely clean Pro Mac 555. Price was right so I bought it.
The saw is in fantastic condition, magnificent compression, very nice paint. The saws fasteners, shields, and grommets all appear as though they have never been touched since it left the factory. The problem is, it just won't fire.

I pulled the plug boot and checked the spark with two different in-line spark testers. It sparks consistently and crisply. I've cut wood with chainsaws that had this amount of spark... so I figured it had strong enough spark. But now I'm not sure.

When I put a spark plug in the in-line tester, there is no spark across the electrode. I then tried this with five different spark plugs, with no success. Whether I hold the plug against the head for positive contact, or hold it out in the air, still no spark.

If I take away the in-line tester and put a spark plug directly in the boot coming from the saws coil,, still no spark across the electrode whatever I do.
Yet when I put the in-line tester back in, it sparks consistently in the in-line tester, and presumably strong enough to at least jump across the spark plugs electrode... but still no spark across the plugs electrode.

Of course when I turn off the ignition switch, there is no spark in the in-line tester. Then when I turn the switch back on, it sparks in the tester.

I have no more extra coils to try on this saw, since I've sold all the McCulloch's.
Question: Is a moderate and consistent spark in the in-line tester enough to jump across the electrode of the plug, or can normal impedence in the spark plug inhibit any chance of a spark at the plugs electrode in the event the coil is weak?


.


I
 
Old2stroke

Old2stroke

Never too many toys
Joined
Jan 24, 2016
Messages
1,076
Location
Ottawa, Canada
I have little faith in those testers, a simple valid test is to gap a plug to 0.080" and see if it will fire it in air with the plug grounded to the cylinder, if it does, it should also fire under compression. If the timing is way off because of a sheared flywheel key, verify that the FW magnets line up with the coil pole ends when the piston is coming up to DTC on compression. If not you may have to pull the FW and check. How are you trying to get it to fire? Squirting fuel in the carb or the plug hole I hope?

Oops, I missed the part where it wouldn't fire the plug by itself. Like stated above, if it doesn't do that you don''t have enough high voltage.
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
2,481
Location
Raleigh, NC
I sold my entire McCulloch collection... but just the other day, came upon an extremely clean Pro Mac 555. Price was right so I bought it.
The saw is in fantastic condition, magnificent compression, very nice paint. The saws fasteners, shields, and grommets all appear as though they have never been touched since it left the factory. The problem is, it just won't fire.

I pulled the plug boot and checked the spark with two different in-line spark testers. It sparks consistently and crisply. I've cut wood with chainsaws that had this amount of spark... so I figured it had strong enough spark. But now I'm not sure.

When I put a spark plug in the in-line tester, there is no spark across the electrode. I then tried this with five different spark plugs, with no success. Whether I hold the plug against the head for positive contact, or hold it out in the air, still no spark.

If I take away the in-line tester and put a spark plug directly in the boot coming from the saws coil,, still no spark across the electrode whatever I do.
Yet when I put the in-line tester back in, it sparks consistently in the in-line tester, and presumably strong enough to at least jump across the spark plugs electrode... but still no spark across the plugs electrode.

Of course when I turn off the ignition switch, there is no spark in the in-line tester. Then when I turn the switch back on, it sparks in the tester.

I have no more extra coils to try on this saw, since I've sold all the McCulloch's.
Question: Is a moderate and consistent spark in the in-line tester enough to jump across the electrode of the plug, or can normal impedence in the spark plug inhibit any chance of a spark at the plugs electrode in the event the coil is weak?
You can try measuring the secondary coil resistance to ground. It should be in the neighborhood of 5K ohms. If it reads infinite you have an open circuit in either the coil ground or high tension lead/connection.
 
  • Like
Reactions: Den

Den

ArboristSite Guru
Joined
Dec 17, 2015
Messages
980
Location
Indiana
Such a clean saw. Amazing compression. Nice paint.
I will probably sell the saw since I'm not interested in starting up another McCulloch collection.
The saw is so clean, I could not resist buying it in the first place!!! :)
You know how it is.

.
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
2,481
Location
Raleigh, NC
You can try measuring the secondary coil resistance to ground. It should be in the neighborhood of 5K ohms. If it reads infinite you have an open circuit in either the coil ground or high tension lead/connection.
After thinking about this some more I do think that you have an open circuit on the coil secondary either ground or HT lead. You have enough voltage to run the spark tester but since an actual spark plug has some leakage you need current to make it fire. Can't get current through an open circuit!
 
  • Like
Reactions: Den

Den

ArboristSite Guru
Joined
Dec 17, 2015
Messages
980
Location
Indiana
After thinking about this some more I do think that you have an open circuit on the coil secondary either ground or HT lead. You have enough voltage to run the spark tester but since an actual spark plug has some leakage you need current to make it fire. Can't get current through an open circuit!

SteveSr, How many ground locations are there to check... one? And where is it located?
HT lead is the plug wire from the coil up to and including the spark plug boot... right?
I despise these miserable electrical problems. My least favorite thing to fix !!!


.
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
2,481
Location
Raleigh, NC
SteveSr, How many ground locations are there to check... one? And where is it located?
HT lead is the plug wire from the coil up to and including the spark plug boot... right?
I despise these miserable electrical problems. My least favorite thing to fix !!!
I am not familiar with this saw model or its specific wiring. First thing to check is from the connector in the plug boot to the spark plug hole in the cylinder. You can try moving/tugging on the ignition lead to see if you have a loose connection in the lead. If it reads around 3-5K ohms that isn't the problem. If it reads near infinite/open circuit you'll need to start tracing the circuit to find the cause.
 
  • Like
Reactions: Den
Top