g741.org

Hi all:
You guys have helped me many times in the past 15 years with M37 issues.
I need help with an electrical problem.
Here’s the facts: Vehicle is an M715 in excellent condition
New plugs, new electronic ignition, new rotor,
new cap. Fresh gas from a remote gas container. Compression is good on all cylinders.

Has run for very short periods of time, but not often, like 5 minutes then dies. Also same symptoms
before electronic ignition was installed. Will not restart using starting fluid or gasoline directly
down the carb throat.

Testing the spark on #1 wire hooked to the plug, spark is sometimes good, sometimes weak,
and sometimes not at all. Intermittent would be a good description. Same symptoms with
points and condenser or electronic ignition.

Would you guys please suggest more ideas to remedy the problem.
I realize this is an M37 site, not M715 but the electrical systems should
be the same. HELP !
Jerry Bubolz

You didn't mention anything about testing or replacing the coil? Could be it fails once it warms up.

Or a bad connection somewhere in the primary circuit.

I agree with a weak coil or connection problem.

However I will share this
My M37 runs perfect. Has for many years.

One time it developed symptoms close to yours.
I thought fuel or vapor lock, but ended up being the Charging
System over charging (high voltage) and over heating the coil.

I noticed the volt meter had creped out of the Green into the Red.
30.+ volts according to my VOM
Replaced Voltage regulator after trying to adjust with no luck.
Truck now show's 26.5 to 27.5 sometimes 28 volts but never more.

No running problem from ign. since.

Tom

Elwood and Tom P.

Thanks for the ideas. I have suspected the coil. Gets hot, maybe, and quits.
How can coil be tested? They are expensive to buy for trial and error.

I will also check the charging system for excessive voltage.

Thanks,

More info to follow after further testing.

Jerry

Here is a recent topic about ignition problems and testing coils: http://www.g741.org/PHPBB/viewtopic.php ... oil#p71052, and there are many more through the search function. These will cover some of the basic coil tests using an ohm meter, but probably won't be conclusive if the problem is heat and/or time related.

As to testers, Sun Electric used to make portable military coil testers for 24v systems, such as the AAM5.864 and the CCT-20. These can still be found on eBay from time to time. I picked up a CCT-20 not long ago, but have not had time to test it. Sun also made a cabinet-style engine analyzer for the military that could test almost everything on a 24v vehicle, but these are much harder to find.

These electrical systems are getting old enough that a spare coil is becoming a part of the OVM, in addition to points and condensor, plugs, etc.

Jerry, is this the 715 in Payson?
Give me a call I have some things for you to check.

Elwood: Thanks for the info on coil testing. I’ll check it out.

Greg: I’m now in Apache Junction.
Thanks for the telephone call and the advice on the distributor.

Jerry Bubolz
AMVCC. Phoenix

I had a similar issue on my M37 with the flat head 230.
I have the chrome Chinese coil. The dimensions of these coils are slightly different than the original US made coils.
Most of the Chinese coils are not as long as the US coils and may not bottom out into the distributor housing properly for heat transfer.
This can lead to over heating of the coil.
I cut a piece of .030" thick copper into a circle that fit into the recess of the distributor where the coil drops into. See pic.
My process:
1) Cut the .030" copper sheet into a circle that will drop into the recess of the distributor
2) Burnish the bottom of the chrome coil with green Scotch Brite.
3) Burnish both sides of the copper with the Green Scotch Brite.
4) Coat both sides of the copper circle insert with thermal paste.
this is the same paste used on computer cpu's and other electronic components.
5) Insert the coated copper circle into the distributor housing making sure it seats into round recess.
6) Insert the coil into the distributor and secure with the two screws.
Hope this helps
Jerry, if you are in A.J. now, lets meet up sometime for coffee at Hackers or Handlebar
Also, if you are in need of some under carriage work on the M37, I have a 4 post lift. Give me a shout at the next AMVCC meeting.
Mike

Sorry for the late reply. I’ve been running around like a cat covering poop.

Thanks for the copper tip Mike.
Text me when you want to meet up.
480-227-8876
Jerry