1972 Evinrude 65 hp weak spark - FIXED!

[jeftfm]

Hi all - hope you can help me. My 1972 Evinrude 65hp (65272) won't start and I think it's a spark problem.
* No apparent spark on any plugs when holding them against the engine block
* When I hold a screwdriver into the HT boot and place it near the block, the spark jumps at about 5mm (1/4 inch) and looks very weak
* Brown wires (4 and 5) to the stator show around 78V AC when cranking the starter. (Bear in mind the battery is a bit low so cranking wasn't at full power). Thought this was meant to be about 300V
* Have tried disconnecting the key switch ground wire (#6) but no change
* Had a flat battery just before this trouble. When I got it going on a jump start, there was only a marginal voltage increase across the existing battery (0.5V) with the jumper leads removed so I suspect a bad rectifier.

Can't help feeling the low spark and no battery charging things are related and seem to point to stator or power pack? I'm trying to pinpoint what part is faulty as I'd prefer to only replace the bit that needs fixing, (ie don't want to spend lots of money!)

Any thoughts?

 

[racerone]

Re: 1972 Evinrude 65 hp weak spark

Re: 1972 Evinrude 65 hp weak spark

The motor must crank fast at over 250 RPM in order for the electronic magneto to work.---First step is to try a known good battery and to inspect the starter motor.----------The battery is only used to crank it over.---The magneto produces the spark.

 

[boobie]

Re: 1972 Evinrude 65 hp weak spark

Re: 1972 Evinrude 65 hp weak spark

The proper way to check out the ignition system on that motor is with a volt/ohm meter and a DVA adapter. And the correct specs.

 

[F_R]

Re: 1972 Evinrude 65 hp weak spark

Re: 1972 Evinrude 65 hp weak spark

Yes, a "regular" Voltmeter without the DVA adapter will give false readings.

Are your stator's charge coils oozing goo? That was a common problem, and if they are, it is toast.

 

[jeftfm]

Re: 1972 Evinrude 65 hp weak spark

Re: 1972 Evinrude 65 hp weak spark

Hi all - thanks so much for the suggestions - have fixed the problem, thought I'd let you know the solution.

Turns out it was the starter motor not driving the flywheel fast enough. I initially replaced the brushes but without success and then noticed the pinion gear (called the drive assembly on the parts chart) was slipping inside the housing so while it engaged the flywheel properly, it struggled to turn the flywheel over, giving the same symptoms as a bad battery. After replacing the battery and then driving it straight off the battery terminals, it still would only just turn over with plugs in (normal compression).

So replaced the pinion gear (and the brushes for good measure) and it spun the flywheel enough to deliver plenty of energy to the coils. Had already replaced the spark plugs and hey presto! the old girl burst into life with a nice bright spark.

Out of interest I tested the old plugs and the spark was bright but very yellow so the new plugs were necessary too.

So thanks for your suggestions - (esp racerone you were right about the starter).

I had it out today and it started great - it runs rough at low revs so guess the carbs need a check an clean but at least I can get to the fish again!

Cheers, Jeff