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1975 Johnson 3cyl loop charge 75hp 75ESLR75B Intermittent loss of power on accel

moparschmidty

moparschmidty

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1975 Johnson 3cyl loop charge 75hp 75ESLR75B

intermittent no/reduced power on accel.

Intermittently will not accelerate but to maybe 30% of potential, at other times runs fantastic, (although when running correctly, it would seem to me, it should respond faster to rapid launch/throttle up. if it were a street engine I'd bet it was Holley bog)

Meaning as simple as shut down and restart and it's fine. Throttle cable back and forth, shifting reverse and back to forward no change. I find no binding in mechanicals under flywheel (advance) .

Adding fuel (false fuel enrichment, during reduced power) made no difference.

I did some measurements with both my Fluke 87 & 88 for minmax AC voltages, as I do not have the DVA (direct voltage adapter) adapter, and my readings were not close to what's shown in CDI Troubleshoot values. (stator and timer base, white/black and black/white wires).

Would (should) the Fluke Minmax readings (low, high, and average) be the same as the recorded DVA readings?

Seeing that this is an intermittent, and I'm not big on diagnostic darts being thrown, and it resolves with a key cycle (most times), I'm leaning towards the power pack (screw type) not switching over in timing advance. (lack of correct tool and knowledge/experience, may lead to SWAG diagnostics, Scientific Wild Ass Guess)

After a key cycle (or two) it runs okay. Is there such electronic ignition control in stator or timer base, to control timing advance, that could be affected by cycling the key? (switched ignition)

Work performed so far (and it's winter and working from memory of last season)
1 - I installed a bypass toggle switch in black with yellow (stop) wire, that made no difference.
Idles fine when this happens.
2 - Rectifier replaced, wire insulation (s) were burnt and it looked like it may have been grounding out.
3 - Carbs cleaned out
4 - Rubber hoses replaced
5 - Powers and grounds are good
 
First of all the powerpack does not " switch over in timing advance "-----Not sure where that wild idea came from.-----No electronic timing control in the stator or timer base either !!-----The timing advances simply by rotation of timer base.-----How did this motor run for you in the past seasons ?-----Did you clean the little brass jets ( 5/8" long ) found in the very bottom of the float bowls ?-----Nozzle gaskets in place ?----Does spark jump a gap of 3/8" or more on a test device ?----Flywheel key checked ?----Cycling the key should make no difference.------Run with a timing light one cylinder at a time to see if you are losing spark.
 
Basing my thought process on automotive ignition modules and timing control, with module controlled electronic spark timing. Believing a module could have problem based on "intermittent" no accell/no power no matter what I do with controls or adding false fuel (spraying carb spray into intake on throttle up) or changing throttle controls i.e. timing base. However, shutting engine off and restarting and it runs fine, throttles up and screams away.
I have a spark tester and set to 30kv setting it jumps that.
Looking for thoughts on intermittents. What would cause intermittents? Not losing specific cylinders. Since this is charging system controlled ignition.
 
I could rebuild that motor without a glance at a manual.----Your motor is a very simple one.----An electronic magneto.----Good luck with it.
 
Two things immediately come to mind simply because they are so common in those motors.

1. Water from exhaust cover getting into cylinders. Somebody has already suggested that, above.

2. Sticky timer base. The timer base is moved (advanced) by a spring in the vertical throttle lever. If the timer base sticks, the spring simply winds up without moving it, and the carb butterflies open. By design, the timing is supposed to fully advance before carbs open significantly. If the carbs open before full timing occurs, it will stumble and fall on its' face, maybe even stall. Is this what you describe as Holly bog?

Of course, neither of these are related to the key switch.
 
Thanks for the response, I'm not sure about vented prop. 16ft Tri Hull. I did put a different prop on for pulling skiers, and same intermittent. (this has been an ongoing problem since purchase) The guy that gave me the prop had knowledge of these engines and stated this was the correct prop for the stinger and both are built the same, different pitch for pulling skiers. What should I look for in vented or not vented? Should it be vented?

(Still in very cold climate up here top of the country, just trying to get a handle on forming proper diag, and not tossing parts on, although I would not mind a "good known parts department" aka properly running test engine)

About the Digital Voltage Adapter, will it function the same as my Fluke DVOM's for reading the voltages? I have tested the blk/white & white/black repeatedly between the module/power pack (last summer), timer base, and stator, and in those readings with the DVOM, recorded measurements are no where near, listed values using minmax. I had the tests all written down but other things can occupy the top of the tool chest over the months. I have done extensive diag, but can not verify readings without knowing proper values without the DVA, unless of course it is just an adapter to a regular DVOM that essentially would works as my Fluke meters recording capability of AC low, high, and average values. Like to rule out the need for the special tool.
Resistance values all good all circuits, the values on the cranking (AC voltages?) aren't close, with Fluke 87 & 88's.


5. Check the stator and timer base resistance and DVA output as given below:
WIRE READ TO OEM RESISTANCE CDI RESISTANCE DVA (Connected) DVA (Disconnected)
Brown Brown/Yellow 400-600 400-600 150-400 V 150-400 V (*)
Black/White White/Black (all) 10-20 30-40 0.6 V + 0.6 V + (#)
Black/White Engine GND Open Open 150-400 V (a) N/A
White/Black Engine GND Open Open 150-400 V (a) N/A
(*) This reading can be used to determine if a stator or pack has a problem. For instance, if you have1-red.jpg
 
Thanks.
That's key switch part is what gets me, when it's experiencing the reduced power symptom, I shut engine off and restart and it's fine.
Sounds like sticky timer base would be closest to my symptom, no advance intermittently. But the throttle down and into reverse, back to forward and throttle up does not change the condition. Possibly a bind created then is released on engine shut down and on engine shaking on start-up allows movement?
And I'm new at the blog stuff so if I'm failing at proper posting, apologies to all.

In response to earlier posts and this one I will check for water from exhaust cover (however, the intermittent thing gets me)
 
fdrgator,
yes, "Holley Bog", experimenting with different carb accel pump cams for fuel used, weather, axle ratio, track conditions timing etc. for best launch. Eliminate launch hesitation.
 
moparschmidty said:
fdrgator,
yes, "Holley Bog", experimenting with different carb accel pump cams for fuel used, weather, axle ratio, track conditions timing etc. for best launch. Eliminate launch hesitation.
Click to expand...

That bog is similar to what happens in an outboard. Not enough airflow through the carb venturi at low rpm when the throttle is suddenly opened. Cars compensate for it by using an accelerator pump. No accelerator pump on the outboard, so carbs don't fully open until RPM increases (by spark advance and limited carb opening) enough to make sufficient airflow through the venturis. Over simplified explanation.

I'm not blessed enough to own a Fluke. but DVA is a fancy way of saying Peak Reading Voltmeter. It holds the maximum voltage value for you to observe. A regular VOM cannot grab the very fast voltage peaks. A DVA adapter holds the peak for a regular VOM to read.
 
It holds the maximum voltage value for you to observe. A regular VOM cannot grab the very fast voltage peaks. A DVA adapter holds the peak for a regular VOM to read.
Well then the record functions of the Fluke Meters is exactly the same this, built in. The 87 has the better with 1ms snap shots, great for catching glitches in items like TPS sensors. So it will be the better tool to catch the values on the stator and timer base, and no need for another special tool.

If I cn find the paper I was taking values down with I'll post them, but it was not near the values posted on CDI for that series of engines.
Thanks again, I am loaded with enough to attack this thing again when spring comes, in JUNE!
 
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