Weak spark - sensor or powerpack

[bennysku]

I have a 1977 140hp Evinrude. I am getting intermittent spark. With all the spark plugs out I get spark on all cylinders. With them in I get intermittent spark. Overall the spark is weak. Battery fully charged, normal cranking speed, and new rectifier. I removed the flywheel and on the inside of the stator/timer base are two sensors. When I adjusted these closer to the inside of the flywhell I started getting a heavier spark, but to make it strong enough spark the sensors are touching the flywheel. Checking resistance readings look good. The sensors connect directly into the powerpack.

Is this a sensor problem or powerpack? Also I can't find those sensors for my year/model(140783s) anywhere.

 

[Joe Reeves]

Re: Weak spark - sensor or powerpack

The sensors are unavailable and always have been. To replace would necessitate replacing the complete timer base.

The engine must crank over at least 300 rpm in order to have the stator provide approximately 300 AC volts to the powerpack's capcitor. Anything less results in weak ignition.

If you have low cranking rpms with the spark plugs installed, find out why.... loose cable, tight but dirty cable connection, failing starter, etc.

The spark, with the spark plugs removed, must jump a 7/16" gasp with a strong blue lightning like flame..... a real SNAP! Does it?

 

[clanton]

Re: Weak spark - sensor or powerpack

Check the sensor air gap. www.rapair has a plastic tool for this.

 

[OBJ]

Re: Weak spark - sensor or powerpack

clanton you sonofagun!! where ya' been??d

 

[clanton]

Re: Weak spark - sensor or powerpack

I`m hiding out close to Panama City, just move into a 36 ft
Holiday Rambler fifth wheel , looking for a tow vehicle now. My blood pressure down, weight up, feeling great.

 

[OBJ]

Re: Weak spark - sensor or powerpack

Outstanding!!! Nice to see your smiling face again...d

 

[bennysku]

Re: Weak spark - sensor or powerpack

I found this:

CHARGE COILS
Charge coils may be checked by reading resistance between brown wire attached to terminal #7 and brown/yellow wire attached to terminal #8.

Correct resistance is 555-705 ohms.
There must also be infinite resistance between either lead and ground.

:::
The resistance between the brown wires is within spec, but I do not get infinite resistance between those and ground. Since the brown wires lead to the stator, should I replace the stator?

 

[Joe Reeves]

Re: Weak spark - sensor or powerpack

Infinite readings means that there should not be any reading at all. Is this what you're encountering?

If when checking between either wire and ground, any reading indicates a short (bad). No readiing indicates there are no shorts.

No intention of insulting your intelligence here, just a case of that sometimes things get confusing.

 

[bennysku]

Re: Weak spark - sensor or powerpack

Actually I get infinite readings when the wires are disconnected from the powerpack, but I do get readings when they are connected. Also the cranking speed is over 300 rpm. I do get spark w/ plugs out, but not with plugs in. I tested the volts coming out of the two yellow wires and the two brown wires. With plugs out and getting spark. The volts are still lower than expected.
I need to get a service manual. Trying to fix my issues w/o buying unnecessary parts.

 

[nate6231]

possibly running on 1 cylinder

possibly running on 1 cylinder

im test driving my uncles boat a 94 kenner pro skiff, w/94 evinrude -40. I changed the gas and plugs, it ran fine on the hose. I put in yesterday, full throttle was 9mph it eventully got up to 18 after a little while, it is supposed to go 35mph. back home, on the hose, with the motor running i disconnected the the top spark plug boot and it died, put it back on, restarted it, disconnected the bottom boot, it ran uneffected. i touched the disconnected boot, it shocked me and i could hear it sparking. any suggustions?

please help.

 

[mikesea]

Re: Weak spark - sensor or powerpack

nate,start your own post,your not going to get your message across to enough people on this guys post,but I suspect your carbs need cleaning

 

[Joe Reeves]

Re: Weak spark - sensor or powerpack

Benny.... As per your last post, the test for the spark, continuity, etc are all okay. You will obtain a reading when wires are connected as the continuity is then leading thru other components..... false readings.

If you have a strong blue lightning like spark when cranking with the spark plugs removed BUT not when the plugs are installed, that indicates that either the cranking speed is lacking somewhat OR the stator may be failing.

With a regular spark tester (7/16" gap) connected to the spark plug leads, and the spark plugs installed, hand crank the engine via a rope. If that test reveals a good spark, I'd suspect cranking speed.

 

[bennysku]

Re: Weak spark - sensor or powerpack

I'm going to replace the stator. The cranking speeds are fine and not too long ago I had to replace the recifier since the power lead fried. That could of possibly created issues back to the stator or maybe the stator created the issue to the rectifier.