Weak Spark Problem - 1955 Johnson RD17 25hp

[jb93]

All new ignition components and plug wires. Points new, clean and gap set properly. Armature plate grounded to block, as it should be. Top cylinder wire sparks intermittent. Bottom cylinder wire no spark. I have pulled flywheel 4-5x now to recheck everything and make sure points are spotless.

I decided to put wires on spark plugs and hold them against the block to see what happens. I have spark on both top and bottom this way.

There doesn't seem to be anything else I can do to address the spark to get it to jump 1/4". A friend suggested to gap my spark plugs at 0.025 instead of 0.030 and see if I can get it going that way.

Thoughts?

 

[scottmm73]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

Just because the ignition components are new doesn't mean they are good. I would go through and switch out each component, one at a time, with the same component from the known good side. Rules of deduction. You mention spark-plug gap but don't mention the spark-plug, are the spark-plugs new, have you swapped them out?

 

[jb93]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

Just because the ignition components are new doesn't mean they are good. I would go through and switch out each component, one at a time, with the same component from the known good side. Rules of deduction. You mention spark-plug gap but don't mention the spark-plug, are the spark-plugs new, have you swapped them out?

Good point. However, the "good" side really isn't 100% good. It sparks intermittently (maybe 50% of time) across 1/4" gap. I will swap the condenser and coil (separately) to see if my intermittent spark move to bottom cylinder. I'm not testing with spark plugs, just spark tester. They will be new once I get this spark sorted out.

 

[racerone]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

Coils ( air gap ) must be properly adjusted when installed.-------Points can be properly timed using timing marks on mag plate and flywheel.

 

[jb93]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

Coils ( air gap ) must be properly adjusted when installed.-------Points can be properly timed using timing marks on mag plate and flywheel.

I have the steel ring that sets the coils gap that is replication of factory tool by FR on this board. I am not sure how to do the flywheel timing. I just have gap set at 0.020. That should be close enough to get good spark though?

 

[racerone]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

Correct, there was no mention that you had set them correctly using that tool.

 

[scottmm73]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

What is the gap set on the spark plug tester?

 

[Daviet]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

You might also check the contact between the points base and the mag plate. I always use sandpaper to make sure the area is shiny to get a good ground for the points.

 

[HighTrim]

Re: Weak Spark Problem - 1955 Johnson RD17 25hp

Run a points file, or wet/dry wrapped around a hacksaw blade through the points many times, then dip a business card in acetone and run that through. Blow with compressed air to ensure to debris there. the things that will hinder spark you cannot see.

How are the magnets, if weak, will give you issues. Will the magnet pull a screwdriver in from about an inch away and hold it in the air?

Good continuity through the coil/plug wire/plug spring? Good connection at the spring?

Twist plug wire into coil to ensure good continuity there? You need to pull plug wire through mag plate, so there is plenty of slack, twist the coil onto the plug wire, then pull excess wire back through mag plate.

 

[jb93]

UPDATE.. I was never able to get the spark to jump 3/16 to 1/4 gap on tester, but if I ground plugs to the block it does fire. I was unable to get it started for a long time and just kept thinking it must be the weak spark. Coils were already new. I bought new points and condensers...again...and super shined the points with 1000 grit paper and cleaned with acetone. Still no spark at 3/16 gap, but plugs spark. I then found a picture of a magneto plate showing the ground wire of the coil going to the mounting side that has just one screw holding it down. I had that wire going to the mounting side of the coil with 2 screws. I switched it over to the other side and she started right up. Still have to tune the carb, but it starts. I guess as long as it runs then my weaker spark that won't jump 3/16 but will spark the plugs is what it is. Was it the moving of the coil ground wire to the correct side that got me going or just dumb luck???

 

[F_R]

I won't call it dumb, but I will call it luck.

 

[jb93]

I won't call it dumb, but I will call it luck.

So it didn't matter which side that wire was on? the pictures and diagrams I saw had it on the single screw side of the coil mounts.

 

[nwcove]

a ground is a ground.

 

[jb93]

a ground is a ground.

What a buzz kill. But I'll take the motor starting. Something happened and I did it. POW!!! Brilliant!!

 

[nwcove]

yep....now to bad you cant figure out why moving a couple of ground wires made the difference? (but it lives....thumbs up ! )