Intermitent spark on 1968 5 hp johnson top cylinder only

[vzapp]

So here's the deal. Earlier I had posted problems with this engine being difficult to start while warm. Now the problem is that I only have sporaticly intermittent spark on the top cylinder. Here's what's been done so far to try to track down the problem:
1) All ignition related items have been either replaced or have been swapped from one cylinder to the other. Swapped the coils, points, plugs and condensers. No change.
2) Replaced the sparkplug wires with brandnew ones. No change.

The bottom cylinder has excellent spark. The top cylinder has an occassional sign of life with a somewhat weak blue spark. I'm sure my cordless drill is providing ample RPMs.

HELP!

 

[nwcove]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

have to ask....are you using a proper spark tester or holding a plug against the block? is there any slop in the mag plate?

 

[vzapp]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Holding the plug against the block. No descernable slop in the mag plate. I'm sure using a proper spark tester would be helpful in properly judging a spark. However, all I want to see is whether a spark is present. Plus. Through all of this the one thing that has been consistent is presence of spark on the bottom cylinder and an absence of meaning full spark on the top cylinder. Thinking that my "hold against the block" method might be the cause of the problem I've also fruitlessly attempted to start the engine.

 

[HighTrim]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Yeah bad bearing?

EDIT: Ok was typing at same time as you. No slop eh. Get a 5 buck tester and set it to 1/4". You might not have proper spark on either cylinder. Magnet ok in flywheel? Coil heel/magnet gap set? Points set to 020 and CLEAN!>? Coils aren't original are they?

 

[vzapp]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Will get a proper spark tester. Coil set flush with magneto base (boss?) new points set at .020 and cleaned with notebook paper. Coils are not original. Their outer casing is intact and undamaged. How do I test the flywheel magnet? Could this possibly be a timing issue? If so, what's the procedure for that?
Update: This afternoon I removed the magneto plate and cam to remove and clean the brass grounding ring and the other ring beneath that one in an effort to improve the ground. At first this seemed to help but the positive results soon faded. ??? Also, while I had an extra hand I manipulated the throttle back and forth while spinning the engine. This seemed to help a bit but not enough to end my quest for sufficient spark. I also temporaried an external ground with no positive results.

 

[nwcove]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

test flywheel magnets by dangling a screw driver about 3/4" away.....will the magnet pull the screwdriver from that distance? if not, slowly move in and do a guestimate of how close you get before it pulls in. ( 1/2" is bare minimum from my experience).
timing is set close enough for startup at 0.020 when the rubbing block is at the highest point on the cam.
clean the points with a piece of emery cloth folded over and pulled through a few times. then clean the points with a piece of paper that wont leave fibers behind, or use a buisiness card.

 

[vzapp]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Thanks NWCOVE, I'll test the flywheel magnet tomorrow. Base on your description of timing I should be good to go there. Double and tripple checked all of the above (minus the magnet). And if the magnet is weak? Replace the flywheel?

 

[HighTrim]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

I have to admit, weak magnet is very rare. I don't think I have ever personally encountered one myself.

Possibility though. Much more likely that there is still something wrong with the ignition components or setup.

 

[vzapp]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

High Trim,
I 've considered the possibility of faulty ignition components or set-up but I come back around to nothing having changed when all of the components were switched from one cylinder to the other. During my "wee-hour-can't-get-back-to-sleep" thinking last night I considered the possibility of oxidation underneath where the points for the top cylinder mounts. Today I'll do nwcove's "screwdriver dangle" on the magneto and remove and recheck the points. I can't believe how this simple ignition has stumped so many knowledgable people on this site as well as local folks in person.

 

[HighTrim]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Its a hard thing to diagnose over the internet with description alone unfortunately.

The main thing I find that has been done wrong is that the points are dirty. Even fingerprints limit spark. I dip a business card or paper stock in acetone and run that through after I gap and dress them.

Bad connection inside the plug boot?

 

[nwcove]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Its a hard thing to diagnose over the internet with description alone unfortunately.

^yep! kinda reminds me of the guy who called his doctor and said " doc, it hurts when i touch my foot, hurts when i touch my knee, hurts when i touch my elbow, hurts when i touch my nose" etc etc. doctor told him to come to the office right away!! turned out he had a broken finger.

(my attempt at humour is in no way directed at the op (vzapp), simply pointing out how difficult it can be to diagnose an issue from afar!! )

 

[HighTrim]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Another issue is what 1 man feels is satisfactory, another doesn't.

There was an iboater with a no start issue that we were trying to help. He had a late 50s Big Twin. He said he had adequate spark and compression. Well, he was in my area, so off I went with my tools to see this motor in person.

It had original coils, and 65psi in both holes. Someone on here told him that as long as it was equal it was ok. Well, that is baloney. That motor will not run with that low compression, equal or not. Will also not run with original coils. So, what we had thought was ok from his description, was in fact not.

Not saying this is the case here vzapp, not trying to imply you don't know what you are looking at, but mistakes get made in some circumstances.

 

[vzapp]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Halalulah. Finally soved the big mystery (though I must admit I'm a bit embarrassed to disclose the root of the problem).

I did the dangle test and passed with flying colors. Swapped condenser side to side and had temporary spark on the top cylinder. So off to Gwinnett Marine with old condenser and points in hand. Got a tune up kit and in passing asked the owner "How do these points look?" Not too bad but they aren't aligned real good, he replied. Well what causes that? I asked. He then mentioned the little clip that holds the spring from one side of the points to the base of the other side of the points. Hot damn. Bingo. By George I gotch'a now. There was no such clip on the points in my motor. So that little clip is very important to keeping the ground path secure. What I'd done is ***-u-me(d) that the person before me knew what to do and blindly followed their footsteps...down a long dark path. At any rate I asembled everything, spun the motor with my cordless drill and VIOLA! Spark on both cylinders. Put the (new) plugs in gave her a yank or two and she fired right off. Just damn.

 

[Daviet]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Glad you got it figured out, you probably helped some one with a future problem.

 

[HighTrim]

Re: Intermitent spark on 1968 5 hp johnson top cylinder only

Awesome. At least it was something minor. Enjoy the water now.