Spark Gap Test Question

I saw someone ask about this the other day but never really saw an answer, sorry if it was.

When doing the spark gap test I set the tester to 7/16" and verified that the spark jumped the gap on all 4
cylinders. Is it important what color it was or is it just making sure that the spark can jump the gap?

The color of the spark while jumping was a lite blue. Is this sufficient? Motor is a 87 Johnson 88HP SPL(J88MSLCUS).

I've been fighting a no power problem under load. Following has been done:
2 new powerpacks( 1 of them was bad so I decided to do both)
4 new coils
New Plugs and wires and gas. Compression is 140 pounds on all four cylinders.
Temps on all 4 cylinders seem ok. Water pump was rebuilt earlier.

I have the 2 carbs torn apart now. I don't see any real varnish or plugged orifices, so I'm not sure this is the problem.
Going to rebuild them anyways so that I know what I have. Plan to rebuild the fuel pump also since the carbs are off.


Does anyone have any other ideas on what to look for if rebuilding the carbs doesn't help? I doubt I will be
able to get the boat back in the water this year. Was thinking I could check out other possible causes over the winter.


Thanks in advance
Jerry

Re: Spark Gap Test Question

Hi Jerry. Yes, you want a nice bright, blue, "snapping" spark that can jump 7/16"-1/4" gap. It sounds like you have the basics (good compression, strong spark, clean fuel system), but I suspect that you're still dropping one, or more cylinders while under load which is why your performance is suffering. This is usually due to a faulty, or failing ignition component, particularly when the motor gets warm. Your motor uses an electronic ignition system comprised of several black boxes filled with voo-doo and magic beyond my expertise, but I'm sure others will chime in with more help. There are inline spark testers you can use to diagnose the problem that flash every time the plug fires. You simply hook it to each lead and run the motor normally for a bit. If you fail to see the light flashing, then that means the cylinder is not getting adequate spark. You can usually find the testers at any auto store for about $5. Good luck. Keep us posted.

Re: Spark Gap Test Question

jerryny said:

When doing the spark gap test I set the tester to 7/16" and verified that the spark jumped the gap on all 4
cylinders. .....The color of the spark while jumping was a lite blue. Is this sufficient?

Click to expand...

That sounds like it's ok.

I've been fighting a no power problem under load. Following has been done.......Does anyone have any other ideas on what to look for if rebuilding the carbs doesn't help?

Click to expand...

Well, what exactly is the engine doing? Has it just started acting up recently?

Have you checked the timing? Have you done a link-n-sync? Verified that the timer base is rotating easily?

Re: Spark Gap Test Question

metriccrescentwrench said:

That sounds like it's ok.





Well, what exactly is the engine doing? Has it just started acting up recently?

Have you checked the timing? Have you done a link-n-sync? Verified that the timer base is rotating easily?

Click to expand...

The engine idles fine. But when I put it in gear I have no power. The engine doesn't die there just doesn't seem to be any power. When he first got the boat it would run like a champ for about 10-15 minutes and then lose all power. The last 2 times out there was no power from the get go. Just starts and idles fine. One of the times we were out we installed 2 inline spark testers. It seem to be firing on all four cylinders which is why I was wondering if maybe the spark isn't strong enough. Enough to idle but not enough to power the boat. My spark was not a deep blue when I ran the spark gap test.

I have the service manual. I see how you do a synch and link adjust.
Does the flywheel have to be removed to check if the timer base is rotating?
I have a timing lite. I will check the timing.

Is there any special order these tests should be done in?

I am very familiar with timing and such on older cars. In fact I own a 73 Triumph TR6, which I keep running. I'm just not knowledgeable about 2 strokes.


Thanks Jerry

Re: Spark Gap Test Question

When you advance the throttle, does it rev up at all?

Re: Spark Gap Test Question

HighTrim said:

When you advance the throttle, does it rev up at all?

Click to expand...

in neutral it does.

Re: Spark Gap Test Question

Sounds like timing to me, easy to check. Go the the "Top Secret" file and read up on Joe Reeves timing method. Good luck.

Re: Spark Gap Test Question

When you changed the coils did the clips or plug boots get mixed up. I am not an expert on your motor but I believe the powerpacks will determine the timing of the spark but if the timed spark is going to the wrong cylinder your timing will be off dramatically. It only takes one set to be mixed up to lose top end power.

Re: Spark Gap Test Question

retiredfornow said:

Sounds like timing to me, easy to check. Go the the "Top Secret" file and read up on Joe Reeves timing method. Good luck.

Click to expand...

Thanks

Re: Spark Gap Test Question

OptsyEagle said:

When you changed the coils did the clips or plug boots get mixed up. I am not an expert on your motor but I believe the powerpacks will determine the timing of the spark but if the timed spark is going to the wrong cylinder your timing will be off dramatically. It only takes one set to be mixed up to lose top end power.

Click to expand...

Thanks for the input. Yes I verified that the wiring is correct. Orange wire with blue stripe goes to the top coils on my engine.