weak spark?

[cesandroid]

Just wondering what a proper spark should look like. I have a Johnson 70 HP and when testing it the spark jumps the gap on my tester but very thin and not a big snap but it does jump the gap. Reason I ask is I'm having trouble starting just after its shut off for a few minutes. Sometimes it'll start rough, or when I start it I have to have the warm up lever to the max which even than it barely starts. I'm thinking stator as the plugs coils power pack and timer base were changed. The stator looks fine and ohms at 538. Disconnecting the charge wires makes no difference and the key switch seems to be OK as I ohm tested it as well. Thanks

 

[racerone]

Does the spark jump a gap of 7/16" on a test device, yes or no ?-----And what year is your motor ?----Model # is ?------What are the compression numbers ?

 

[cesandroid]

Yes, 1985 Johnson 70 HP, 115 compression even.

 

[racerone]

I do not believe there is anything wrong with the ignition system.-------But I do believe that compression is low.----Perhaps try another tester.-----Are you pushing the key in while cranking it over to start this motor when cold ?

 

[cesandroid]

Yes I do push the key in. It starts good when cold.

 

[cesandroid]

Can anybody describe to me a proper spark with a tester? just would like confirmation. Thanks

 

[Bosunsmate]

Sounds like you are doing it right but the appearance of a spark is subjective. I like it very bright, it sounds like yours is a bit faint.
Hard to know, it may be your issue. although often motors are hard to restart after being hot, fuel evaporates inside them, almost like they get flooded.
Its the only time i get a bit ancy when out at sea (concerned a long start will drain the battery), the cold start up never minds me

 

[cesandroid]

Gonna see if I can track down a good used stator. My service dealer doesn't have any in stock as this seems to be a hot commodity for this model. As for the compression, its even but a bit low i think as this is a rebuilt powerhead. Only a couple of hours on it so i'm guessing it should improve a bit over time. Its got WSM pistons and rings in it if that means anything.

 

[oldboat1]

Have a feeling there is more to the story than you want to let on, for some reason. Here is an effective open air adjustable tester (the kind to use):

Spark should be visible and noisy (snap). If it seems weak, reduce the gap on the tester and try again. Keep in mind that the starter has to spin the motor over at 250-300 rpm for starting. Test with all plugs out.

 

[cesandroid]

OK thanks, I do have a similar tester. Will do it again.

 

[racerone]

If spark jumps a gap of 3/8" ( 1 cm ) your system is producing around 30,000 volts.-----A test procedure must be developed to trouble shoot your motor.-------One with the motor cold / first start attempt of the day.--------Sparkplugs in and then do you get spark at 7/16" on your gap tester.-----Repeat that same test when motor is warmed up and refuses to co-operate.-----Take ohm reading on the stator when motor is warmed and refuses to obey your command to start.

 

[cesandroid]

Sigh!! You know I think this motor is hooped. Its got 2 hours on the rebuild compression is 112, 110, 100. The engine was bored and honed to spec they say, we assembled it carefully and everything was smooth going back together. All new bearings wsm pistons and rings. What are the odds of improving on break in, hmm, oh well run it till it quits I guess. A gamble on money probably lost in the short term. Maybe that's why its not hitting when hot.

 

[racerone]

Tell us more.----Running with VRO or just a plain pump and mixing at 50:1 on it and 25:1 for break in , I hope.-----Was the cause for the need to rebuild determined and corrected ?)

 

[cesandroid]

Its a newer vro pump plus 50:1 in the tank. Not sure if the cause was corrected as I got the boat with the damage done I believe unless the new pump is failing but the primer bulb seems fine. mechanic told me from being too hot. New water pump, and thermostat. It pumps good and feels alright on top the block. The manifold plates were checked as well.

 

[racerone]

Grommets for the poppit valves replaced and corrosion removed there ?----Overheat horn tested ?

 

[cesandroid]

horn was tested everything was clean before reassembly. If you're referring to those 2 springs than no, they weren't changed.They seemed ok but whose to say. Maybe that's the problem, what other symptoms would show up? Maybe i should look through the plug holes and see if there's something visual on the cylinder walls.

 

[cesandroid]

Took the thermostat housing off and everything looks good, the grommets are in place, the poppet valves as well as the springs seem fine. No rust or corrosion. Now for possible bad news, looking through the plug holes with a bright flashlight, I can faintly see what looks like some lines along the cylinder walls that run up and down about the same on all 3 cylinders. Not sure if that's scraping or if the lines are smooth or if this is part of the break in. Again only about 2 hours on the rebuild. The pistons have this black coating on the sides to help minimize scoring I was told. I talked to the machine shop and they said if its running good to just run it. I believe I can still see the crosshatch but its hard through a plug hole. Not sure what to do at this point if I should leave it alone and do what they say or tear it apart again. Isn't wall scoring due to either lack of lubrication or overheating or maybe they didn't get the ring clearances right. In either case I'm doing what I'm suppose to be doing with the motor.

 

[racerone]

It will cost you a head gasket ( $30 ) , to have a look in there.------Cheap in my opinion.

 

[cesandroid]

I also checked the spark when the motor is cold and the spark seemed ok. Here is a pic of cylinder 2. All cylinders appear the same. I can see the crosshatch and the lines I can't catch with a finger nail. Please comment. Thanks

 

[racerone]

Opinions will vary.----That motor needs to come apart.