Need Help -Johnson 70HP 1975 Outboard Shakes

[paulwang]

Johnson 70HP 1975 Outboard Shakes a lot especially when in low speed. I just bought her last week, got a lot helpful information from this forum!
Jobs have been done: 1) fuel pump works well, I tried to squeeze the bulb, it's sold hard; 2) Clean three carbs, it was clean, all jets are fine 3) bottom reed valve leak caused carb spitting fuel backward, fixed, still leak a little bit but not spit fuel back any more; 4) crankcase halves leak, temporary fix by applying Permatex Ultra Grey; 5) chokes and throttles look fine to me; 6) extra oil and Seafoam in ethanol free gasoline; 7) compression test: top 121psi, middle and bottom 115psi.
Does she sound like missing fires a little bit? spark plugs look fine but always appear wet, three of them I have checked a few times. Tested the spark plugs with spark plug tester, all three blinks fine.
Nee your help please!
YouTueb Link:

 

[racerone]

Do the following in order.-----Make sure throttle plates are closed at idle.-------Post the compression numbers first.-----Then see if spark jumps a gap of 3/8" or more on each lead.-----Then start motor with timing light hooked up to #1 cylinder.----Observe the flashing light.----Should flash steady.----Repeat with # 2 and 3 cylinders.-----These motors are known to have water leak into the cylinders via those 3 gaskets on the exhaust manifold.

 

[paulwang]

Do the following in order.-----Make sure throttle plates are closed at idle.-------Post the compression numbers first.-----Then see if spark jumps a gap of 3/8" or more on each lead.-----Then start motor with timing light hooked up to #1 cylinder.----Observe the flashing light.----Should flash steady.----Repeat with # 2 and 3 cylinders.-----These motors are known to have water leak into the cylinders via those 3 gaskets on the exhaust manifold.

Thanks for your help.
I adjust the linkage for throttle and choke, to my naked eyes throttles are closed.
Cylinder pressure seems fine, 121, 115 and 115psi from top to bottom.

SPARK PLUG GAPS is less then 1/8", much less than you said 3/8". They are

NGK 3579 BZ7HS-10 Nickel Spark Plug. The spec gap is 0.039" or 1.0mm from NGK website. Are they the wrong spark plugs for Johnson 70HP 1975? ​

I used spark plug tester, the blink are steady to me, all three wires tested.
I hope I don;t have any more leaks, too much work to do.

I searched website and found the Gap should be 0.03", pretty small, I think mine are OK.

 

[racerone]

Stated clearly---" see if spark jumps a gap of 3/8" or more "-----The test for spark gap has nothing to do with the sparkplugs you are using.-----Nothing to do with a cheap blinky thing either.------It is a maximum output test of the system !!----System is capable of jumping a gap of 1/2" if in good condition.----I started working on motors before that motor was built.----My ears tell me there might be an ignition miss.----Motor not running on 3 cylinders all the time.-----Does not sound like one in good condition to me.----And some will argue.----I suspect issues with compression.----Those numbers are low.-----Perhaps a bad gauge !

 

[paulwang]

Stated clearly---" see if spark jumps a gap of 3/8" or more "-----The test for spark gap has nothing to do with the sparkplugs you are using.-----Nothing to do with a cheap blinky thing either.------It is a maximum output test of the system !!----System is capable of jumping a gap of 1/2" if in good condition.----I started working on motors before that motor was built.----My ears tell me there might be an ignition miss.----Motor not running on 3 cylinders all the time.-----Does not sound like one in good condition to me.----And some will argue.----I suspect issues with compression.----Those numbers are low.-----Perhaps a bad gauge !

Check the spark plugs firing again. Found more problems already.
Only the bottom one provide steady and bright light.
Top and middle ones will light up a few seconds and stop a few seconds, then repeat. I don't think they go bad at the same time, not 100% sure.
I am thinking I need two new coils, and that will fix the problem.

 

[paulwang]

Updated:

I switch bottom coil and the middle one, by changing the terminals in power pack and switch the spark plug wires. The bottom cylinder still work fine, it is with the middle coil now. Can this prove the middle coil is good? The middle cylinder still has problem, the firing is not steady.
I thought it's may be the spark plug has problem. Then I switch the spark plugs. Now the bottom cylinder with both spark plug and coil from the middle cylinder works fine.

Then I thought the power pack or stator have problem? when I measure the terminals on the power pack for middle and bottom coils, and find out the three terminals supplying power to coils are connected. Is this correct? I get confused at this point.

The resistance of my spark plugs are 55, 110 and 150 ohms.

 

[paulwang]

Stated clearly---" see if spark jumps a gap of 3/8" or more "-----The test for spark gap has nothing to do with the sparkplugs you are using.-----Nothing to do with a cheap blinky thing either.------It is a maximum output test of the system !!----System is capable of jumping a gap of 1/2" if in good condition.----I started working on motors before that motor was built.----My ears tell me there might be an ignition miss.----Motor not running on 3 cylinders all the time.-----Does not sound like one in good condition to me.----And some will argue.----I suspect issues with compression.----Those numbers are low.-----Perhaps a bad gauge !

Hello Raceone,
I bend the gaps to 3/8", the motor won't start at all. Then I bend the gaps back to 1/8". She starts but still runs rough. Does this indicates the voltage received by spark plugs is not high enough? Will mostly power pack problem or stator problem?

 

[racerone]

Sorry----I clearly stated that sparkplugs are not used for this simple test.

 

[jimmbo]

Bent the Gaps to 3/8"? What did you bend? There are Spark Testers made for that

 

[paulwang]

Bent the Gaps to 3/8"? What did you bend? There are Spark Testers made for that
View attachment 361717

I don't have one of the above tool, will get one soon.
Thanks for your suggestion.

 

[racerone]

You could make something with piece of plywood and some wires.----Glue the wires onto the plywood with a 3/8" gap between.

 

[Thirsty Endgrain]

You could make something with piece of plywood and some wires.----Glue the wires onto the plywood with a 3/8" gap between.

Jumping in to ask: is there a specific type of wire that is best for this? Steel? Al? Cu? Does the gauge matter? I got one of those cheapo's in the pic above and it flew apart the first time I used it, so I would probably opt to just make one to test again.

To the OP, it's said above but the spark plug test is to test your coils, you don't want to bend your plugs that far in and out of adjustment, all the spark needs to do is jump between to conductors, though I don't know what materials are best to use for that...

 

[racerone]

Any kind of wire ( cord from the toaster you are throwing out ) will work.----I have been doing this testing for 50 + years.----Some folks are going to learn tomorrow.

 

[Bayfisher Dave]

Hello. I would like to refer back to one of your statements that the plugs get wet/damp. In the video I see the throttle straight up in neutral/idle. Bit the carb throttle plates on all 3 are at full throttle wide open. They should be closed at idle. Can u get the to close at all? That motor should be screaming with carbs wide open. O would get manual handy and check the basics.

 

[Bayfisher Dave]

Hello. I would like to refer back to one of your statements that the plugs get wet/damp. In the video I see the throttle straight up in neutral/idle. Bit the carb throttle plates on all 3 are at full throttle wide open. They should be closed at idle. Can u get the to close at all? That motor should be screaming with carbs wide open. O would get manual handy and check the basics.

Also you said carbs/jets were clean but are floats adjusted properly?

 

[racerone]

What??----I see choke plates open.----Can not see throttle plates in the video at all !!!

 

[ct1762@gmail.com]

if spark follows the coil, might be a clue here. clean all coil connections and grounds until shiny. you could do resistance tests on coils. takes maybe 1 minute for all 3. i'd pull the head and check for water intrustion with that old 3 piece exhaust!

 

[paulwang]

Also you said carbs/jets were clean but are floats adjusted properly?

I didn't take out the jets (main jets), just clean it. I have just upload updated video after installing new power pack and one new coil.

 

[paulwang]

What??----I see choke plates open.----Can not see throttle plates in the video at all !!!

Maybe it's not a good angle. all three throttle plates are closed. I have updated new video after installing power pack and one ignition coil. How do you think the sound now.

Installed one new coil first, tried, it's still as before. then I installed the new power pack, the following video is the most recent one. Can't find my tachometer, it seems to me the idle speed is pretty high, throttle plates are closed.

UPDATED VIDEO: can I call it a fix?

 

[paulwang]

Hello. I would like to refer back to one of your statements that the plugs get wet/damp. In the video I see the throttle straight up in neutral/idle. Bit the carb throttle plates on all 3 are at full throttle wide open. They should be closed at idle. Can u get the to close at all? That motor should be screaming with carbs wide open. O would get manual handy and check the basics.

Thanks. As Racerone indicated these are choke plates not throttle plates.