compression test - fuel and ignition neccisary to disconnect ?

muncedog

Seaman
Joined
Nov 13, 2014
Messages
67
Hi all,
So I read the FAQ on compression test and I read my official Johnson service manual. The manual doesn't mention any funky means to override ignition or disconnect fuel and it also mentions set to WOT.

So which is right- perhaps the service manual is skimp on detail and assumes these things?

The motor is a 2000 Johnson 130hp. If anyone wants something from the manual let me know.
Cheers
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
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49,038
Do you have a kill switch? Just pull the cord like you fell out of the boat, that kills the ignition. I wouldn't worry about the fuel because it won't fire with the kill switch pulled. If you don't have a kill switch, somebody knows what to do.
 

GA_Boater

Honorary Moderator Emeritus
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Messages
49,038
Do you have a kill switch? Just pull the cord like you fell out of the boat, that kills the ignition. I wouldn't worry about the fuel because it won't fire with the kill switch pulled. If you don't have a kill switch, somebody knows what to do.
 

muncedog

Seaman
Joined
Nov 13, 2014
Messages
67
So I have heard this before, but I am a little confused as the manual states that the engine will still start without the kill-switch cable present (I guess safety if your stranded at sea!?)

But also, do you use the starter motor to turn it over, if so doesn't the kill switch in the case you mentioned stop that functioning?
 

muncedog

Seaman
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Nov 13, 2014
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No Title

Also, while I had these out for replacement, I thought i'd ask your opinion. I photographed the worse one with quite some erosion on the nut section - Im guessing this one was poorly electrically connected and thus the anode wasnt as effective or perhaps its just the oldest of the four!

As for the spark gap itself - it seems that its slightly eroded on the lead. Also being a 2-stroke I guess its hard to read anything from the condition of the insulator (which is consistent caramel coloured, rather than a lighter section in the middle)

Cheers,
Adam
 

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ronward

Petty Officer 1st Class
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Jun 24, 2013
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346
First off...plugs are cheap! If in doubt just replace them. Second...if you have a kill switch lanyard the motor should not start if its pulled out. Either by the key or jumping the solenoid. It will still crank but is not getting fire to start, the kill switch has "killed" the ignition. If it does start then the kill switch is NFG. Actually it won't start anyway because you have the plugs out and grounded when doing a compression test.
 
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racerone

Supreme Mariner
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Dec 28, 2013
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Throttle simply does not need to be open for a compression test on a 2 stroke.
 

F_R

Supreme Mariner
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Jul 7, 2006
Messages
28,195
All the talk about the kill switch is fine, considering the motor in question here. But better yet, concerning any engine is to simply ground the spark plug leads. That will always do the job, any motor. The reason for defeating the ignition is two-fold. One is to prevent damage to the ignition system and the other is to prevent starting a fire.

As already stated, it is NOT necessary to block the throttle open on a two stroke. But it IS on a four stroke.
 

Roberthill

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Dec 3, 2012
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317
To do a compression check , remove plugs .No need to worry about ignition .No plugs No fire .
 

F_R

Supreme Mariner
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To do a compression check , remove plugs .No need to worry about ignition .No plugs No fire .

Sorry, We are talking about real fire---like gasoline fire flames. Gasoline vapor blows out the spark plug holes when cranking, and a spark can set it afire with explosive fury. The dangling spark plug wires can supply the spark. That's why they should be grounded to prevent any sparking.

Believe me, I know. I was neglectful once (and only once) and didn't ground them and flames shot out at least 10 feet. Thank you Lord, I wasn't standing in the line of fire and the building didn't burn down.
 

boobie

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20,826
F-R, I was in the same situation once. And I said once. You always ground the plug wires when doing the compression test.
 

muncedog

Seaman
Joined
Nov 13, 2014
Messages
67
Thanks all. As for the spark plugs I am replacing but just wondered what insight you could get from the lead erosion/ colour?
Also no one seemed fussed about fuel disconnect? Going to change the small inline fuel filter ( in engine) so might run the compression test then while fuel is disconnected.

I don't have any grounding studs on the engine, so will either need to buy a tool, rig something up or be 110% sure kill switch stops ignition!

Cheers
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
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You don't need anything fancy. A set of wires with alligator clips on both ends will do it. Clip one end in the plug boot, and clip the other end to any convenient metal part on the powerhead. NOT to any electrical component though.
 
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