Is this low compression 3 hp Johnson JW 10

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fishon71

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I have an old 1953 Johnson JW 10 three hp that will not start - has good spark and super clean carb. The compression is 75 psi in each cylinder, is that too low? Has a tiny bit of life after 20 pulls some times, my arm is getting sore. I thought anything above 50 psi would run.
 
oldcatamount

oldcatamount

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Re: Is this low compression 3 hp Johnson JW 10

that's not to low, it should run with those numbers. You have other issues there. Mybe try not using the choke quite so much when cold starting. It's possible you are flooding the motor. Also be sure to have fresh fuel.
 
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fishon71

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Re: Is this low compression 3 hp Johnson JW 10

Thanks - What is a good starting point for the carb adjustments, I have them each one turn out now
 
oldcatamount

oldcatamount

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Re: Is this low compression 3 hp Johnson JW 10

Try 1 1/2 turns on the low speed needle. I think the high speed needle is one turn but not sure.
 
lindy46

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Re: Is this low compression 3 hp Johnson JW 10

Have you cleaned/replaced the gas filter on the on-off valve coming out of the gas tank?
 
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fishon71

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Re: Is this low compression 3 hp Johnson JW 10

Yes, and there is fuel in the bowl - will not even start if I spray a little mix into the carb, not even with starting fluid ( I know bad idea) last resort
 
oldcatamount

oldcatamount

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Re: Is this low compression 3 hp Johnson JW 10

It's got to be an ignition problem then. Points, coils, plugs. It could be that you have one bad coil but, You might as well do both.
 
Tim Frank

Tim Frank

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Re: Is this low compression 3 hp Johnson JW 10

Check spark using a spark tester....the spark needs to jump at least a 5/16" gap.
 
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fishon71

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Re: Is this low compression 3 hp Johnson JW 10

Spark looks good & strong on both plugs
 
oldcatamount

oldcatamount

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Re: Is this low compression 3 hp Johnson JW 10

Have you tried a "link and synch" adjustment, where the throttle cam roller reachs the timing mark at the same time the carb butterfly begins to open?
 
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DJ

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Re: Is this low compression 3 hp Johnson JW 10

75 psi is quite good.

Low speed about 1 1/2 turns out-as a starting point.

If your float is sinking (probably) you'll have to 1/2 choke it to get it going and stay running. Sounds backwards but is true.

The old cork floats had a habit of "sinking".
 
lindy46

lindy46

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Re: Is this low compression 3 hp Johnson JW 10

If you have spark, and you spray pre-mixed fuel directly into the carb, it should at least fire for a second or two. Try again, and if you get nothing, take a look at the spark plugs and see if they are wet or dry. If dry, then fuel is not being drawn through the leaf plate.
 
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steelespike

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Re: Is this low compression 3 hp Johnson JW 10

Are the coils new or have you checked the condition?Spark should be blue and have an audible snap.
Your flywheel key may be sheared.Just the slightest crease will throw off the spark.
You'll have spark but at the wrong time.Late.
 
Tim Frank

Tim Frank

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Re: Is this low compression 3 hp Johnson JW 10

Tim Frank said:
Looks can be deceiving...;)

How are you testing the spark?
Click to expand...

fishon71 said:
eyeball
Click to expand...


That probably hurts. :rolleyes:

If you are using a proper spark tester, great.
If you are just grounding the plug to the block, good luck.

You can read all the reasons why this is an inadequate troubleshooting method in a multitude of posts in these forums.
 
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fishon71

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Re: Is this low compression 3 hp Johnson JW 10

Okay pulled the flywheel and the coils are all dried out and cracked - most likely leaking. Now what is the pn for the coils and what year range will work. They look the same as stuff from the 80's
 
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fishon71

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Re: Is this low compression 3 hp Johnson JW 10

I have a bunch of used coils that look like these but no numbers - is it safe to say if they look the same & fit they will work okay? They might be from late 70's motors and bigger hp's?
 
meyerboy

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Re: Is this low compression 3 hp Johnson JW 10

oldcatamount said:
Have you tried a "link and synch" adjustment, where the throttle cam roller reachs the timing mark at the same time the carb butterfly begins to open?
Click to expand...

what is a "link and synch" adjustment?? is there an earlier post that explains this?..
Also, what do you mean by carb butterfly begins to open??? do you mean the reeds??

inquiring minds need to know.
 
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