1994 Johnson 90hp Rebuild .030 Over Questions

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jammer729

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Well I started assembling my motor today and I was just thinking. If I am going .030 over on all 4 cylinders, do I need to change the carbs or jets? Also does this change the compression higher or lower? Is there anything else I need to be aware of? Thanks
 
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Haffiman

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Re: 1994 Johnson 90hp Rebuild .030 Over Questions

No need to change anything, but will highly recommend both carb rebuild and waterpump/thermostats when doing an engine rebuild.
Often a breakdown may not be engine related but caused by the boat fuel system so give that a good inspection as well.
 
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emdsapmgr

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Re: 1994 Johnson 90hp Rebuild .030 Over Questions

Agree. I believe you'd consider rejetting slightly if you went larger than .030 over. (.040 or larger)
 
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jammer729

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Re: 1994 Johnson 90hp Rebuild .030 Over Questions

Cool that will work for this motor. I do have carb kits, new water pump and stats as well.

I am also building another motor and one side the cylinders were ok so they were just honed but the other side had to be bored out. One cylinder is .030 over and the other is .064 over. I thought it was odd but the machinist said they do it all the time. How about that one as far as jetting? I would guess they would be ok as well cause you wouldn't want to run the stock cylinders to rich?
 
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emdsapmgr

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Re: 1994 Johnson 90hp Rebuild .030 Over Questions

You should consider rejetting the side of the carb that feeds the .064 over piston. I'd also be concerned if you are mixing pistons from more than one manufacturer in that block.
 
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jammer729

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Re: 1994 Johnson 90hp Rebuild .030 Over Questions

Two will be stock and just re-ringed and the other two will be wiesco's

I was told it would be ok if they were the same weight.
 
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emdsapmgr

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Re: 1994 Johnson 90hp Rebuild .030 Over Questions

I'd be more concerned about the different (heat) expansion rates from one mfg'r to the other.
 
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