Problem with 1976 johnson 25hp

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Fatlineman55

New member

• Jun 5, 2020

• #1

I recently bought a 25hp johnson model number 25r76e. Took it out to the lake and it is out performed by my 81 9.9hp. It seems like it takes forever to get up in revs and tops out at 15mph on 16 flat bottom, while the 9.9 does 16mph. Carb is clean and float works, fuel pump screen is clear. I'm completely clueless, any ideas would be very helpful!

 

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racerone

Gold Medal Contributor

• Jun 5, 2020

• #2

First thing to do is a compression test.----Then see if spark will jump a gap of 5/16" ( 8 mm ) or more.------I say it is running on 1 cylinder !

 

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Fatlineman55

New member

• Jun 5, 2020

• #3

Compression is 120 and 115. I do know they are both getting spark but how do make sure it's getting the 5/16" you say it should.

 

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racerone

Gold Medal Contributor

• Jun 5, 2020

• #4

May fuel pump diaphragm is ruptured.

 

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Fatlineman55

New member

• Jun 5, 2020

• #5

If the diaphragm is ruptured would I have to by a whole new assembly? And is that something you can take apart to look at it?

 

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racerone

Gold Medal Contributor

• Jun 5, 2020

• #6

Sure take it apart.----If it is the wee square pump the diaphragm is about $4.00.-----If primer bulb does not go hard a bad pump is a possibility.

 

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Fatlineman55

New member

• Jun 6, 2020

• #7

I had time today to take the fuel pump off. Upon breaking it down I noticed there was a spring laying on its side against the outer diaphragm. Could that be the issue?

 

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racerone

Gold Medal Contributor

• Jun 6, 2020

• #8

Could be.----A factory rebuild kit might come with instructions.------Is it a small pump ( 1-1/2 square ) or another type.

 

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Fatlineman55

New member

• Jun 6, 2020

• #9

Yea it is the small square type they used for a bunch of motors, the spring for the back diaphragm decided to pop out and is somewhere in my garage not going to look for it so just bought a replacement pump. Will update when I get it installed