1982 mercury 70 compression

J

JUSMARCEL

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Jan 31, 2012
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Hello evr1 as i am new to this forum, i bought a bass boat with a 1982 merc 70 on her, 3 cyl 2 carbs. I paid a big marine shop to pull carbs boil and put back on, they now tell me my comp. Readings are as follows: Top- 140 middle- 105 bottom _ 135, will decarb help to raise center comperssion? Thanks for yur time. Marcel
 
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aussieflash

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Re: 1982 mercury 70 compression

You want them within 10% of each other,so middle should be above 125 ish.I would buy a comp tester and do another test.Decarb may change results.
 
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JUSMARCEL

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Re: 1982 mercury 70 compression

aussieflash said:
You want them within 10% of each other,so middle should be above 125 ish.I would buy a comp tester and do another test.Decarb may change results.
Click to expand...

Any particular comp tester? and is there any diff between ngk buhw & buhw-2 plugs?
 
Faztbullet

Faztbullet

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Re: 1982 mercury 70 compression

Most good shops would check the compression before any work or troubleshooting is done to a engine......
 
M

Mi duckdown

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Re: 1982 mercury 70 compression

I agree with Faztbullet about the compression issue. BUT.. did you just tell them to rebuild the carbs??
THey should mentioned taken compression first.
Not taking sides at this point.
 
MassillonBuckeye

MassillonBuckeye

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Re: 1982 mercury 70 compression

JUSMARCEL said:
Any particular comp tester? and is there any diff between ngk buhw & buhw-2 plugs?
Click to expand...
Just for reference, I just tested the compression on my 1978 700 70HP and all three were right around 120psi. Not a very fancy tester. Used the method described here. Warm engine, removed all plugs, seated test plug lightly, cranked engine a few times.
 
ajgraz

ajgraz

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Re: 1982 mercury 70 compression

I have a kit like this one:
http://www.harborfreight.com/compression-test-kit-66216.html

My 1979 3cyl 70hp Merc also gives 110-120 on each cylinder, warm and all plugs out.

Was your compression test done warm or cold? If cold, it means nothing. Also, a decarb is not going to raise your cyl 2 compression, but it might lower the cyl 1 and 3 numbers so that all are more even.
 
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