1982 mercury 70 compression

[JUSMARCEL]

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

 

[aussieflash]

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.

 

[JUSMARCEL]

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.

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

 

[Faztbullet]

Re: 1982 mercury 70 compression

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

 

[Mi duckdown]

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]

Re: 1982 mercury 70 compression

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

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]

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.