Compression results

gustafsonerik

Petty Officer 1st Class
Joined
Jun 25, 2006
Messages
238
76 70hp rude cold compression with plugs out is 120,120 and 92 runs ok and I can get to wot but stalls sometimes then is hard to start when warm is compression the problem or something else???
 

oldcatamount

Lieutenant Commander
Joined
Apr 4, 2010
Messages
1,740
Re: Compression results

The cylinder with 92# wouldn't neccessairly cause the motor to stall or be hard to re-start, however, that's too much difference with the other two pistons to ignore. I'd pull the head off and look at the cylinder walls of that cylinder and look closly at the head gasket. Maybe it's just a bad gasket and an easy fix.
 

eavega

Lieutenant
Joined
Apr 29, 2008
Messages
1,377
Re: Compression results

I had a '76 70 HP Johnson, and as long as I owned it, the bottom cylinder was always a little low compared to the other two. That having been said, that is too much of a discrepancy between the one cylinder and the other two. Try a decarb and re-test compression.

Rgds

Eric
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: Compression results

As said above, give it a good decarb and check the compression again. You may have some ignition probs if it acts up when warm.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: Compression results

Get a spark tester and set it to 7/16" open air gap and check the spark when it acts up.
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,679
Re: Compression results

Old or incorrect spark plugs is often the cause of your complaint.
 

gustafsonerik

Petty Officer 1st Class
Joined
Jun 25, 2006
Messages
238
Re: Compression results

Ok I'm going to tell ya what happened to this motor,wether you believe me or not that's up to you,thanks to my 94 year old grand father,he told me a story that he had a 58 seahorse and the compression was so bad that if you put it in forward you could spin the prop without any resistance,he used a product called yale overhaul pellets in it,and got 3 more years out of it,thinking he was full of it,he gave me some of these little black pellets that looked like bronze powder and some sort of black lead in them,they were in a package that was from 1978,I followed the instructions that said put them in the spark plug hole,start it run it 15 minutes and let it sit,then run it norm
ally,took it out today and it ran flawlessly,I mean no proplems at all for 4 hours on the river.i let it cool down checked the cold compression and it's now at 105,I'm really interested to see how long it stays this way,I wanna take it out again next week and compare the compression again
 
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