compression

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papasage

Senior Chief Petty Officer
Joined
Jan 12, 2003
Messages
785
1974 70 hp 3 cylinder 120 lb top 150 on other 2 cranks run good at idle sluggis at wot. breaks up at mid rpms . new plugs all plugs firing strong . my suspishon is stater
 
rolmops

rolmops

Vice Admiral
Joined
Feb 24, 2002
Messages
5,311
Re: compression

That hole that has 120 is trouble. Check it out. It may just be a stuck ring but that compression is way too low
 
B

boobie

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

30 psi between cyl's is to much. Pull the head and and see what you find.
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: compression

Before you tear into it do a decarb treatment then another compression test. Decarboning often loosens up stuck rings.
 
P

papasage

Senior Chief Petty Officer
Joined
Jan 12, 2003
Messages
785
Re: compression

last time out the #1cylinder went out no spark replaced the power pack and coil and all 3 plugs started right upon muff . the top plug was black even around the thread . the engin has not ben run a full tank sinse i had it torn down for new rings and crank and all berrings .was running on all cylinders but the crank was bad .
 
B

boobie

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

Take it to the water and run it. That is the true test.
 
B

boobie

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

When it's acting up pull one plug wire at a time and see which cyl is not firing. AKA Cyl drop test.
 
phillnjack2

phillnjack2

Ensign
Joined
Apr 30, 2011
Messages
918
Re: compression

good advice from above post.
you need to know whats firing properly and what is not.
if the engine has been rebuilt then dont expect the compression to be right untill its all bedded in properly.

tests tanks are fine for certain things, but nothing like a real river test to know a lot more about whats going on.


and please dont try it on your own, you need someone at the wheel at all times to be safe.
far too many people try it on there own and end up falling overboard with terrible outcomes.



phill......
 
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