1954 johnson cd-10 5.5 hp compression

Ray2

Cadet
Joined
Sep 26, 2010
Messages
16
hi, just got this cd-10 5.5 and it has been sitting for over two years or more,so i cleaned tank out real good and put new 16-1 gas in put in barrel started but would not stay running, very erratic would not , it has blue spark and pumps water ,so i thought before i got a carb kit for it i would check the compression on it first,so i rent one and screw in until snug,leaving the other plug in and pull rope 10 times and it shows 30 psi.then try the other piston and 10 pulls and it says 30 psi i have never done a compression check before and wondering if i 'm doing something wrong, i thought it should be at 80 to90 psi, then i seen somebody said as long as both had equal psi probably would be ok.any thoughts? thanks..
 

nwcove

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May 16, 2011
Messages
6,293
Re: 1954 johnson cd-10 5.5 hp compression

not very good numbers......try doing the test with both plugs out and pull it over as fast as you can without breaking the cord. the fact that its even is good, so dont give up hope, as many comp testers will give you drastically different numbers. 60 psi would be acceptable.

edit: welcome to iboats!!!!
 

Ray2

Cadet
Joined
Sep 26, 2010
Messages
16
Re: 1954 johnson cd-10 5.5 hp compression

not very good numbers......try doing the test with both plugs out and pull it over as fast as you can without breaking the cord. the fact that its even is good, so dont give up hope, as many comp testers will give you drastically different numbers. 60 psi would be acceptable.

edit: welcome to iboats!!!!
thanx for the quick
response, took both plugs out and pulled, still 30 psi,its a oem gauge set,should i try another gauge set before buying a carb kit,it was running 3 or 4 times for about 30 seconds,i'd hate to put more money in it if theres something bad wrong with it and my skill level is low, never worked on one before...
 

Daviet

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Sep 24, 2008
Messages
8,958
Re: 1954 johnson cd-10 5.5 hp compression

If it would start and run for 30 seconds, you have enough compression to make it run. I would put a carb kit in it and get it running and do a decarb on the engine and see if the compression numbers will come up.
 

Ray2

Cadet
Joined
Sep 26, 2010
Messages
16
Re: 1954 johnson cd-10 5.5 hp compression

If it would start and run for 30 seconds, you have enough compression to make it run. I would put a carb kit in it and get it running and do a decarb on the engine and see if the compression numbers will come up.
thanx,iwill get a carb kit, what does decarb mean? the guy i bought it from said it ran when it was put up,but he wasn't very clear how long that was,it also had a broken starter spring he didn't tell me about but i already fixed that, looks like i'm going to know this motor thru and thru,
 

lindy46

Captain
Joined
Nov 27, 2008
Messages
3,886
Re: 1954 johnson cd-10 5.5 hp compression

Just had a 3hp with 30psi on both cylinders. Would barely run. Replaced the head gasket (the old one was blown) and got 80psi on both cylinders. Now she runs like a top.
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1954 johnson cd-10 5.5 hp compression

A true 30psi would not be enough for the motor to run. Borrow another gauge, preferable a thread-in type and try it again...
 
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