Compression for Johnson

[fishfinder221]

I have a 1987 225 Johnson<br />ran a compression check on it today and came up with 50 psi on all cylinders.<br />doesn't that seem kinda low?

 

[Hooty]

Re: Compression for Johnson

You're right, that's real low. Are you sure of the gauge, test method, etc? Has the engine been running?<br />What prompted the test in the first place? Bring us up to speed.<br /><br />c/6<br /><br />Hooty

 

[fishfinder221]

Re: Compression for Johnson

well i'm running that on a 20 stratos,<br />I have a 23p prop and only can turn 5700 rpms w/ the jackplate jacked to the sweet spot<br />and i can turn the flywheel by hand pretty easily<br />motor runs perfect, start good ,but has a little studder on take off and when punching the throttle<br />I was just doing a routine check of the engine.<br />the guy who had the boat before me had a 200xp on it and was running a 25p prop turn 6000 rpm's.<br />the speed difference between the 200 and 225 is four mph. that doesn't seem right to me.

 

[ob]

Re: Compression for Johnson

If the motor is capable of that I would double check compression readings using different guage or insure the one you are using is sealed off.

 

[fishfinder221]

Re: Compression for Johnson

a local boat repair shop told me that 75 psi is normal compression for that engine.<br />that doesn't sound right.<br />your opinion?

 

[wilde1j]

Re: Compression for Johnson

OMC V4 and V6's usually yield compression readings between 100 and 150 psig. I would suggest shooting some oil in each cylinder just before reading. If the compression reading go way up, rings are likely worn.

 

[ob]

Re: Compression for Johnson

That engine ,meaning older high hours , or that engine within good compression range? Readings closer to 100 are typical.Maybe its time for a decarb.

 

[fishfinder221]

Re: Compression for Johnson

Just decarbed about a month ago.<br />the 200xp has been bored .030 over and has 40 hours on powerhead.plus it's a big bore engine. I was thinking on taking the carbs and reeds off of the 225 and putting them on the 200.<br />any suggestions on that.

 

[fishfinder221]

Re: Compression for Johnson

He told me that the engine new has abiut 75 psi.<br />which i thought it was 100 psi also.

 

[clanton]

Re: Compression for Johnson

My thinks sos, are the 200xp when new may have had as much or more HP the the 225, and may have had 115/120 lbs compression. The 225 probley had 100 lbs when it was new, 75 lbs is low. 50 is lower. The 200XP may have the same carb or the same carb bore size as the 225.

 

[redddog23]

Re: Compression for Johnson

My 1987 225 test out at 95 to 100

 

[G DANE]

Re: Compression for Johnson

Hi Fishfinder 221<br /><br />I suggest you get another gauge and take a new reading. If you have a cylinder below 60 it usually doesnt fire at iddle. It seems to mee you should have lots of trouble starting with 50. besides at a compression that low they would be equal = gauge faulty .<br /><br />If you decide changes, it should at least be based on facts.

 

[shelbydriver]

Re: Compression for Johnson

I have a 88 johnson 175, did the compression, got around 80/90/s psi. I did it cold by accident and did not open the throttle blades. I found out the seal was loose on one cyl test where a rubber o ring was smashed upon screwing in the tester. I put on a new o ring and metal washer from an old spark plug and got an extra 20 psi on one cyl that looked to be reading low, whew... thought I had a weak cyl there for a minute. Would I get more compression if the engine was warm. I did not realize this error in testing untill the 5th cyl and said screw it .