johnson 25hp compression

[Burfster]

How much compression should I expect to have on a 1988 Johnson 25 hp outboard. I know there are variables, I was just kinda curious what the average should be. I have 80 in each cylinder at this time but I think that might be low. Thanks in advance for any input

 

[oldboat1]

Try another tester -- screw-in type with a pressure release button. Try it with all plugs out. Crank until needle stops and record result. Hot or cold doesn't matter, nor does throttle position. 80# is low. Look for 110-125.

 

[Burfster]

Try another tester -- screw-in type with a pressure release button. Try it with all plugs out. Crank until needle stops and record result. Hot or cold doesn't matter, nor does throttle position. 80# is low. Look for 110-125.

Thanks for the reply. I was using the screw in type. I figured that the compression was low, but I was hoping I could make it last until this fall and get a different one next spring.

 

[kbait]

If it idles very slow and steady, you are likely fine. Should probably replace head gasket in case it has a slight leak between cylinders, that can get worse in a hurry.. and you can inspect cylinder walls too..

 

[Burfster]

If it idles very slow and steady, you are likely fine. Should probably replace head gasket in case it has a slight leak between cylinders, that can get worse in a hurry.. and you can inspect cylinder walls too..

I have already replaced the head gasket a while back which made it much better. I I did notice though that although I had spark in number 1 cylinder it just wasnt firing correctly. I could take off the plug wire and there was no difference. But when I did that to number 2 it died. I pulled the plugs and they were pretty wet with oil. I decided to try a different route and I got a new 1 gallon gas can and filled it with the proper oil mix and straight unleaded fuel. When I started it up there was a big difference. It will now for the most part idle well and respond better to the throttle input. Any thoughts on that?

 

[CaptnKingfisher]

I have already replaced the head gasket a while back which made it much better. I I did notice though that although I had spark in number 1 cylinder it just wasnt firing correctly. I could take off the plug wire and there was no difference. But when I did that to number 2 it died. I pulled the plugs and they were pretty wet with oil. I decided to try a different route and I got a new 1 gallon gas can and filled it with the proper oil mix and straight unleaded fuel. When I started it up there was a big difference. It will now for the most part idle well and respond better to the throttle input. Any thoughts on that?

Sounds like you're running on one cylinder. You've got spark but is it strong and consistent spark (measure with an adjustable tester, how far does spark jump). If you're running on one (as confirmed by your cylinder drop test) I would methodically work through the ignition circuit to find out why you're not getting fire on that cylinder

 

[tphoyt]

You mentioned you replaced the head gasket awhile back. Did you retorque the head bolts after running for awhile?
If not you could be leaking by and that could be giving you the low numbers.
If it’s been a long while you may need to replace the head gasket again.
Lap the head as well while you have it off.
Also if you ran better with the new gas you may have to much oil in the old gas.
and of course track down your weak/ no spark problem.

 

[boobie]

Do a cylinder drop test on it.