what do you think about these compression numbers

[adk_vfr]

So I just bought a new boat so I had the compression tester out and that one tested really good. I was getting ready to put it away and said hey I should test the 90 on my bass boat for giggles. My bass boat has a johnson 1990 90hp j90tlesb and I did this test cold with the motor not being started since fall. Here is what i got left bank top #2 108 lb , left bank bottom #4 105 lb, right bank top #1 87 lb, right bank bottom #3 85 lb. the motor ran good for me all last year only issue I really had was she stall somtimes when at idle and switching from reverse to forward. sowhat do you guy think about the numbers I never started it and didnt wanna run water through it as its still very cold here in upstate NY.

 

[adk_vfr]

Re: what do you think about these compression numbers

im thinking head gasket or rings maybe

 

[racerone]

Re: what do you think about these compression numbers

The ring are easy to inspect.--On the side of the block you will see small covers.-Remove the 6 wee bolts and pull those covers.-This allows you to look in at the piston and rings.--Will cost a couple of gaskets at say 99 cents each.---Check that before the season starts !

 

[Solittle]

Re: what do you think about these compression numbers

decarb??

 

[boobie]

Re: what do you think about these compression numbers

Decarb is the best idea before you run off in the heat of the day. These motors were known to do that. Again, try a good DECARB first.

 

[appleo]

Re: what do you think about these compression numbers

Don't get all jumpy till you get it out and run it
A lot of those old v4s were 100 lb across the board

If you have an out of family reading after you warm her up..then report back

 

[emdsapmgr]

Re: what do you think about these compression numbers

Your engine has the low compression bathtub heads. I'm surprised you get over 100. Maybe your gauge reads a little high. It is not unusual to have compression vary maybe 5 lbs between heads, due to the way they are manufactured. Yours is more than that. In any event, a healthy engine needs to have cylinder compression within 10% of each other. Yours does not. Could be a bad head gasket on the low compression side... That would be a best case scenario. East to replace. I'd probably shine a pencil light into the spark plug hole and visually inspect. Pits on the piston crown and scuffing on the cyl walls would not be a good sign.

 

[boobie]

Re: what do you think about these compression numbers

Some OMC service manuals say no more than 15 PSI between cylinders.