'82 50HP Johnson Compression Question

[wavebuster58]

The motor seems to lose power after running WOT for about 15 minutes straight. I have been reading the forums about compression checks and decarbs. Today I did a compression check and the results were 120 psi on #1 and 145 psi on #2. I know that these should be closer together but it sure seems like good compression for the age. I put a little oil in #1 and it came up to 145 psi but after about 3 more checks it was back to 120 psi. I read today that nothing should be done until trying to decarb. I'm not against trying this but would someone please explain to me how this could help? The only thing that makes sense to me would be that the decarb would lower the compression in #2. Is this what I'm trying to do? What should the compression be? Thanks for any sense you can make of this.

 

[Walker]

Re: '82 50HP Johnson Compression Question

Carbon can and will build up in the ring grooves and can prevent the ring from expanding against the cylinder wall (Stuck ring) Decarbing will loosen and disperse the carbon, therby freeing up the rings to be able to flex like designed.

 

[wavebuster58]

Re: '82 50HP Johnson Compression Question

Thanks Walker<br />I was looking for one good reason to do this, I hate doing things that don't make sense to me. Do you think Seafoam is the way to go?

 

[dajohnson53]

Re: '82 50HP Johnson Compression Question

I tried the Seafoam pre-mix technique this weekend (see FAQ). Previously I had done the squirt-into-carbs treatment. I think the pre-mix style is much easier to do a thorough job. I have a hard time keeping the engine running and squirting carbon treatment consistently into three different carbs. It's just a hassle. I did not do another comp. test yet to see how effective it was (ran out of time). Hope to do that soon. But it sure did apparently burn out a lot of carbon.

 

[mcginleyc]

Re: '82 50HP Johnson Compression Question

Wavebuster, the reason the compression is bumping up on the low copression cylinder when you squirted oil in is that the oil is sealing the gap caused by the stuck rings. Then compression goes to 145psi, where it should be. It falls back down to 120 because the oil gets dispersed after the engine is turned over for a few seconds. When you do the decarb treatment, make sure the engine is up to operating temp. The warm engine will loosen the carbon better. Spray alot of the seafoam or decarb in when the engine is at fast idle. Repeat this process a few times.

 

[wavebuster58]

Re: '82 50HP Johnson Compression Question

Thanks for all the help and input. I'm going to try this decarb thing this weekend. I'll let ya'll know.<br /><br />Thanks Again