compression..? does mine suck??

[lake_time_2]

Hi,<br />I have what I think to be ‘89 (OC136657) mariner 90hp (3 cylinder). I know enough about boats and motors to know that I know next to nothing … other then I think have picked up a dud.!! <br />Can anyone tell me what the compression should be?? Its 90-95-90 psi now and I’m guessing that that sucks. Also the motor seems to miss when reved. (the RPM’s seems to jump up 500 or so and down as well) I have only run it with a flusher on as I am scared to take it out and have to paddle back!!<br />I cleaned the plugs and gave it new gas and oil but no change… My next step is new plugs.. Is there somewhere I can look up what plugs it SHOULD have.?? I just don’t trust anything about this at the moment.<br /><br />Lastly what is the difference between Mercury and Mariner motors?… in particular my ’89…?? Is there any?<br /><br />Thanks as always in advance,<br />Dave

 

[miloman]

Re: compression..? does mine suck??

not bad I thinkth e compression on that motor should be in the 120 range the important thing is that the numbers are close to each other you might want to decarb it change the plugs

 

[RICKRICK1]

Re: compression..? does mine suck??

LT2<br /><br />I ditto miloman. I would decarb and if you can, do it in a barrel or just back into the water if marina is not busy. It's real hard to set idle on muffs(next to impossible)and get a true RPM reading. Also the back pressure of a barrel or in the water may remedy some of your RPM jumping around. Then recheck compression while motor is warm. Sounds like you just got this motor. I strongly recommend changing the impellar as soon as possible. PRECAUTION if decarbing on muffs make sure what ever is behind the exhaust is wash able as the exhaust can be pretty filty.

 

[lake_time_2]

Re: compression..? does mine suck??

Thanks for the suggestions.. How does one De-carb a motor? I have a pond on my property that I can plop the boat in (I was going to do this to work on the trailer anyway) but can you give this new chap some specifics.. PS thanks for the help rickrick1 the link to the mercury/mariner years in a earlier post was super.<br /><br />Dave

 

[DJ]

Re: compression..? does mine suck??

Lake time,<br /><br />I do not believe your engine is ill. The compression readings may be a bit low. The important point is that they are close to each other.<br /><br />For a decarb. procedure, go to the search section of this board and type in "decarb". Get a fresh cup of coffee and plan to do alot of reading.<br /><br />Yes, you can do it in the pond-great idea?<br /><br />I agree with the others that an impeller is due, if you do not know the history of the engine. A lower unit lube drain and refill is also in order.<br /><br />Performing these maintenance tasks may help get your confidence in the engine back.<br /><br />Good luck, we'll be here.

 

[miloman]

Re: compression..? does mine suck??

I agree with the impeller decarbing is a fun task awful dirty but fun as the others said search the board for decarb info it is very difficult to get any accurate reads on muffs I would drop it in the pond as opposed to the barrel and see if the problem is remedied I would be very very cautious as to how long you run this motor you sould change the impeller first prior to any long runs on the motor I would bet money that it is brittle and dont forget the first thing is wd40 in the cylinders change the lower unit oil and the gaskets for the drain and fill screw. then drop it in the pond for a short time let us know

 

[slow_boat]

Re: compression..? does mine suck??

Merry Christmas all!<br /><br />Laketime; I think djohns is telegraphing that it might *not* be the best idea to dump all the decarb gunk into your pond. It can be done in a trash can which can be dumped away from your pond. Djohns...not trying to clarify your point and let us know if you meant otherwise.

 

[radsrh]

Re: compression..? does mine suck??

I have to agree with slow boat on this one, unless this is a large pond with a source of fresh water like spring feed I would not recommend doing a 1st decarb in a pond. You neaver know just how much junk will come out the exhaust you might end up exxon Valdez floating around for a long time. The only other thing I would recommend is cleaning the carbs.

 

[lake_time_2]

Re: compression..? does mine suck??

thanks for the info... its pretty big but i can do it in a trash can the first time. Thanks as always. Dave

 

[Bear]

Re: compression..? does mine suck??

Decarb, how and why (click)