Motor opinion

[Seal2400]

I bought a mariner 200 EFI Magnum 99 model it has 93 lb on every cylinder, is this a good motor?

 

[Texasmark]

My service manual for 60 through 125 hp 3 and 4 cylinder 2 stroke, loop charged Mercs. says expect problems when compression is less than 120 PSI. I'd say you are problematic if you are conducting the test properly with accurate equipment.

 

[merc850]

It used to be said that if the cylinders are within 10 psi of each other you're OK,
so maybe the gage is not accurate.

 

[Faztbullet]

Has it been sitting?

 

[Seal2400]

Has it been sitting?

Yes

 

[Seal2400]

Yes it has been sitting, it sat so long when I tried to loosen the steering that the cable broke.

 

[Texasmark]

Before you take much stock in your compression numbers, you need to clean up your cylinders. I don't know if the EFI Magnum has pressure backed piston rings or not (like my engines mentioned) but if so they could be carboned up and not fully expanding to make the compression seal they were designed to make.

Sea Foam comes in a 16 oz. pint liquid for mixing with the fuel or an aerosol that can be sprayed into the air intake. It has a long history and is a very good engine cleaner for lots of things including cleaning up a stuck engine. The directions on the liquid can of 1 oz per gallon is for every day maintenance, not cleaning up an engine that has been sitting.

Google the word DECARB and follow the procedure. Maybe do it a couple of times. If you live in town do it when your neighbors are gone....... Then retake your compression numbers with accurate equipment used as directed. You may be pleasantly surprised at your numbers and performance.

While you are at it, replace the rubber impeller in your water pump and replace the oil in your lower unit gear box. New fuel filter(s) would also be a good idea and a new fuel line/bulb from the fuel tank to the engine. A manual will do you a world of good. I get mine off ebay.

 

[lprizman]

What he said^^^^^^
You need to clean it up thoroughly and new plugs before firing if up... it'll go...I have the 150 version...due diligence and you'll be fine

 

[QBhoy]

Amazing that it’s 93 psi on all 6. I’d 100% get another gauge onto it before doing anything else drastic.

 

[Faztbullet]

Before you do anything make sure you clean/drain VST and check that fuel pump runs. Replace all filters on engine and I would send the injectors off to be cleaned and balanced. Seafoam will not clean injectors as they have filter in them. Remove and send to Brucato

 

[flyingscott]

Why is 93 psi considered low for a V6? Since the only manual mentioned is for a I3/4 cylinder and those motors have NOTHING to do with a V6.

 

[lprizman]

Should be 100 minimum....and that's low

 

[flyingscott]

Should be 100 minimum....and that's low

Where does it say that? Give the OP the facts, Like where does it say that?

 

[ahicks]

Where does it say that? Give the OP the facts, Like where does it say that?

Right next to where it says low compression numbers should be verified with another compression tester, and compression tests should be done with the throttles wide open....

Facts are easy to find. Experience maybe not so much....

 

[Faztbullet]

 

[flyingscott]

Thank you Fatz at least now the OP knows where he needs to be with his compression #s.

 

[lprizman]

Where does it say that? Give the OP the facts, Like where does it say that?

Just from years of experience....I should of elaborated more.....

Fazt nailed it....thank you!!!

 

[Chris1956]

Compression gauges need to be accurate and reliable.

Most (due to their cheap construction), are reliable, but not accurate. That is that they show the same compression number, for the same compression pressure.

So, most often, if a motor's cylinders are within 10-15% in compression, regardless of the number, the motor is good.

 

[QBhoy]

My issue is around getting the exact same reading for all 6 cylinders. In all the engines I’ve pressure tested..I’ve never seen identical figures across all cylinders like that. So strange.

 

[BWR1953]

My issue is around getting the exact same reading for all 6 cylinders. In all the engines I’ve pressure tested..I’ve never seen identical figures across all cylinders like that. So strange.

Maybe try using it on a different engine? Lawn mower? Car?

Then see if it does the same thing with those.