1996 Mercury 125 ELPTO Compression Question

[mcagnew]

I just recently bought a used 1996 125ELPTO and I want to do a compression check on this motor, and want to know what kind of numbers I should be expecting. I am going to run the numbers cold, since I have no gas tanks in the boat currently. <br /><br />Thanks...<br /><br />Also if there is anything else I should look at please let me know. I plan on purchasing a mercury service manual on the motor for reference, but this has been bugging me and I want to make sure I am getting a good motor. <br /><br />Thanks<br />Mike

 

[trihuller]

Re: 1996 Mercury 125 ELPTO Compression Question

I was told the most important thing about compression is that the numbers are close on all cylinders. Within 5-10 psi of each other.

 

[05GlastronSX]

Re: 1996 Mercury 125 ELPTO Compression Question

anything above 100-105 is good. also these numbers should all be within 5-10% of eachother like trihuller said. my guess is that your 125 came stock w/ about 125-130 lbs of compression.

 

[WillyBWright]

Re: 1996 Mercury 125 ELPTO Compression Question

Just so you know, the motor has a personality quirk. It runs on 2 cylinders at ilde and all 4 above half throttle. It's at about 1/3 throttle where it can't decide whether to run on 2, 3, or 4 cylinders. It's about mpossible to maintain a constant speed. That's the speed where beginning waterskiers and wakeboarders run. It'd also be noticable on pontoons. Otherwise it's about the speed where you'd be plowing thru the water at sub-planing speed and nobody really operates there. Once on plane, it's great. And for trolling, they're fine. It's just that one quirk that aggrivates some people.

 

[Capt Ken]

Re: 1996 Mercury 125 ELPTO Compression Question

Ya best be finding why those two aren't firing. If those cylinders are running lean and you keep doing that, you'll be rebuilding it soon.

 

[Silvertip]

Re: 1996 Mercury 125 ELPTO Compression Question

Ken - that engine is designed to run that way. It's an annoyance in some applications, not a problem.

 

[05GlastronSX]

Re: 1996 Mercury 125 ELPTO Compression Question

the engine is commonly known as the 2+2 ken. as stated above, it is designed to opperate on 2 cylinders for the lower rpms and activate the other 2 once the rpms increase.

 

[mcagnew]

Re: 1996 Mercury 125 ELPTO Compression Question

well we did a compression check and it showed two cylinders at 122 & 125, the other at 130, and then 4th was at 80. So it is going back to the shop that sold it to us, for them to take a look at it. being a two-stroke, I guess it can only be a reed valve or a piston ring...am I wrong. <br /><br />also...I know the motor is a 2+2. how are the cylinders seperated as far as what two cylinders run on idle and which ones come in later.