Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

[Adder]

How do I determine if my engine is a 2-stroke or a 4-stroke? I haven't done much boating since I was a teenager when all outboards were 2-stroke which required an oil/gas mixture. I bought a 2003 Mercury 25hp tiller with electric/pull start - serial number 01673444 (with a full tank of gas) about two months ago along with a new 16' Jon boat and trailer. When I purchased the setup, I was told the engine was a 4-stroke.

I started having a few problems with it on short jaunts back and forth to my cabin on the Susquehanna River which is less than a two minute ride from shore. At first it would just die suddenly, especially at full-throttle, and then I would have trouble getting it started again. I figured the gas had ethanol in it so I replaced the gas with non-ethanol. For a short while it ran fine again but then I started having problems with it not starting or stalling in neutral so I adjusted the idle screw. Again it seemed to run OK for a while.

This past weekend for the first time since buying the boat, I made a longer trip down the river. The trip down had been at about one-third of the top speed because I was looking for a particular cabin and the engine gave me no trouble at all, but when I headed back, I opened it up to almost full-throttle. Within a minute, the engine suddenly revved higher and then died. Trying to start it again, all I got at first was a clicking sound. After a short period, it finally began trying to turn-over but wouldn't start. When I finally did get it started about five minutes or so after it died (I had to start it in gear, it wouldn't start in neutral), it was revving very high but with little thrust as though something was slipping. I limped back up river at low throttle with the engine periodically sounding normal and giving thrust and then revving high again with very little thrust.

I'm hoping and praying that I wasn't misinformed about this being a 4-stroke since I have been running it all this time with no oil in the gas. Again, how do I determine if it is 2-stroke or 4-stroke?

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Maybe I got a bit long-winded in my initial post and that's why there has been no replies. I'll consolidate and ask a few straight questions here. In reference to a 2003 Mercury 25hp tiller with electric/pull start - serial number 01673444...

• IS there a 4-stroke version of this engine? (I can't seem to find any reference to one anywhere. )
• If there is, how do I tell if mine is a 2-stroke or a 4-stroke engine?
• If it's a 2-stroke, what is the proper fuel mixture?
• If it's a 4-stroke, where is the oil added?

If it is indeed a 4-stroke (as opposed to a 2-stroke in which case I probably burned it up with no oil)...

• What could be causing it to suddenly die when at or near full-throttle? When this occurs, there is a clicking sound at first when trying to restart the engine and then after about five minutes it will usually start but often not while in neutral.
• What could be causing it to be hard to start in neutral when the engine is warm?
• What could be the cause of the motor intermittantly revving very high with little thrust and then 'catching' and running normally for a while with proper thrust?

 

[PS94]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

wow. does it have valves? is there motor oil to change? a dipstick or site glass? you got a picture of the motor? that might be a start....It's actually kinda a rediculous question...but to a neyophite to motors, it's a pretty honest question...

Sounds like it's overheating, to the point of siezing; which, might be from lack of oil, or, a water system problem...

if you don't know if it's a 2 or 4, run premix, as it really won't hurt the 4 stroke with it, might foul a plug, but that's better than running a 2 stroke with no oil, no?

 

[Fuzzytbay]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

I don't know if you have a 2 or a 4 stroke motor, but I have not seen any outboard four strokes, that don't say "four stroke" on the cowling somewhere.
I also havn't seen too many 2 strokes run for all that long without oil, at WOT.
Seems to me the motor has a problem, possibly not induced by lack of oil in the tank.

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

wow. does it have valves? is there motor oil to change? a dipstick or site glass? you got a picture of the motor? that might be a start....It's actually kinda a rediculous question...but to a neyophite to motors, it's a pretty honest question...

Sounds like it's overheating, to the point of siezing; which, might be from lack of oil, or, a water system problem...

if you don't know if it's a 2 or 4, run premix, as it really won't hurt the 4 stroke with it, might foul a plug, but that's better than running a 2 stroke with no oil, no?

I don't have a pic but I could get one tomorrow if that would help, and there is no dipstick or site glass that I could see. I know it's a ridiculous question and I felt like a fool posting it but as I said, its been a long time - over thirty years - since I've been boating. When I was younger, I could keep an old Evinrude running good enough to get around (my Dad owned and operated a boat and marine engine repair shop when I was real young and he taught me a few things) but with the new 4-stoke engines, I'm lost right now. When the guy sold me the setup (I bought it at a local marina and the engine came from his friend who works at a well known boat and engine dealership/marina) I took his word that it was a 4-stroke. He said that his mechanic had checked the engine and it was ready to go. Since my trips back and forth were so short (I haven't even used a half tank of gas yet), I just never gave a thought to checking the oil.

I'll get some premix tomorrow and give it a try, if the engine even starts. I did call a marina close by to get it in tomorrow, but they said their service orders are running up to three weeks right now and that just isn't acceptable. I need my boat running NOW.

I don't know if you have a 2 or a 4 stroke motor, but I have not seen any outboard four strokes, that don't say "four stroke" on the cowling somewhere.
I also havn't seen too many 2 strokes run for all that long without oil, at WOT.
Seems to me the motor has a problem, possibly not induced by lack of oil in the tank.

There is nothing on the cowling besides Mercury and the red stripe logo. As for running at WOT, I've only done so maybe three of four times because my trip across is so short and after the first time it died, I've been a bit cautious. I had planned on having a mechanic take a look at it, but didn't think it was anything real important or pressing since it seemed to run fine at about two-thirds throttle. Your last assumption is what I was thinking too until this last episode when it was revving so fast with no thrust. Then I started doing some thinking and the 2-stroke/4-stroke issue started eating at me, hence my post here.

From my description of what the engine is doing, do you have any suggestions as to what may be wrong besides the gas/oil possibility or do you need more info?

 

[Fuzzytbay]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

From my description of what the engine is doing, do you have any suggestions as to what may be wrong besides the gas/oil possibility or do you need more info?

I hate to guess, but assumeing it IS a four stroke, I'd almost say old gas in the carb. Its gone to varnish and is now gumming up fuel passages. For a quick check, remove the "fixed" high speed jet cover on the carb. (it should be a brass nut near the bottom) and look at the cover for signs of "gunk". It should look like clean new brass, if it has greenish stuff on it, or smells like varnish, etc then you know the carb needs to be taken apart and cleaned.

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Thanks Fuzzytbay. I'll check that first thing tomorrow and let you know what I find. Would that also cause the high revving with little thrust like something is slipping or is that a totally different issue?

 

[Rudi2]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

When the guy sold me the setup (I bought it at a local marina and the engine came from his friend who works at a well known boat and engine dealership/marina) I took his word that it was a 4-stroke. He said that his mechanic had checked the engine and it was ready to go. Since my trips back and forth were so short (I haven't even used a half tank of gas yet), I just never gave a thought to checking the oil.

I'll get some premix tomorrow and give it a try, if the engine even starts.

My gosh man, call the guy at the marina that sold you the boat! He's the one that knows what you have, have him explain it all to you. Don't be messing around putting premix in it if it's a 4 stroke

 

[will941s]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

This is a two stroke merc 25hp OB....it's a 98' but would be EXACTLY the same as a 03' 2-stroke. If it looks like this then it's a two stroke, different, it's a 4-stroke

 

[will941s]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Pic of the 2-stroke powerhead

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

My gosh man, call the guy at the marina that sold you the boat! He's the one that knows what you have, have him explain it all to you. Don't be messing around putting premix in it if it's a 4 stroke

Actually, I did try to call him but he's away on vacation for the week and the mechanic who was there when I called was not the one who worked on my boat. As for the guy who sold me the motor, I only have his first name and no phone number. That deal was set up through the guy at the local marina who I bought the boat and trailer from. That's why I'm on here asking these questions. To be honest, I didn't want to take this to my local marina (the one where I bought it is on the other side of the river) where everyone knows me and ask, "Uhh, is this a 2-stroke or 4-stroke? Duh." I'd be laughed off the river. :redface:

This is a two stroke merc 25hp OB....it's a 98' but would be EXACTLY the same as a 03' 2-stroke. If it looks like this then it's a two stroke, different, it's a 4-stroke

Pic of the 2-stroke powerhead

Thanks for the pics will941s but now I'm even more confused (if that's possible). My cowl looks different than the one in your pic but the powerhead appears to be the same or pretty dang close if my memory is correct. I'll know for certain tomorrow if that's my powerhead but like I said, that is NOT my cowl. I'll post pics tomorrow.

 

[SC1650]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Does yours look like this one???? This is a 2004 25HP 2 stroke.


http://cgi.ebay.com/ebaymotors/25-h...at_Parts_Accessories_Gear&hash=item3a5be1ff13

 

[lncoop]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

To be honest, I didn't want to take this to my local marina (the one where I bought it is on the other side of the river) where everyone knows me and ask, "Uhh, is this a 2-stroke or 4-stroke? Duh." I'd be laughed off the river. :redface:

You'll be laughed off the river any way if you burn up your outboard as a result of not knowing what you bought. Get over your fear of being laughed at, take it to the nearest shop and ask them to tell you everything they can about the motor just from taking a peek at it. Then you'll quickly find out whether you have 2 or 4 stroke, whether you have oil injection or need to premix, and other goodies that may prevent you from destroying your new to you motor. Only way to learn is to ask. Just do it, man!

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Here are the pics of my Merc. It is apparently a 2-stroke since it pretty much matches the pic that will941s posted of a 2-stroke powerhead even though the cowl isn't quite the same. I'll be having a discussion with the guy that sold me this setup and it's not going to be pretty.

Now that I know that, I'll keep my fingers crossed and hope that I didn't burn it up. I have only used about a half-tank of gas and maybe a total of two hours or less running time spread out over roughly two dozen trips since I put it in the water. I'll get it in the shop as soon as I finish repairing my cabin (that is if the engine runs with oil added to the gas. If not, it'll go in tomorrow).

Can anyone tell me what the proper gas/oil mix is for this - 2003 Mercury Tiller 25hp 2-stroke electric/manual start?

Thanks for all of the help guys. Very much appreciated.

 

[lncoop]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Are you considering running it some more before you put it in the shop? If so, I think you're playing with fire. You're still not sure what kind of motor you have, and even if you're now confident it's a two stroke you don't even know what the fuel/oil ratio should be. You have no way of knowing whether the abuse you may or may not have subjected it to will result in your finding yourself in a potentially dangerous situation such as being stranded down river. Do yourself a favor and go ahead and put it in the shop now, that way they can be looking at it while you're working on your cabin. I'm not trying to be rude, but it just seems like you have a lot of learning to do about your motor before you have any business using it, and if it's at the shop you won't be tempted to run it or tinker with it and cause further, possibly irreparable, damage (if you haven't already). Welcome to iboats. Forgot to say that earlier.

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Are you considering running it some more before you put it in the shop? If so, I think you're playing with fire. You're still not sure what kind of motor you have, and even if you're now confident it's a two stroke you don't even know what the fuel/oil ratio should be. You have no way of knowing whether the abuse you may or may not have subjected it to will result in your finding yourself in a potentially dangerous situation such as being stranded down river. Do yourself a favor and go ahead and put it in the shop now, that way they can be looking at it while you're working on your cabin. I'm not trying to be rude, but it just seems like you have a lot of learning to do about your motor before you have any business using it, and if it's at the shop you won't be tempted to run it or tinker with it and cause further, possibly irreparable, damage (if you haven't already). Welcome to iboats. Forgot to say that earlier.

I appreciate the advice lncoop. I am now confident that this is a 2-stroke but I won't run it until I know for certain what mixture to use. I did just now order the owner's manual and repair manual for this engine. I didn't order before now because of not being sure of what I had. I am mechanically inclined as long as I have a manual or someone guides me through who knows what they're doing. I can take a car engine apart and put it back together without too many extra parts and I can fix just about anything I put my mind to.

Normally, I would take it to the shop after something like this but as I mentioned earlier, the local marina has a wait time of almost three weeks on service repairs right now. I checked with the only other local marina and their wait time isn't much better (I won't take it back where I bought it. I don't trust them now any further than I can spit). I can't work on my cabin which is on an island of the Susquehanna River (I own the island and another, smaller one) without the motor, and I'm not willing to wait three weeks. Vandals had broken in sometime in the last year and destroyed the place including breaking out every window. I have a dock and steps to build, and most of the furnishings need replaced, the deck just got hit a week and a half ago with three large tree branches and there is a hole in the roof. AND I have family and friends, some from out-of-state, expecting to spend the July 4th weekend there!!! This boat and motor are my only transportation over until I find a reasonably priced pontoon.

As for getting stranded, there is ALWAYS someone on the river this time of the year, even at night. I always have a horn, flares, and an anchor (and of course life vests) in the boat as well as a new set of oars that work quite well (I tested them while the river was higher and a bit faster than it is now). In a really tight situation, I also have my cell which works anywhere on the river in my area and, if worse comes to worse, I am a fairly strong swimmer having been raised on those islands - we spent every summer over there, even through a hurricane when I was real young. We would head over as soon as school was out and head back the week before it started again - we spent a lot of time in the water swimming. I may be a bit rusty in my boating skills and my knowledge of today's motors, but I am confident in my abilities in an emergency situation.

But I still need to know the proper mixture for this engine, so if anyone knows what that is, please post it so that I don't have to wait for the manuals to arrive.

And thanks for the welcome lncoop! I'm sure I'll be using iboats quite often from now on.

 

[RicMic]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

If it dosn't have oil injection and without an oil tank, it dosn't the ratio is 50:1or one pint(473ml) to six gallons of gas. The first tank on a new engine Mercury recommends running double oil on two strokes and I am pretty sure running 50:1 for one tank on a four stroke wouldn't hurt anything either, maybe other than a bit of plug fouling, if even that.

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

If it dosn't have oil injection and without an oil tank, it dosn't the ratio is 50:1or one pint(473ml) to six gallons of gas. The first tank on a new engine Mercury recommends running double oil on two strokes and I am pretty sure running 50:1 for one tank on a four stroke wouldn't hurt anything either, maybe other than a bit of plug fouling, if even that.

Thanks for the info RicMic. Even though mine is hardly a new engine, I think that under the circumstances, I'll run a tank with a double mix first, and then go to the 50:1. I'll give it a shot tomorrow and let you all know how it turns out.

Thanks everyone for all of your help. It is VERY much appreciated.

 

[will941s]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Yep....it's a 2-stroke. GREAT MOTOR, I run mine at about 40:1 mixture because I like it a little rich, but manual calls for 50:1. No oil injection on the motor, never had one, don't make one for it. All the merc 25, 2-strokes are premix only. Since you did run it without oil, tilt it up and put some 2-stroke oil in the cylinders through the plug holes, rotate the flywheel over a few times and do it again. Take the box off the front of the carb, hold the throttle open and spray some 2-stroke oil in there also. Let it sit for a day or so then start it. Run it til it reaches full operating temp and do a compression test. 120psi per cylinder is good, 130-135 is great, 90-up is acceptable as long as there is no more than a 15% difference between the two cylinders. Do the test with both plugs removed and the carb fully open. If it checks out......ENJOY THIS WONDERFUL MOTOR!

 

[Adder]

Re: Mercury 25hp - How do I tell whether it is a 2-stroke or 4-stroke?

Thanks again will941s. That info is much appreciated. I had planned on putting some in the cylinders, but never gave the carb a thought nor had I planned on leaving it sit for a day (one more day won't kill me if it means saving my engine). I will indeed do as you suggested. If I can get a decent compression within the 15%, I'll be able to get back and forth to work on the cabin (no pleasure boating nor side trips). As soon as I either get a pontoon or the July 4th weekend is over, I am still planning on getting it into the shop and have them give it a thorough going-over even if everything checks out OK just for my peace of mind.