More help needed on that 25 HP 1989.

http://www.marineengine.com/boat-forum/showthread.php?412328-1989-25HP-Carb-rebuild
Link to last thread for reference.

Compression is 89 each cylinder, spark is a nice strong blue over 1/2".
Carb and fuel pump rebuilt. Reed was broken and wrong gasket was installed.
I got it on the lake Saturday, but it runs really rough. It is sputtering and the more throttle the rougher it gets. It does stay running on its own now.

In my mind the timing must be way off, because the throttle lever must be adjusted so the throttle cam to roller looks like it is at 1/2 throttle. If adjusted where it should be it won't start. This is the way I received it. Manual says to start the timing adjustment at WOT, but there is no way I would get to WOT, nor would it be safe. I did get to about 1/2 throttle, but the more throttle, the more that engine jumps. It is loud too. I was running with the cowling off.
Any suggestions as to where to start next?
Thanks
Jim

Did you go thru the carb link settings per SELOC? Make sure it's still firing on each cylinder by removing one plug wire at a time while running. How did you set the carb mix screws? Should start w/it 1+1/2 turns CCW from slightly fully CW.

I did start with 1 1/2 turns out. (low speed only, high is fixed jet)
It was close to the original.
The settings I am trying to do are starting on page 6-19 of the Seloc manual.

Last time I grabbed a plug wire (on this engine) while it was running, I got a serious jolt right through the wire.
I'll find some heavy gloves and give that a try.

I got a serious jolt right through the wire.

Click to expand...

Old wires could be randomly leaking high voltage. Look at it running in the dark to see if there is a light show dancing around.

Just tripped over your (second) post here, can I give a synopsis and you tell me if I have it correct?

You have rebuilt the carb and fuel pump.

You fixed your issue with the reeds.

After which, you discovered a gasket issue (carb base) - now corrected.

It's still running like crap, but it you advance the throttle a (fair) bit you can keep it running - although it's shaking like a wet dog on a cold day.

Is that about where it stands right now, or did I miss something (I have a couple of ideas, but want to make sure I'm up to speed here)...

Graham,

Yes you have it pretty correct. Throttle was advanced with the throttle lever being adjusted way off.
Otherwise it won't start.

I was thinking sheared flywheel key.
I don't think the previous owner went that far as to pull the flywheel though, but he did confess up to the wrong carb gasket.
Thanks I am all ears.

I really think you have an air leak - as in sucking too much air somewhere (or letting your air/oil/gas out).

A short story - 3 summers back I took my 14'/15 horse rig way way up north, last 200 miles on logging road. Got 20 some miles down the lake, throttled back to beach the boat, heard a "woof" and the motor started running like crap, then stalled. Wouldn't start unless you gave it a fair bit of throttle, and then still shook real bad.

I "figured" I had blown a main seal - seemed to be running on a cylinder and a half at best. I had some tools but not enough to pull the flywheel, and not wanting to do a 4 hour drive back out to (maybe) find what I thought I needed, I fiddled with the carb and the timing until it kinda ran a little ok, and then increase my oil mix to ensure that even if it was running very lean it might get enough oil to prevent damage. If I advanced the throttle (remote) while my buddy pulled over the motor we could get it started - then slam it into gear and get out to do some fishing (ya, great trip).

Anyhow, got it home, pulled the flywheel and yes the upper main seal was shot, but not as bad as I expected. I replaced it then rebuilt the carb/fuel pump (figured could have been a secondary issue and I had a kit laying around). Fired up the motor and it was still running crappy - again would stall at idle, but with a bit of throttle it was (better) but still poor/shaky.

Fixed the timing, which I had fiddled with, but it was still hitching/shaking. At the point I was about ready to take the motor off and mount my 9.9 I noticed a little piece of gasket material in the lower cowl. It had come from the cover on the intake transfer port (a piece from the number 2 cylinder) - so while the main seal (upper) was part of the problem, the intake gasket was the second part of the problem.

I was losing crankcase pressure for my number 1 cylinder out of the upper crank seal and was blowing my air/oil/fuel out of the intake cover for the number 2 cylinder - so I was running on more like 3/4's of cylinder for most of the trip.

So what I'm getting at here is - aside from cracked coils (which are common now on 80-something small Mercs - they are just getting old), I really don't see too many ignition problems with these models.

You have address the carb/fuel pump/reed issues.

I doubt your flywheel key is sheared - try it - put the motor in reverse, block the prop with a piece of wood so it wont turn at all and try turning the flywheel by hand - if the key is sheared it will move a good bit with a quick jolt (but don't think that's the problem).

I really, really think you have either a badly toasted seal or a blown gasket (either under the transfer port cover - intake OR powerhead base gasket).

But if you want to humour me first, try tightening down the powerhead to 10 foot pounds (I believe there is 6 bolts holding the powerhead to the exhaust plate - 3 on each side) - just torque them back down (without a torque wrench - that would be "just tight" then 1/4 turn more).

If that makes a noticeable improvement I would replace the base gasket. If it fixes the problem the powerhead was loose (although it may still need to be timed correctly).

But my vote really is for "too much air" or loss of air/oil/gas mix...

Is the exhaust plugged ??------What oil the the PO use ??

Yes, could be - I just don't think that the ignition, in any respect, is the issue here. Even if the timing was way out to lunch (and you can only adjust it out so bad), that alone wouldn't cause the issues..

Graham,

The 6 power head to exhaust bolts aren't really accessible as far as I can see.
Are they easy to get at if I remove the lower cowl? Or does that mid cover come off easily?

My manual says it is a type "B" power head, and in the disassembly they show a 3.6HP instead of a larger engine.

I did put it in reverse, block the prop and pulled the starter rope. The flywheel will move about 3/4" then back to where it was. Prop doesn't move at all. Is that 3/4" normal or should the flywheel not move at all?

Everything is so clean you could eat off this engine including the intake covers. Nothing is coming out of them, but I can't swear air isn't getting in.

Racerone,

I will ask the PO. I did ride on his boat more than once when it was running well, but I did see him use oil from a non factory container.
Exhaust plugged where, how?
Smokey bubbles were coming off the water and out the back relief ports.

Graham seems to have a solid point from his experience. If it is sucking air from a gasket leak you can find it using WD-40. With the engine running just spray it using the straw nozzle all around the suspect gaskets. If it sucks it into the engine the RPM should increase or even smooth out while the WD is injested. Then you've found the leak.

Recheck your compression with another gauge as 90psi is way to low on that motor.......

Racerone,

You asked about the oil. Response was "No clue" from the PO.
If I pull the intake port covers, can I inspect the cylinder and pistons? What are those for anyway?

Thanks
Jim

The bolts that hold the powerhead to the exhaust "plate" (under the motor) should be accessible from (below) the bottom cowl (like I mean with the cowl in place looking at the bottom of it - think of the motor simple turned upside down).

They are tight right around where the leg goes into the lower cowl - 3 on each side - should be able to get a deep socket on them no problem without moving or removing anything.

And yes, the covers are there to facilitate machining during production - not present on newer models that are using "lost foam" casting. That's both good/bad (having them there) - good because you can get a look inside - bad because they "blow gaskets"

Serial # is 0C173354

Graham,

OK one cover removed and the 6 bolts are there.
I was able to move them all. There is a light oily mess towards the front very clean in the back.
You may be right, or the lower oil seal is bad? Would a bad lower oil seal cause these symptoms?
Should I consider pulling this power head off? (How big of job is this?)

Are the upper and lower seals replaceable without opening up the engine?

Thanks
Jim

You have to split the motor. Here's what the parts look like (with the crankshaft removed. You DON'T have to remove the crank to change the seals.) A new, green top seal is visible on the crank.

Not a hard job.

Jeff

The "oily mess" at the front could be the lower main seal.

To remove the powerhead you simply unhook anything that is attached to the lower cowl - gas line, harness (if equipped), tell tale hose, the kill switch wire, undo the shift shaft, the throttle/shift linkage, then those 6 bolts and she pulls right off (well sorta - often times it's a little stuck to the exhaust housing but a metal paint scraper usually persuades it to let go) - then it comes off as one complete unit.

You will need to replace the base gasket, but it will also let you get a good look at the exhaust plate (see if it's crudded over - if it is it can be cleaned out with a file or whatever will break out the crud (usually minerals)).

It might sound daunting but I regularly pull small powerheads - they don't weight much (I'm thinking the 25 can't go more than 40 or 50 pounds at worst) and once you have done it once or twice you can seriously do it in under 15 minutes.

Once the powerhead is off the lower main seal (crank seal) is pretty easy to get at. There is a "wear sleeve", an o-ring and then the oil seal - All three pieces run about 25 bucks from Merc - the old ones "pick" out and I usually seat the new ones with a "socket" that's just big enough to catch the edge of the seal and guard and with a little tap they seat back in fine (greased up first of course).

I would still inspect the gasket(s) on the intake covers of the transfer ports. If you blew out the bottom of this gasket that mess could be migrating towards the front of the motor giving the impression of a lower seal. (either condition could account for what you are experiencing since either a main seal or a transfer seal would allow you oil/gas/air to be pushed out before it got to the cylinder) - just from experience I find the transfer gaskets fair more often than the lower main seal (uppers are often bad, but the lowers seem to last better - but they do fail and I have changed them)

The covers I'm talking about are about halfway along the block on the starboard side (right side if you are looking at the prop end) - partially obscured by the shift linkage - oh here's a diagram..

Jeff, don't recall having to split the block to get at the lower seal - the bearing yes, but that's (north) of the seal and the wear sleeve which can be picked off the lower crank without splitting the block...

.."Jeff, don't recall having to split the block to get at the lower seal - the bearing yes, but that's (north) of the seal and the wear sleeve which can be picked off the lower crank without splitting the block... "

Correct as usual, Professor! Forgot that this little gem can have its seals pulled that way. All it takes is a few sheet metal screws driven into the seal body, then used to yank the seals out.

Jeff

kimcrwbr1, Yes that is my engine.
Guys yes it looks doable to me. Good late fall project.
If I remove the power head, I may do all the gaskets including the head and exhaust.
Any reason not to?

The manual says the power head can be removed without taking the lower off. Is this wise?
I was thinking it is better to remove the lower end.

Fatzbullet,

I didn't mean to ignore the compression question, and you aren't the first to mention it.
My 76' 70 HP and 73' 65 HP Evinrudes measure approx. 95 psi. Both obviously are electric start.
My 89' 6 HP measures 70 psi (manual start like the 89' 25HP Mercury in question).
In my mind 89 psi is really good for this engine unless OMCs are normally lower compression than Mercurys?

My only other Mercury was a 1971 7.5HP which kicked my but for months as well. Compression was around 70 psi on that one as well.

You can simply pull the power head with the lower unit in place. I do that as a trouble shooting measure sometimes (not often). With the power head off you can use a power drill to turn the crank shaft and make sure the pump/water tube etc is all ok - get "old faithful" out of the exhaust plate if all is ok.

What you see as the "head" is really just a cover (water jacket) - the cylinders are completely within the upper half of the power head. If any bolts are going to be seized in it will be the ones on this cover. So while it certainly wouldn't hurt to change that gasket, unless you have a tap set and are adept at removing frozen bolts I wouldn't try too hard to take them out (most times I have to drill out and re-tap at least one if I have to pull the cover). If it's leaking it could result in hot running or overheat (in extreme cases) - and it gives you a great look at the water channels/opportunity to clean them up nice, but not a deal breaker if it's not leaking and the bolts won't move.

I would replace all the gaskets (o-rings actually - big rectangular things) on the transfer covers (both intake/exhaust) - only run about 2 bucks a piece. The base gasket (power head) if 5 or 6 bucks, ditto the exhaust cover gasket. (you get a good look at the pistons/cylinders with the transfer covers and exhaust cover removed).

The upper and lower crank seals, plus the lower crank wear guard are all about 13 bucks each - do them for sure.

So for 60 or 70 bucks you can do "all" the potential issues - they are getting old and will certainly solve problems before they occur in the future.

Could have added - if you are simply tired of the motor and want to replace, I certainly would take it off your hands - cheap of course...

I know Jeff would gladly make the same offer

The 25 Merc, made anytime after the early/mid 1980's is a great little motor - probably one of the best Merc has ever produced (ok, Yamaha built alot of it, but Merc put it together)....

That motor new had about 120psi ...

Right, and re-ringing it would bring it back to that.

My old and tired Merc 25 was down to about 90 psi before the re-ring job. Performed MUCH better after it.

Jeff

OK, removal underway.
Flywheel is off. Key isn't sheared.
I will update soon, or have more questions.

OK everything is off except the power head itself, now where do I break the seal, above or below the lower cowl?
It looks like above. If below then the tiller handle assy. will be coming too and that doesn't seem good.
Thanks
Jim

Good news, it came off.
Looks like the lower oil seal is leaking, lots of carbon on the exhaust side.

Bad news, went to wash my hands, NO water.
Well is dry. (damn kids and their 20 minute showers) Turned on backup well pump. We have water for now.
Turned dishwasher back on, it is malfunctioning. Looks like the motor will have to wait a little now.