Boating How-To’s - Help with 1995 Mercury 225

Was out last week and was Headed to a fishing spot about 2 miles away. Got there and fished for a bit no problems. Decided to move spots and run about 6 miles away. Cruising at 4,000RPM and about a mile later the RPM's start to drop. I pull back to neutral and the RPM's drop to around 500 and the boat dies. Try to restart it cranks a few times and nothing. This engine has started on the first crank since I've owned it, which is about a month. So I check the 2 stroke oil level and it's fine. Start the boat and it starts right back up. I've had a tight/sticky throttle cable since ive owned the boat, thought maybe that was it. So I go out a few days ago and I'm cruising at 4000RPM and it does the same thing. Restarts fine but the engine is making a lot of noise. Mechanical noise like its out of oil. It's dark so I can't tell if it smoking at idle or not. Check the oil level and it's fine. Restart and it still making the same noise. Now I'm think about calling sea tow. I unhook the oil line connections at the tank and bleed the pressure out. Hook lines back up and restart. It's starts to sound better. So it's running and sounding like normal again and I go to head home. The boat has very little power it won't plane. Stopped and pumped the fuel bulb. It was firm I just made it hard. Boat runs and will get on plane but only hit about. 3000rpm. Get back to the harbor and idle in. At no wake speed I could smell the 2 stroke oil and was happy about that. When the boat was unloaded and wouldn't plane it was def missing. So I'm going to do plugs and wires. What else should I check? And tips?

Is this an EFI motor?
Before spending any money, I would check fuel pressure. Check for good spark on all cylinders.

Is this an EFI motor?
Before spending any money, I would check fuel pressure. Check for good spark on all cylinders.

No it's carbed with electronic ignition. I will check spark tonight and try to get my buddy's pressure gauge.

Hard to check fuel pressure on a carb motor. I would check the spark.
If I were a gambling man I would bet something has clogged the carbs.

Hard to check fuel pressure on a carb motor. I would check the spark.
If I were a gambling man I would bet something has clogged the carbs.

I'll check spark and if that checks out I'll starting tearing down the carbs and cleaning them. Also I just trailed the boat 660 miles round trip. It ran great on my vacation but now having the issues. Maybe trailering back knocked some stuff lose and clogged the filter or carbs.

That sounds very possible, Do you have a remote water separting fuel filter in the boat, If so take it off and inspect its contents, and always replace it with a new on any time you take it off

Do a compression check on the motor.All plugs out.You should see 120psi on all 6.If that's good,look for a fuel problem,then electrical.

well did a compression check tonight and not so great news.

Cylinder 1: 110 psi
Cylinder 2: 105 psi
Cylinder 3: 100 psi
Cylinder 4: 0 psi
Cylinder 5: 110 psi
Cylinder 6: 105 psi

also with the engine running at idle I went around and unplugged each coil separately. Cylinders 1,2,4 had no effect on the idle. So ya tonight wasn't so great. Where do I go from hear? Whats the next step? Fix the 2 decent cylinders that aren't firing right now and run it till it pops? Gonna see if I can grab a bore scope tomorrow and take a peek into cylinder 4 and see if I can see anything. Thanks for all the help guys.

Here's a picture of the plugs

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Forget the scope and pull the head.You should see what the problem is pretty quickly.you may get lucky and have a blown head gasket.

So got a bad piston!

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So I guess it's time to pull the power head!

Yep,you probably have a problem with the carb for that cylinder,but have them all cleaned as part of your repair.You may get by with just a piston and rings,the cylinder doesn't look hurt.

Ya the cylinder is pretty clean. How hard is this job gonna be? Never cracked open a 2-stroke. Done rebuilds on 4-strokes before.

My money is on the bad gas that caused the damage.....

My money is on the bad gas that caused the damage.....

What do you mean? What bad gas? Lol I'm confused. Are you talking about a lean condition?

Could have been a number of things,but that rounded off top of the piston at the exhaust port is textbook detonation damage.Could be bad gas but if the other cylinders are OK it's more likely a problem specific to one carb.Get a factory manual if you think you are up to the job.Nothing really that difficult,but attention to detail and cleanliness are a must.I'd just deal with that specific piston and button it back up.

Could have been a number of things,but that rounded off top of the piston at the exhaust port is textbook detonation damage.Could be bad gas but if the other cylinders are OK it's more likely a problem specific to one carb.Get a factory manual if you think you are up to the job.Nothing really that difficult,but attention to detail and cleanliness are a must.I'd just deal with that specific piston and button it back up.

Ok I get the bad gas comment now, it's only had premium run in it as long as I've have did. So I agree with you about it being a specific carb problem. I have the Selco online manual, looking for a factory manual now. My understanding is pull the power head, split it own and replace what I need to. And give it all a through cleaning to hopefully remove any remains bits of piston. And of course clean/rebuild all carbs.

Check your email.

Check your email.

Got your email, just replied to it. Thanks again!

if you do the job yourself, take photos as you go to see what it takes for a DIYer to do.

Not reall sure about 2stroke outboards, but a piston replacement on a 4stroke engine could be done with engine in place.

I've done a v8 with new rings and cylinder hone with the engine in the car.

on this I'd take off the carbs and front clam shell and see if the piston could not be removed with the engine still mounted.

What say the rest of you?

My plan is to replace the piston with the power head still attached. Hopefully I can get to the lower bolt needed to gain access to the crank. That would be the only thing stopping me from doing it with the power head attached. I will try to grab pictures. Hopefully get it done this week, if not then this weekend.

My plan is to replace the piston with the power head still attached. Hopefully I can get to the lower bolt needed to gain access to the crank. That would be the only thing stopping me from doing it with the power head attached. I will try to grab pictures. Hopefully get it done this week, if not then this weekend.

I did replace 3 pistons on my 135 mariner v6 with power head on,so i tink you can do the same on the 225 merc.....

Got the piston out no problem. Just has to take off the reed block. Where's the best place online to order engine parts? And THT vendors sell engine parts?

None better for service than Andy at Shipyard Island Marine (THT Vendor).

http://www.thehulltruth.com/shipyard-isl-marine-engine-parts-22/

None better for service than Andy at Shipyard Island Marine (THT Vendor).

http://www.thehulltruth.com/shipyard-isl-marine-engine-parts-22/

They seem to only sell Yamaha and Volvo parts. Any other THT vendors that carry mercury parts?

Mud Runner, thank you again for the service manual. It has been a huge help and I am ever grateful.

They seem to only sell Yamaha and Volvo parts. Any other THT vendors that carry mercury parts?

Mud Runner, thank you again for the service manual. It has been a huge help and I am ever grateful.

You're welcome. Just glad I could help. :thumbsup:

Thanks for all the info Frayed Knot. Looking forward to your progress, as I seem to be having similar problems with my 225 carbed Merc.

Mud Runner, any chance I could have a look-see at that manual? I've been searching everywhere, but without knowing serial numbers (decal is worn out), I'm still not entirely sure what motor I have.

Almost got everything done today! But they sent the wrong intake/reed block gasket. Got the new piston in. I official hate needle bearings lol. So got the piston in and everything bolted back up. Cleaned the carbs and went to mount the reed block back up and discovered the gasket issue. Hopefully I can find the gasket locally tomorrow and get it finished up and fire it up.

SonRise05 PM me your email address and I will email you the manual. Mud Runner was kind enough to email it to so I'll pass it on!

SonRise05 PM me your email address and I will email you the manual. Mud Runner was kind enough to email it to so I'll pass it on!

Thanks a lot. I'm away and won't be able to access the files. :thumbsup:

PM sent...thanks!

ok still having issues. Good news is the cylinder with the new piston seems to be doing just fine. But I have not load tested the engine yet. So got it all finished yesterday and fired it up. Still had a big miss at idle. Started unplugging coil packs to see what cylinders. So its missing on 3 cylinders. I checked all the carbs yesterday and could see them all spraying fuel. Then check spark real quick and every cylinder seemed to have spark. Tested the coil packs tonight following the shop manual and they all tested out ok. Could it be a lean issue at idle on those 3 cylinders? Should I adjust the idle settings on those carbs? Could it be the reed blocks of those 3 cylinders? Anyway to test to see is fuel is getting into the cylinder? I know I have fuel coming out of the carbs jets and I pretty damn sure I have spark. I will swap some coils around in the morning to see what I come up with. Any other ideas?

Check the timing and make sure it is correct. That bank or coil could be firing early which could explain the damaged piston.

Looking more and more like bad.

it is like a soap opera you have me hook now...

A_Frayed_Knot,
Have you done a link and sync on the carbs. Adjusting the idle won't help if the carb throttle plates aren't opening at the same rate. Look in the manual for the link and sync and then adjust idle if needed. It's in section 2 page 5.

Been on vacation for the a bit. Anyways had the engine idling for maybe a total of 45mins working on the cylinders still not working. And heard a clank clank clank. Rings on the replaced piston broke. Not quite sure what I am going to do now. The boat will eventaully be fully restored and have twin 125's on the back. So trying to figure out if I want to spend more money to get it running for the rest of the season.

Been on vacation for the a bit. Anyways had the engine idling for maybe a total of 45mins working on the cylinders still not working. And heard a clank clank clank. Rings on the replaced piston broke. Not quite sure what I am going to do now. The boat will eventaully be fully restored and have twin 125's on the back. So trying to figure out if I want to spend more money to get it running for the rest of the season.

now I bet the cylinder walls are all scored up now.

I feel for you.

Why did the rings break? I'm guessing too little end gap,did you check it? Possibly hooked on a port?Ring ridge in the cylinder? Point being,if you missed a step in the setup,you could address the cause of the ring breakage and save the season.

Why did the rings break? I'm guessing too little end gap,did you check it? Possibly hooked on a port?Ring ridge in the cylinder? Point being,if you missed a step in the setup,you could address the cause of the ring breakage and save the season.

isn't there some kind of "keeper" that keeps these 2stroke rings in a certain orientation so the gaps don't find themselves at the port?

I'm not sure how that is done. If there is such a thing, he might have missed that step.

isn't there some kind of "keeper" that keeps these 2stroke rings in a certain orientation so the gaps don't find themselves at the port?

I'm not sure how that is done. If there is such a thing, he might have missed that step.

The pistons have locating pins in the ring groove that keep the rings from rotating in the groove.The rings usually need to be installed with a certain side up.If a ring hooks in a port,the problem can be the ring end gap is too tight and the ring ends touch or the port not being radiused after boring.

the ring were facing the proper direction and positioned in the locating pins. At least they were right up to the point of putting it into the cylinder. My best guess is that when honing the cylinder I damaged either the intake or exhaust port radius and that caused the ring to fail. I have not touched the engine since I pulled the head of and saw the broken ring. So I do not know what caused the failure. And I still have the issue of the other cylinders not running properly still.

Crap I feel for you...not a fun thing to see after fixing the thing yourself trying to save money.

Well finally some good news, but first the bad. So i had replaced the piston and rings and it failed shortly after the first startup. I went on vacation and gave up on it for a bit. Last week I finally tore it down for the second time to find the cause of the second failure. Well it turns out it was my fair. At some point during the first install a roller bearing dropped out of the crankshaft cage bearing. It landed in the intake port. And ended up making contact with the piston and then destroying the piston.

So I fixed that port and ordered some new parts. It's currently running good. Spent about and hour idling in the driveway then took her out in the water for about 45 minutes. It was really nice to be back on the water!

Thank you all for all your help and tips!

Well finally some good news, but first the bad. So i had replaced the piston and rings and it failed shortly after the first startup. I went on vacation and gave up on it for a bit. Last week I finally tore it down for the second time to find the cause of the second failure. Well it turns out it was my fair. At some point during the first install a roller bearing dropped out of the crankshaft cage bearing. It landed in the intake port. And ended up making contact with the piston and then destroying the piston.

So I fixed that port and ordered some new parts. It's currently running good. Spent about and hour idling in the driveway then took her out in the water for about 45 minutes. It was really nice to be back on the water!

Thank you all for all your help and tips!

I'm glad you were able to find the cause and fix it. .

I feel your pain.... ive rebuilt many 2stroke race motors for mx only to have them fail .... sometimes due to mechanic (me) error. You live and you learn. One time I put the same piston on backwards twice with the rings facing the wrong direction.

A friend of mine had the same motor. It ran of 5 cylinders for a whole season. Its now back on 6 and running perfectly