2-stroke 25HP mercury stalls while accelerating.

[Jay415]

Thanks I appreciate it!! I'm looking for a service manual. Have you ever heard of or used this site? Is it legit?
https://www.instant-manual.com/1965-2004_Mercury-Mariner_Outboard_Service_Manuals.html

Selecting the one I would need brought me here
https://www.tradebit.com/filedetail.php/169757182-1990-2000-mercury-mariner-service-manual-2

The manual descriptions on eBay are vague so I don't know which one, if any are correct.

 

[Buddychrist]

Thanks I appreciate it!! I'm looking for a service manual. Have you ever heard of or used this site? Is it legit?
https://www.instant-manual.com/1965-2004_Mercury-Mariner_Outboard_Service_Manuals.html

Selecting the one I would need brought me here
https://www.tradebit.com/filedetail.php/169757182-1990-2000-mercury-mariner-service-manual-2

The manual descriptions on eBay are vague so I don't know which one, if any are correct.

I would recommend contacting a local marina and seeing if they have a regular service manual instead of buying one offline because in the end you'll want it on paper anyways.

Mercury might sell the manuals directly if you contact them. I own factory service manuals for everything I own with an engine. Any off brand manual isn't the same as much as they claim it is.

You should get straight forward instructions with the rebuild kit though. I'd wait for those in the package. Order a full one from mercury directly whenever you've filled up your change jar. Not necessity but it's jam up nice to have.

 

[Jay415]

Yea I definitely want the service manual. I like to have as much info as possible. Here's where I'm confused. This one for example, is this the one I want?
https://pages.ebay.com/link/?nav=item.view&id=200793271927
I just don't like that some manuals say "blabla and up" I don't understand why it's not a range.

 

[Buddychrist]

Pull up the service manual part number from mercury and reference it to your engines serial #. That will tell you if it's the right one.

 

[Jay415]

Ok thanks! I feel like I know nothing! I promise I'm not that dumb! Lol

 

[Buddychrist]

https://www.boats.net/parts/search/Merc/Mercury/1999/1025311VD/Service-Support Material/parts.html

There's a service manual from boats.net that references your engine. Just pull the number from there and check if the eBay post matches

 

[Buddychrist]

Ok thanks! I feel like I know nothing! I promise I'm not that dumb! Lol

Hey man I don't judge at all, my dad can't find anything if you hand him a keyboard but if you give him tools it's like chuck norris himself would tip his hat

 

[Jay415]

I ordered a service manual off eBay last night. It wasn't the one I originally thought. I used your suggestion and went to boats.net to get the part number. Not sure if it's OEM but it looks like it.

https://pages.ebay.com/link/?nav=item.view&id=200699032903

 

[Buddychrist]

It's OEM and a great price man!!!

 

[Jay415]

Ok cool!

I went out today. Here's a good example of what the motor does. You can't hear it in the video, but I noticed today, it sounds like it knocks at idle speeds and just above idle speed. Wide open no knock. At the end of the video after slowing down completely it bogs again when accelerating.
[youtube]0RqT_ProdOc[/youtube]

 

[Buddychrist]

Did you try opening the cap on your gas tank? How old is the gas tank and the fuel lines?

As an old jet ski tuning trick you can tie off your boat to a dock with a few ropes and carefully with the cowl off of the engine adjust your low speed jet.

As for your high speed jet have you tried opening it up considering it is starving for fuel? I still go with the rebuild 100% but for the time being you can adjust the jets and see if it runs any better?

 

[Jay415]

Did you try opening the cap on your gas tank? How old is the gas tank and the fuel lines?

I haven't opened the gas cap but the vent on the cap is wide open. Gas tank and line from tank to motor is brand new. Lines in the motor, who knows, might be original. Gas is fresh from last week.

As an old jet ski tuning trick you can tie off your boat to a dock with a few ropes and carefully with the cowl off of the engine adjust your low speed jet.

As for your high speed jet have you tried opening it up considering it is starving for fuel? I still go with the rebuild 100% but for the time being you can adjust the jets and see if it runs any better?

Which is the high speed jet and which is the low speed jet? And is one of them what I tried adjusting through the hole in the air filter? Had to remove a black cap in air filter to access it. I read somewhere that factory specs is one and a half turns after lightly bottoming out screw. Mine was and 2 turns and 1 1/2 turns would stall motor.

 

[Buddychrist]

I don't know for your year of engine, it will definitely tell you on the service manual when you get it in the mail

 

[Jay415]

I think my description of pulling the choke has been inaccurate. I think the choke is controlled by the motor. The knob itself says "pull to prime". When you pull the knob it depresses a little blue plunger on the side of the carburetor. When the engine is off, pulling the knob sounds like it is forcing gas into the carberator. It reminds me of pressing the primer bulb on a lawnmower carberator. Not sure exactly how it works.

Can't wait til I get this manual!! Lol

 

[Jay415]

Ok did some more diagnostics. Looks like this is going to be a big learning experience for me. Checked compression again and got 100psi in each cylinder cold. Engine warmed up it drops to 90psi. Both cylinders are the same though. Sound like a blown head gasket? What else would cause low compression but both cylinders the same?

 

[crazymanme2]

That year motor has a primer not a choke as they call it.As you already stated it just shoots a bit of gas in the carb.If you turn the choke knob that advances the timing.
That motor should have 125# or better for compression.Put some 2 stroke oil in the cylinders & see what your compression is than.If it's up than you have bad rings or other problems. [-o<

 

[Jay415]

If you turn the choke knob that advances the timing.

Where is the choke knob? Are you talking about the primer knob?

That motor should have 125# or better for compression.Put some 2 stroke oil in the cylinders & see what your compression is than.If it's up than you have bad rings or other problems. [-o<

How much oil?
Does it matter cold or warmed up?
What if the pressure doesn't go up?


The cylinders stay consistent with each other warmed up and cold. I'm just guessing but I was thinking that it had to be something that was affecting both cylinders. Like the head gasket. What do you think?

 

[Buddychrist]

The 25hp mercury 2 stroke has a Tohatsu engine and they come from the factory at ~90lbs that's just the nature of the beast from around our year of motor.

As long as you have 80-90psi or better with no more 10% deviation on compression of each cylinder and considering you are getting matching #'s you are fine

 

[Jay415]

Ok makes me feel a little better.thx

 

[Buddychrist]

No problem buddy

There's a lot of differences in mercury like our 25hp's have Tohatsu engines yet my 115hp mercury has a Yamaha engine.

If you ever need me to walk you through something just shoot me a pm and I'll send you my number