1995 Mercury 25hp 2 stroke issues

[HookMeUpII]

I am new to the forum. I have a 1995 Mercury 25hp 0G157267. The motor is in great shape for it's age. It's used mostly for duck hunting here in NJ from October-January. Being an older motor, I went through a bunch of items: new water pump, carb rebuild with OEM parts, new fuel lines/filter/primer/connectors and tank, new spark plugs, cylinder head water jacket gasket (was leaking), new thermostat, and all the normal maintenance items like lower unit oil. Everything was done exactly

The motor starts no problem, idles, and runs WOT. Lately though, after idling for a while (setting decoys) when I go up to go on plane it sometimes sputters and dies. Once it clears itself out it runs great again. Flushing it with muffs yesterday, I revved it briefly and when it came back to idle it died again. I checked the compression, 125 psi both cylinders. I pulled the plugs which are attached below.

I do believe I have a defective t-stat as it seems like it may be partially stuck open. Plenty of water out the tell tale but the t-stat doesn't seem like it ever closes off to maintain operating temp. Maybe running too cold causing a rich condition?

Could this be a reed valve issue?

 

[airshot]

I would try going one heat range hotter on the plugs, all your idling doesnt help the plugs stay clean. I have had my best sucess with NGK plugs...for what that is worth

 

[racerone]

Do a spark intensity test.----Does spark jump a gap of 3/8" on both leads , yes or no ?

 

[HookMeUpII]

I would try going one heat range hotter on the plugs, all your idling doesnt help the plugs stay clean. I have had my best sucess with NGK plugs...for what that is worth

I'm using the stock NGK plugs at the moment. I don't know that I want to go one hotter because if anything it's just masking another issue.

Do a spark intensity test.----Does spark jump a gap of 3/8" on both leads , yes or no ?

I will do that test and report back.

 

[Faztbullet]

Make sure the recirc lines are not restricted as this will puddle fuel in front of reed and cause lower plug to foul

 

[HookMeUpII]

Update: Put fresh plugs with proper gap in. Checked plug wire connections. Also put a new t-stat in because the other seemed potentially defective. Still having the same issue: Bogs and stumbles accelerating after idling for a while. After running WOT it's fine and accelerates well but if it idles for a bit, issue arises again.

Make sure the recirc lines are not restricted as this will puddle fuel in front of reed and cause lower plug to foul

Well you may be onto something. Could either be that or bad reeds. Last night doing the plugs I noticed some fuel in the throat of the carb and also running down into the cowling from what I believe to be, the throat of the carb as well. Pic for reference. Fuel residue can be seen in carb throat.

More than likely a new set of Boyesen reeds should be next? Since those lines are on the reed plate I supoose I will check them as well.

 

[flyingscott]

What is your compression? Clean your carb and get a OEM carb kit that includes the primer and fuel pump gaskets. Then make sure the ball and spring are in good condition. Unless the reed valve is broke no need to replace them. And if you have one broke you will have bigger issues

 

[HookMeUpII]

What is your compression? Clean your carb and get a OEM carb kit that includes the primer and fuel pump gaskets. Then make sure the ball and spring are in good condition. Unless the reed valve is broke no need to replace them. And if you have one broke you will have bigger issues

With all due respect, in my initial post I put compression figures. 125 psi on both cylinders and that wasn't with the WOT even that the factory service manual suggests which should push it higher. Carb was completely rebuilt with OEM parts (not cheap), per the factory manual. Float setting, torque specs (even the screws; I have all the tools and wrenches), etc. New filter, fuel lines, primer bulb, factory fuel connectors, t-stat, water pump, etc.

At this point I am thinking it's either reeds not closing properly and possibly (but not likely) spark. The motor runs like a champ once it clears itself out. WOT, cruise, etc. Just bogs and coughs accelerating to plane after idling for a while. If I go right back up on plane after coming off, no problems at all. That leads me to believe it's not spark. I may grease the spark advance linkage because it seems like if it sticks, that can cause an issue too.

I am waiting on the gaskets for the reed block and a carb base gasket since that needs to come off. Reeds seem like cheap insurance on an almost 30 year old motor for $38.

 

[flyingscott]

Well with all due respect good luck with your motor you seem to have all the answers.

 

[nola mike]

Have you checked the timing?

 

[HookMeUpII]

Well with all due respect good luck with your motor you seem to have all the answers.

No need for a tongue in cheek comment. I appreciate the input but as I stated, these are all brand-new parts to the tune of near $200. The carb rebuild kit (with fuel diaphragm gaskets, new primer ball and spring, etc.) was not cheap. That alone was $150 with shipping. At this point, I imagine it is likely something else being I used all OEM parts and rebuilt everything to the specs in the service manual.

 

[HookMeUpII]

Have you checked the timing?

I have not but (lucky me) this is the electronic spark advance model. I will start with greasing the little linkage first. I have read some of the manual on how to check the timing but it seems like there is minimal adjustment that can be done. It seems like the CDI box controls most of it. With that being said, if you can offer any insight to that it would be greatly appreciated. I am pretty comfortable with the manual "link sync" process but this e-advance system confuses me a little. It seems there is set-up timing that can't be changed, WOT throttle timing can't be changed, but apparently there is a component that can be changed?

 

[James R]

It may be something as simple as fuel delivery. For example try leaning it out. Could be the choke is leaking. The primer could also be leaking. It does sound like excess fuel is clogging up the works as has been referenced with the recirculation lines. I admit I am a bit rusty on this model but memory serves reasonably well.

 

[nola mike]

I have not but (lucky me) this is the electronic spark advance model. I will start with greasing the little linkage first. I have read some of the manual on how to check the timing but it seems like there is minimal adjustment that can be done. It seems like the CDI box controls most of it. With that being said, if you can offer any insight to that it would be greatly appreciated. I am pretty comfortable with the manual "link sync" process but this e-advance system confuses me a little. It seems there is set-up timing that can't be changed, WOT throttle timing can't be changed, but apparently there is a component that can be changed?

I've got the mechanical advance on mine (interesting that the newer models are mechanical) so haven't seen the electronic in person. It appears that only the set up timing is adjustable, which is not idle timing. The setup is 28' BTDC @3K rpm, and idle is 4'+/- 2' @ 750 rpm. Probably not going to be an issue unless it's messed with, but worth checking.

 

[nola mike]

It does sound like excess fuel is clogging up the works as has been referenced with the recirculation lines. I admit I am a bit rusty on this model but memory serves reasonably well.

Could you explain the recirculation lines? Not familiar with what these are...

 

[flyingscott]

No need for a tongue in cheek comment. I appreciate the input but as I stated, these are all brand-new parts to the tune of near $200. The carb rebuild kit (with fuel diaphragm gaskets, new primer ball and spring, etc.) was not cheap. That alone was $150 with shipping. At this point, I imagine it is likely something else being I used all OEM parts and rebuilt everything to the specs in the service manual.

Did you adjust the low speed screw? What about the carb sync? What is your float height? Not abnormal for a 2 strk to load up a little at an idle.

 

[Prop head]

I am new to the forum. I have a 1995 Mercury 25hp 0G157267. The motor is in great shape for it's age. It's used mostly for duck hunting here in NJ from October-January. Being an older motor, I went through a bunch of items: new water pump, carb rebuild with OEM parts, new fuel lines/filter/primer/connectors and tank, new spark plugs, cylinder head water jacket gasket (was leaking), new thermostat, and all the normal maintenance items like lower unit oil. Everything was done exactly

The motor starts no problem, idles, and runs WOT. Lately though, after idling for a while (setting decoys) when I go up to go on plane it sometimes sputters and dies. Once it clears itself out it runs great again. Flushing it with muffs yesterday, I revved it briefly and when it came back to idle it died again. I checked the compression, 125 psi both cylinders. I pulled the plugs which are attached below.

I do believe I have a defective t-stat as it seems like it may be partially stuck open. Plenty of water out the tell tale but the t-stat doesn't seem like it ever closes off to maintain operating temp. Maybe running too cold causing a rich condition?

Could this be

I am new to the forum. I have a 1995 Mercury 25hp 0G157267. The motor is in great shape for it's age. It's used mostly for duck hunting here in NJ from October-January. Being an older motor, I went through a bunch of items: new water pump, carb rebuild with OEM parts, new fuel lines/filter/primer/connectors and tank, new spark plugs, cylinder head water jacket gasket (was leaking), new thermostat, and all the normal maintenance items like lower unit oil. Everything was done exactly

The motor starts no problem, idles, and runs WOT. Lately though, after idling for a while (setting decoys) when I go up to go on plane it sometimes sputters and dies. Once it clears itself out it runs great again. Flushing it with muffs yesterday, I revved it briefly and when it came back to idle it died again. I checked the compression, 125 psi both cylinders. I pulled the plugs which are attached below.

I do believe I have a defective t-stat as it seems like it may be partially stuck open. Plenty of water out the tell tale but the t-stat doesn't seem like it ever closes off to maintain operating temp. Maybe running too cold causing a rich condition?

Could this be a reed valve issue?View attachment 374093View attachment 374094View attachment 374095

Here is my thoughts. I would check your coils. As they heat up they can be prone to intermittent failure as they get older. If your reed valves were bad you would not have 125 on the compression test. Engine temp should be almost hot to the touch around the plugs and warm water should be coming out of the telltale. Good call replacing the t-stat. Also check for air leaks in the fuel system. Good luck!!!

 

[airshot]

I'm using the stock NGK plugs at the moment. I don't know that I want to go one hotter because if anything it's just masking another issue

Not really, most two strokes will start to load up after long periods of idle, just there nature...this is why folks that troll use a small kicker motor, to keep the big motor from loading up!! Most mfgrs will recomend going one range hotter for long periods of idle !! Your plugs are wet, typical of long periods of idle... You said the motor runs great, only issues are after long periods of idle !!!