# 2-stroke 25HP mercury stalls while accelerating.



## Jay415

Just bought a 1999 2-stroke 25HP ELH Mercury motor. Run pretty good but I think it might need some carb work. I changed the plugs, cleaned the gas filter, and used fresh gas with ethanol treatment and mercury synthetic 2cycle oil, 50:1. Motor starts right up and seems to idle fine. It'll will putt along slowly so so, but once you give it gas to accelerate it want to stall. I have to play with the choke a little to get it to accelerate. Once I get passed that I can adjust throttle from 1/4 throttle to Wide open and back and forth with no problems or bogging. Once I slow to an idle and try to accelerate again it starts bogging. I though maybe the idle was too low so I turned the idle adjustment screw slightly but it sounds like its idling a little too fast and it hasn't helped, still the same bogging when accelerating. Plus now it's slamming into gear harder. The motor was very clean and sitting around for a while. Am I thinking right, that is must be a carb issue? What should I do to remedy this?


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## GYPSY400

Sounds like the high speed jet is plugged.. By pulling the choke, your fooling the carb into giving more fuel by cutting off the air. 
Float level may need adjustment and cleaning too.

On the other hand, you say that after you get past 1/4 throttle it seems ok.. Perhaps the timing is off.. Don't ask me how to link and sync though.. Never had that problem yet!


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## Jay415

I am doing a seafoam treatment hoping it will clean the carb enough to solve the problem. Here's a short video of how it's running. With the hose hooked up with muffs I can put it in gear and rev it no problem. Not sure if the seafoam helped or if it's because the motor isn't under a load. 

[youtube]z7Q1uD6UBYs[/youtube]


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## Buddychrist

I had the same problem with my 115 but it's Efi so I had to replace the high pressure fuel screen and now it runs like a top!

I'm going with the high speed jet on this one. Carb rebuilds are simple and pretty easy if you know what not to do


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## Jay415

Haha can you list the what not to do's?? Lol I am pretty good mechanically so I don't mind attempting it. I need to find a service manual also. The question is do I have all the right tools.


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## Buddychrist

Jay415 said:


> Haha can you list the what not to do's?? Lol I am pretty good mechanically so I don't mind attempting it. I need to find a service manual also. The question is do I have all the right tools.




1. Have a clean desk
2. Have a gallon of Chem dip from your local autozone 
3. Always put your parts in a line and go from left to right as you remove them, that will tell you what part goes next.
4. Buy a can of Silikroil for tight bolts
5. Buy a can of carb cleaner
6. Count the turns exactly when removing the jet pins. You will need to write this down. One is a low jet, the other is a high jet. Go in 1/2 turns down until it bottoms out. Then write down how many turns and remove it completely.

After everything is removed place your carb in the Chem dip carburetor cleaner for 24 hours. This will remove any sediment buildup and clean it up.

Now onto installing new parts.
1. Go from right to left from your removed parts and line up your new parts exactly.
2. Install the new parts in succession until it is complete.
3. Once it is complete Turn your jet pins all the way out and slowly count the turns out. If you mess up its ok just go back down and retry. There might be a 1/4 turn in the end depending on how it's set.

Install the carb and start your engines. Tune in 1/4 increments until it purrs like a kitten.

The Silikroil is worth it's weight in gold. Use it on any bolts that are stubborn. Spray it and let it sit for a few minutes. I recommend spraying all outside bolts with it and let it sit for an hour before starting the rebuild.

I hope this helps


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## Buddychrist

As for the tools it's pretty simple small shop screws, maybe a set of hex keys. Look to see if your carb needs any special tools, most don't but you never know.

The biggest point is a completely clean cleared shop desk that's been wiped down to remove any dirt or dust. Cleanliness is probably the biggest thing on this one.

Microfiber shop towels are really nice also!


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## Jay415

Thanks I think I'll order a carb rebuild kit and give it a try. I have plenty of tools just wasn't sure if I'd need any special testing equipment. I'm sure I won't have any problem.


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## Buddychrist

It wouldn't be a bad idea to pick up a pop off pressure tool 

I use a mighty vac MV8000




If you are just rebuilding and not messing with it just install the same color or size spring that you remove and the pop off tool wouldn't be needed.

The mv8000 is also a vacuum pump so I've used it many times on multiple applications from fuel vacuum testing for air pockets to sucking lube out of the foot of your engine for replacement!

Really handy tool.

When you do the rebuild the kit will have everything you need and instructions for doing the rebuild. But the pump is just friggin handy.


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## Jay415

Cool thanks for the info. I went to crowleymarine.com I now need to figure out the model number for my motor. It's not I'm the sticker. I thought I would just look it up by the year and 25 HP ELH.


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## Buddychrist

There should be a manufacturing sticker on the right side of the motor when you are standing from the rear. It should say your year, cc displacement, and a few numbers.

Also the two bar codes on the side of the engine has numbers. Just write them down also for searching boats.net


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## Jay415

I have to look again when I get home but the sticker your talking about doesn't have a model number. It has the information you said plus serial number. It says 25hp ELH. But I just looked at boats.net. Looks like the 25 hp ELH is possibly 1025311VD. I'll look around the motor to verify. 

https://www.boats.net/parts/search/Merc/Mercury/1999/parts.html


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## Buddychrist

Search for that long # on boats.net


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## Jay415

Yea that's where I found the number, I just want to check on the motor before I order anything. I don't see the carb rebuild kit on boats.net. I found it on crowleymarine.com for $73.

Thanks again!


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## Jay415

I didn't see any bar codes on the engine. Only the sticker on the right that gives serial number, Hp, year, max rpm etc. and under the cover another sticker that gave some specs like timing and idle rpms.


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## Buddychrist

Jay415 said:


> I didn't see any bar codes on the engine. Only the sticker on the right that gives serial number, Hp, year, max rpm etc. and under the cover another sticker that gave some specs like timing and idle rpms.




I'll take some photos tomorrow of my engine where the numbers are located. If you've got the serial number then you can find it pretty easy, I'll copy it and see if I can hunt it down


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## Buddychrist

https://www.boats.net/parts/search/Merc/Mercury/1999/1025311VD/parts.html

That has full diagrams and parts lists for your specific engine. If there's any part on your motor you can get it from there or pull the mercury SKU and see if you can find another place that is cheaper.

I've ordered from boats.net before and they do pretty good service with quick shipping


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## JMichael

Here's a Sierra kit for $11 cheaper. Not sure what brand the one you're looking at is. 
https://www.wholesalemarine.com/p/1395-8237072/Repair+Kit-Carb,+Mercury+-+Mercruiser+1395-8237072.html


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## Jay415

Found it on boats.net. It's #16 on the schematic part number 823707 2 REPAIR KIT for $59. Same as Crowley for $73. I just ordered that and the water pump kit. Might as well change the impeller, who knows how old it is! Same one you listed also JMichael. Thanks for your help guys! I'll update after the rebuild.


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## Buddychrist

Jay415 said:


> Found it on boats.net. It's #16 on the schematic part number 823707 2 REPAIR KIT for $59. Same as Crowley for $73. I just ordered that and the water pump kit. Might as well change the impeller, who knows how old it is! Same one you listed also JMichael. Thanks for your help guys! I'll update after the rebuild.



If you've got any questions durning the rebuild just hop on here and post photos and I'll help you out! It's pretty simple once you get the hang of it!


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## 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.


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## Buddychrist

Jay415 said:


> 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.


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## 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.


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## 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.


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## Jay415

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


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## 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


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## Buddychrist

Jay415 said:


> 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


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## 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


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## Buddychrist

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


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## 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]


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## 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?


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## Jay415

Buddychrist said:


> 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. 



Buddychrist said:


> 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.


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## 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


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## 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


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## 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?


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## 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<


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## Jay415

crazymanme2 said:


> If you turn the choke knob that advances the timing.


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



crazymanme2 said:


> 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?


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## 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


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## Jay415

Ok makes me feel a little better.thx


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## 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


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## Apex Predator

I had a similar issue recently with a 97' Merc 25. After replacing fuel line, bulb, and fuel filter in the engine, the problem persisted. I turned the tank upside down, opened the tank cap vent, and drained some gas into a clear jar. I had half gas and half water! I replaced the tank, and she runs like a swiss watch now.


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## Jay415

WHAT A RELIEF!!!

I was really nervous that I made a bad purchase with this motor. I was getting 90psi compression in each cylinder. I got my service manual in and specs say that compression should be 120psi or better. Well, the big, big mistake I did was buying a compression gauge from Harbor Freight! I read the reviews on it after I bought it #-o It got horrible reviews! I mean bad! not one person claimed it gave an accurate reading! So I stopped by Pep Boys and picked up a new Actron compression gauge and Bam!!! 135psi in each cylinder!!! SO so happy!! I really though I f'd up with this one! Now just waiting for my carb kit to come in and this thing should purr like a kitten!


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## Jay415

I broke down the carburetor to clean it and it really wasn't that dirty. A little bit in the fuel pump and around the main jet but not in the port. I sprayed everything down and through all ports and openings with Gum Out carb and choke cleaner. Just waiting for the kit to come so I can rebuild it. The main jet was really tight in the plug and I slipped with the screw driver, stripping it a little. Should I replace the main jet or will this be ok?

Edit: the main jet is $3 on boats.net. I just ordered a new one and a new plug as well. Why take a chance with something so cheap!?!?


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## Jay415

Ok here's a stupid question. I tried paying attention to every little detail, but I missed this one. (prob due to the gas spilling all over the place when I took the bowl off :lol

Which way does the float go? 1 or 2? Or does it even matter? I'm guessing 1. 

*1*



*2*


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## Buddychrist

#1 that's how it would get a seal on the bowl


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## Buddychrist

Did you let the carb sit overnight in chemdip before rebuilding?


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## Jay415

No just the acetone spray. Even though it didn't look dirty, it looks almost brand new now except for a little green around brass parts. I didn't rebuild it yet. Kit is expected to be here on the 31st.


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## Jay415

What do the bleeder hoses that come from the reed block cover and go into the side of the cylinders do? I noticed the one on the bottom cylinder is wet with oil around it at the cylinder. Not a lot, but the top one is bone dry.


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## Jay415

In the primer chamber after removing the brass plug, there is a spring, then a silver ball, then a split ring and a rubber o-ring. 

How do I get that split ring out? I tried picking it out with an awl. 

Also how do I get the new one in?


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## Buddychrist

That might not need to come out, when you get the kit in you'll have the instructions and it will tell you how to remove it


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## Jay415

I was hoping for instructions but they didn't come with any. The kit came with new red o-ring and split ring along with the spring and silver ball. 

The one still in the carb looks good but I'm just afraid I softened it when I cleaned the carb out with the acetone. I was amazed on how it disintegrated my vinyl gloves. I tried not to get the acetone on it though. 

I posted the question on boats.net mercury forum also.


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## Jay415

Ok I was able to pop it out. Getting the new one in is gonna be a challenge. I'm glad I got it out though. It was all caked up. Def not as clean as it looked. 

Most of the pieces from the carb looked pretty good except for the diaphragm from the fuel pump. Now that I see the new one, the old one is really stretched out.


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## Jay415

Ok carb all rebuilt. I adjusted the carb, timing, throttle linkage, etc. all to factory specs. Runs great! Just have to do a little fine tuning on the idle air mixture. All in all I am very happy and relieved about not making a bad purchase! Thanks for everyone's help! Especially Buddychrist! 

*Before*
[youtube]0RqT_ProdOc[/youtube]

*After (it's a little dark cause I went out when the sun was setting)*
[youtube]scnPOdhRE7E[/youtube]


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## Buddychrist

No problem at all man!

The difference is night and day isn't it? That thing sounds great! I bet your pulling 24-25 mph with it!


How do you have your friction plate set? I'm still working on getting mine set and it seems I've either got it too tight or too loose.


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## Buddychrist

Also just a tip when checking compression on any engine you have it done at full wide open throttle. Sorry I forgot to tell you that when you were checking your compression. 

But man that motor sounds just as good as the one I have if not better!


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## Jay415

By myself I get about 26-27mph as per the gps. The friction plate for steering? I have that right in the middle.

Does this mean the motor is running too rich? It didn't do this prior to rebuild. Prior to rebuild there was just a few drips. I know some is normal. This was under the motor.


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## Buddychrist

Do you have Oil coming out of the carb? 

Or is that from the foot?

If its coming from the exhaust you could have a bad seal that can get worse if it dries out unsealed.


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## Jay415

Mixed not injected. Not sure what you mean by the foot. It appears to be coming out of the thru-hub exhaust by the prop.


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## Buddychrist

Ok that clears it up for me, run a full can of seafoam through the motor and then lower down your idle and high jets just a 1/8th of a turn


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## Buddychrist

Just make sure if you ever get a gray or milky oil residue from the lower unit means a bad seal.

Black oil is normal that's unburnt fuel, seafoam will smoke like hell but it will burn all the carbon from the engine and give you a cleaner burn. Also get your hands on non ethanol premium unleaded, they run 10x better on it. Don't use gas station oil but get some 2 stroke PWC oil from quicksilver, it's got a higher lubrication and runs real smooth on an outboard.


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## Jay415

which is the high jet? the air/mixture screw? that's really the only adjustment beside the idle screw.

I've looked into non-ethanol fuel and the closest place I found is over 1 1/2 hours away. The gas I'm running still has seafoam in it from my first trial. it's a little diluted now though. it's definitely not lower unit oil that I see.


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## Buddychrist

Drop both the air mix and the idle down a tad and see if it helps. Keep the idle clean but just a little lower and keep the top end good but try the PWC oil from Walmart that's made by quicksilver it really helps.

I'm sure there's non ethanol closer, if you PM me your city I can hunt around, the first place I found was an hour away but after I did some phone calls I found the almond oil company.


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## Buddychrist

https://pure-gas.org/extensions/map.html

There's 91 octane near Syracuse NY
The Nice N Easy on Bartell Road in Brewerton, NY (just off of I81).


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## Jay415

Lol, That's a few hours away. I'm on long island in Nassau County. 

I started using mercury 2 cycle synthetic. But I'll try the one you reccomend.


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## Buddychrist

The mercury two cycle is good stuff too! Are you running Premium?

You could try getting a small gallon of sthil premix non ethanol in 50:1 and run it through.


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## Jay415

No I've been using 87 octane


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## Buddychrist

Jay415 said:


> No I've been using 87 octane



You should be running premium, empty out your current tank and run premium with the mercury 2 stroke oil. That should stop any misburning!

You'll get a much hotter and cleaner burn giving you better throttle response and less oil residue through the hub! Give it a shot and tell us how it goes if you get a chance this weekend


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## crazymanme2

I've always ran 87 octane in my 25hp Merc with no problem. :lol:


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## Buddychrist

crazymanme2 said:


> I've always ran 87 octane in my 25hp Merc with no problem. :lol:



What works for one person might not work for another... The manual says 89 octane, I'm running 92 and it does show a difference especially in throttle response...

The reason I say he should run premium is high elevation on a newly built carb if he is having oil through hub he isn't getting a complete burn and a higher octane will help with that.

Look at your elevation on your GPS and tell me what you've got and I'll give you the correct jetting size per service manual


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## crazymanme2

You sure nobody messed with the timing or got out of whack?I used to race these motors & know them inside out.



> The manual says 89 octane, I'm running 92 and it does show a difference especially in throttle response...



It also has to do with your timing. If I want all the speed I can get I will run 93, no ethanol & bump the timing as far as I can go.It will give me another 3-5 mph.I also run a little bigger jets.(never hurts to be a touch on the rich side)

Alot of outboards have oil through hub especially if you idol alot.I even get it on mine sometimes.I'm not saying higher octane won't give you a cleaner burn just he probably has other issues.


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## Buddychrist

crazymanme2 said:


> You sure nobody messed with the timing or got out of whack?I used to race these motors & know them inside out.
> 
> 
> 
> 
> The manual says 89 octane, I'm running 92 and it does show a difference especially in throttle response...
> 
> 
> 
> 
> It also has to do with your timing. If I want all the speed I can get I will run 93, no ethanol & bump the timing as far as I can go.It will give me another 3-5 mph.I also run a little bigger jets.(never hurts to be a touch on the rich side)
> 
> Alot of outboards have oil through hub especially if you idol alot.I even get it on mine sometimes.I'm not saying higher octane won't give you a cleaner burn just he probably has other issues.
Click to expand...



He Just did a carb rebuild and set the timing, and jets getting it back to factory settings. I know they all put oil through the hub at "idle" but it still shouldn't be globs of oil coming out and it got worse after his carb rebuild. Which goes to tell me turning down the jets an 1/8th turn and run higher octane will fix it.

I only run premium non ethanol in all my boats and smaller engines (Especially my Harley). It's not as cost efficient but they do run better, especially my 25hp outboard gets up on plane faster and has no oil coming out of the hub at all. 

He can't get non ethanol without going for a 1 1/2hr drive since he is in New York... Which I recommended earlier but it's a long ride just for some fuel...

So premium is gonna be the best way hands down because at least that way he will get a better burn closer to non ethanol than just regular 87 octane 10% gasohol. 

I say non ethanol premium is worth the drive but then again it's only 30 minutes away from my home and i have a contract with that oil company. 

Too bad they won't let me get a fleet contract to put regular high sulfur diesel in my old dodge instead of the low sulfur highway crap.


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## Jay415

My elevation is sea level. I've been running it on the bay of long island. 
Excessive idle could be the culprit. I idle down a canal for about 10 min to the launch, then idle the motor to flush it for a few minutes. Maybe it's the build up that is dripping out.


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## Buddychrist

Jay415 said:


> My elevation is sea level. I've been running it on the bay of long island.
> Excessive idle could be the culprit. I idle down a canal for about 10 min to the launch, then idle the motor to flush it for a few minutes. Maybe it's the build up that is dripping out.



Turn the idle pin down a hair and give it some premium and see what it does, its just running a little rich and not burning all the fuel.

Also invest in some E3 spark plugs, that will get the spark dead in the center of the cylinder and give you a full burn every time!


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## Jay415

I'll try all that. What are E3 plugs? Is that a brand? I've been using NGK


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## Buddychrist

E3 are triple prong performance plugs that shoot the spark directly into the cylinder helping get a fuller burn 

NGK's are good and that's what I had on my jetski but after I swapped them to E3 it was a nice performance boost and throttle response was greatly increased


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