Hot Rod 25hp 2-stroke Merc Sea-Pro Jet Build

[Positrac]

I spent a ton of time this fall in my little Solar 380 tunnel hull inflatable. My Merc 2-stroke 20hp factory jet has had all the mods done to it that can be to get a bit more power out of it but I'm still left needing a bit more power. This particular Merc shares the same block between the 20hp and 25hp models at 24.4 cubic inch. With the 20hp factory jet it is a 25hp motor and while its rated as a 20hp jet it probably only puts out 18 or so HP after the approximate 30% power loss through the jet. Enough for a light weight rig with two guys and half a moose but its not quite enough to get a whole moose quartered up out of the water.

I recently found a mint 2012 Merc Sea Pro 2-stroke 25hp short shaft prop outboard that the original owner was selling. When I say mint, I mean the paint wasn't even worn off the original prop. It looks like new and the seller had taken very good care of it. These motors are very coveted down in the states for jet builds because they are a 30hp (26.3 cubic inch) Tohatsu motor that was just re-badged for Merc. With the 25hp version a carb restrictor plate was added and the timing set set at 20 degrees not 25. Its an easy way to get a 30hp at the head outboard at no additional expense. The motor in prop form also weighs only 112 pounds too so they are known as being one of if not the lightest 30hp outboards on the market. Perfect for a light weight rig. They are also known to be a very solid motor and the design has not changed since to mid-90's. Tohatsu is the largest outboard manufacturer in the world and they still sell this exact motor in other countries around the world.

So, my plan and the reason for this thread is to build a hot rod 2-stroke 25hp jet outboard with the end goal being able to get a whole moose plus 2 guys and gear out in one trip instead of making two like I have had to do this year. The upgrade to 30hp at the head is easy, I've done one before and gained about 6mph top speed in the first aluminum Jon boat I had that had this exact motor on it with a jet pump.

For this build I'll need to but a jet pump, adapter plate and drive shaft with bearings from Outboard Jets out of California. I'd like to buy the components not the whole kit because a lot of the kit won't be used. If anyone has a contact that can get me a decent deal on the parts I'd love to hear from them. I'll be ordering a rubber/polyurethane jet foot intake out of Russia, stainless impeller and stainless liner also. I run that set-up on my current jet and its been awesome. I've hit hundreds of times this fall with almost no wear to the intake or grates. For comparison, I destroyed an aluminum intake in 2 days in bow season with the low water so the difference between the two is unbelievable.

Other mods would include polishing inside the pump and extending or filling in the bottom of the nozzle where the reverse bucket sits so jet a better spray pattern out the nozzle. It's a mod they have been dong in Russia that seems to help direct the jet force. I've already removed the reverse bucket on my other Merc along with the related shift linkage. I run the motor stripped down in this form with a bungy around the back of the motor running from one side of the transom to the other. I found with the reverse bucket on I'd hit rocks hard enough to kick it in neutral and then all forward propulsion would be gone and I'd be stopped. With the reverse bucket removed and the bungy on it still hits but doesn't jump up too far, and I never have to worry about it slipping in neutral. Forward momentum is never lost and I get through the shallowest spots, some of which are not much more that an inch or two deep over rocks. There are also a few other tricks that can be done to exhaust porting so that gases flow better. They all add up to help get the most jam possible out of a small outboard.

Today is just the start and I'll be updating the thread as I go along. It could take quite some time to get the parts out of Outboard Jets but if everything works out I'll be testing it out in the spring. These small tunnel hull Solar inflatables are getting more common with NR Motors in Prince George importing them out of Russia this last year. I've dealt with Darren Bell on numerous occasions and he has been great to deal with. I also have 3 friends that have now bought new boats off Darren. They are a great option for a guy who doesn't want to have a lot of money tied up in a boat or the issue of storing them for the winter. Just deflate and roll it up then tuck it away. They are also a great way to reach spots that the bigger inboard jets shy away from because of lack of water. The only real issue with them is finding a suitable jet motor can be tough. The 25hp Merc 4-strokes weigh in at 186 pounds so they are a bit heavy. While rated at 25hp at the pump they are 30hp at the head so in all reality the 25hp rating is on the high side after pump loss. They do work well but are heavy for a portable motor. The same goes for the 40/30hp Yamahas. Great motors if you don't want to run real skinny but they are so big they are not real portable at 245 pounds. That's why I like the 2-strokes and in my mind they are the motor to get. Light and bomb proof. Its not like a guy is looking for a motor to troll with, for the most part its running 3/4 throttle or better so the fumes are not an issue and they are really not any louder once running than the 4-strokes...well, maybe a bit...lol. Either way, the moose don't seem to care.

[Moo Snukkle]

Great thread
I’ll be following

[Tommy]

Looking forward to your updates.

I want to make some mods also, have a 25/20 merc 2 stroke on a Solar 480. Can understand about removing the bucket and linkages but what the bungee cord for?

Tommy

[Positrac]

Originally Posted by Tommy

Looking forward to your updates.

I want to make some mods also, have a 25/20 merc 2 stroke on a Solar 480. Can understand about removing the bucket and linkages but what the bungee cord for?

Tommy

I’ve hit rocks a lot. There are sections of the river I run where the intake is hammering rocks steady. I found the motor when it hits hard can pop up so fast it actually locks itself in the upright position. A good buggy across the back prevents that and helps get the pump back in the water fast, thus helping to keep the boat on step and keep forward momentum.

If you have a pre-2005 Merc 25/20 2-stroke you should pull the pump off sometime and check the exhaust port where it meets the pump. The exhaust port on my factory 20hp Merc jet was 2/3rds covered by the pump. I opened it up with a Dremel and the gases flow way better. It has more snap and the leg doesn’t get nearly as hot as it did before.

They are great little motors. Light and and pretty snappy when compared to a converted 4-stroke 25hp at the head jet.

[Albany]

Hi,
Not sure if you could find a stainless impeller or liner for a small pump obj. I have a fair amount of experience with outboard jets and you really only gain benefit over 100hp- and to be honest I’ve never even seen a stainless liner for one. On smaller motors I also found putting in stainless (on 40 and 60 jets) dropped my rpm (and performance). If I were you I would stick to aluminum.

I have runs intake fins and hated them - it gives a rudder effect. I suggest getting flat intake and getting iron aero intake fins - if you like them great, if not you can easily remove them.

Best of luck with the build.

[Positrac]

Originally Posted by Albany

Hi,
Not sure if you could find a stainless impeller or liner for a small pump obj. I have a fair amount of experience with outboard jets and you really only gain benefit over 100hp- and to be honest I’ve never even seen a stainless liner for one. On smaller motors I also found putting in stainless (on 40 and 60 jets) dropped my rpm (and performance). If I were you I would stick to aluminum.

I have runs intake fins and hated them - it gives a rudder effect. I suggest getting flat intake and getting iron aero intake fins - if you like them great, if not you can easily remove them.

Best of luck with the build.

Hey Albany, thanks for your thoughts. There are a lot of guys running outboard jets out there so it’s good to hear from someone else who has some experience with them.

I’ve ran both aluminum and stainless impellers in small outboard jets too. I would say from experience nothing is gained as far as performance using stainless in a small jet. But I haven’t seen a loss either. The real benefit isn’t performance but longevity. I’ve seen an aluminum impeller get eaten up in a few days to the point where a 1/4” is worn off the leading edge, the periphery has a gap and performance was heading way down. On a 5 day moose trip it really sucks to spend time wrenching on your pump.

I’m currently running a stainless liner and impeller in my Merc 20 jet. A factory Merc 20hp 2-stroke jet actually comes with a stainless impeller straight from the factory when new. I haven’t touched either this season and there is very little wear to the point that I haven’t had to shim the impeller. They basically look like new. Running the water I do there are times I’m machine gunning small rocks out the back of the pump. Aluminum just doesn’t stand up to that. The stainless liner was custom machined. I was replacing the old aluminum liners steady at close to $100 each time. The stainless liner was paid for in a season. To date I’ve had zero issues with it. I shim the impeller as close as possible and that doesn’t change. I just serviced the pump and pulled a shim out but it took up all the clearance so the shim had to go back in.

As for intake fins they do help draw water into the pump but they wouldn’t last 5 minutes in the shallow stuff. When they get mashed flat they also put a lot of pressure on the sides of the intake and I’ve seen them cause significant damage to an aluminum intake in the past. I haven’t ran them for years now.

[Positrac]

The biggest issue with this build will be finding a AE pump for the new Merc 25hp Sea Pro. Being a Tohatsu built motor and the fact they have not been imported since 2012 finding a pump locally will be tough if not impossible. Outboard Jets can get me a new one but delivery will be May-June of next year. While I don’t mind waiting and have a motor to use until I get this thing together it might not make for much of an interesting thread…

[Albany]

Interesting the 25 came with stainless. Last outboard jet I bought was a merc 40 factory jet which also came with stainless- I ran it for a year and then swapped for an aluminum and bumped me another 200ish rpm. I generally don’t pump a lot of gravel but I 100% agree that in some rivers aluminum just doesn’t last. I spent 2 days on the kootenay river years back that absolutely destroyed an impeller and liner - the equivalent of a good 5 years of the bow.

In the past I found both iron aero (south calgary) and outlaw marine in red deer really good at tracking down parts for me. About 4 years ago it seemed impossible to get anything and they both came through. I also know two other guys that seem to have a lot of success finding ad hoc parts (used) out of the southern states (I’ll see if I can get the websites). You may also want to put a wanted add on meanchicken- I have been successful getting a lot of random things from guys on there.

Looking forward to the build

[Tommy]

Originally Posted by Positrac

I’ve hit rocks a lot. There are sections of the river I run where the intake is hammering rocks steady. I found the motor when it hits hard can pop up so fast it actually locks itself in the upright position. A good buggy across the back prevents that and helps get the pump back in the water fast, thus helping to keep the boat on step and keep forward momentum.

If you have a pre-2005 Merc 25/20 2-stroke you should pull the pump off sometime and check the exhaust port where it meets the pump. The exhaust port on my factory 20hp Merc jet was 2/3rds covered by the pump. I opened it up with a Dremel and the gases flow way better. It has more snap and the leg doesn’t get nearly as hot as it did before.

They are great little motors. Light and and pretty snappy when compared to a converted 4-stroke 25hp at the head jet.

OK I see now regarding the bungee cord. Good point about the ports I'll take a look. I see on their web site that Jet Wolf has a black rubber intake and a poly white intake, which do you think would take a hit better?
Tommy

[dodgeboy1979]

Originally Posted by Albany

Interesting the 25 came with stainless. Last outboard jet I bought was a merc 40 factory jet which also came with stainless- I ran it for a year and then swapped for an aluminum and bumped me another 200ish rpm. I generally don’t pump a lot of gravel but I 100% agree that in some rivers aluminum just doesn’t last. I spent 2 days on the kootenay river years back that absolutely destroyed an impeller and liner - the equivalent of a good 5 years of the bow.

In the past I found both iron aero (south calgary) and outlaw marine in red deer really good at tracking down parts for me. About 4 years ago it seemed impossible to get anything and they both came through. I also know two other guys that seem to have a lot of success finding ad hoc parts (used) out of the southern states (I’ll see if I can get the websites). You may also want to put a wanted add on meanchicken- I have been successful getting a lot of random things from guys on there.

Looking forward to the build

I second outlaw marine for sourcing parts, they built great boats and know their stuff. I run their landing craft style boats for work and they are bulletproof.

[Positrac]

So, today was my lucky day.

I’ve been dealing with Bernie from Outlaw Eagle Manufacturing the last few days on a pump for my Tohatsu built Merc Sea-Pro. As luck would have it they had a AE-40 pump for a 40hp Tohatsu that has been on the shelf for years collecting dust. My 25hp Tohatsu takes a AE pump. I received all the specs from Outboard Jets and the two pumps and intakes are the same. The AE-40 comes with a 15 tooth drive shaft whereas the AU comes with a 14 tooth drive shaft to mate to the smaller motor. The only other difference was the adapter plates are different.

Bernie made me an offer on the complete pump conversion that I couldn’t resist. Thanks Bernie. He also gave me a stellar price on a new adapter plate and driveshaft assembly from Outboard Jets. The pump conversion is on the way and the adapter plate should be here in a few weeks since they are available from OJ out of California. I’m going to hold off on the driveshaft assembly for now. Once the pump and motor are here I’ll see what can be done to make a driveshaft from the old prop leg driveshaft and the pump driveshaft. There should be something I can do to mate the lower section of pump driveshaft to the upper section of the old prop leg 14 tooth driveshaft. Once I pull the leg apart I’ll know for sure.

Additionally, the pump intakes are the same between my 2003 Merc 2-stroke 20hp factory jet and the Tohatsu pump conversion kit. So I’ll be swapping out my new polyurethane intake and stainless liner for the new ones from the conversion kit. Thats a bunch more clams saved.

Thanks for the tips here on dealing with Outlaw Eagle. Right from dealing with the receptionist to the sales people it was a great experience. It’s always easier to spend money when you are dealing with a company that has good customer service. I suppose getting the deal of the century helps a bit too…lol.

[Positrac]

Originally Posted by Tommy

OK I see now regarding the bungee cord. Good point about the ports I'll take a look. I see on their web site that Jet Wolf has a black rubber intake and a poly white intake, which do you think would take a hit better?
Tommy

The black ones are actually polyurethane but feel much like a stiff rubber. That’s what I have on my 2003 Merc 20hp factory 2-stroke jet. I’ve hit hundreds of times with no significant damage yet. They work great and would be the first mod I do to a new outboard jet.

[Positrac]

I drove down to Edmonton on Monday and picked up my new-used 2012 Merc Sea-Pro 25hp 2-stroke. A friend who lives down that way had picked it up for me and stored it at his place. The guy I bought it off of had said it was like new with very little hours on it and he was not exaggerating. You couldn’t find an almost ten year old motor that had been better taken care of. I’ve been looking for this exact motor for a few years now so to get one in this shape and at a killer price was quite a find.

[Moo Snukkle]

Immaculate and impressive

[Tommy]

Wow that motor looks clean!Good find, it will work great on your boat.

Tommy

[flyon]

Epic find. Now your boat and motor are color coordinated.

[Positrac]

The jet pump kit arrived from Outlaw Eagle. I got really lucky on this find. A new kit is $3,000 and Outboard Jets won’t be shipping any new ones until next May at the earliest. As previously mentioned, Outlaw Eagle had this one on the shelf for years and with Tohatsu 2-stroke motors not being imported into Canada since 2012 their chance of selling it was pretty low. I ended up paying less than a third of what a new kit would cost even with some extras.

Because this kit was for a 40hp Tohatsu and not the 30hp unit I have I’ll have to wait a couple weeks for the new adapter plate to arrive. I’ll also need to decide if I want to modify the drive shaft to fit the 14 spline output on the motor or buy the correct driveshaft. I can use the original prop drive shaft 14 spline end and combine it with the new pump drive shaft and make one out of the two but that would render the prop lower end useless. My best bet would be to sell the prop lower unit and use that money to buy a new pump drive shaft assembly. The only issue with that is Tohatsu 2-stroke motors are rare so it could be very hard to find someone looking for a used prop leg.

[Positrac]

So, fast forward a few months and my 30hp Merc Sea Pro is all together and ready to hit the water. I sold my old set-up and also bought a new Solar 420 Strela Expedition in Green to go with the extra hp of the re-badged Tohatsu.

I ended up ordering in a new AU adapter plate, new driveshaft assembly, Jet Wolfe stainless impeller and polyurethane intake.

The exhaust where the pump and motor mated was restricted quite a bit just like my factory Merc 20hp so I opened the pump casing up as much as possible with a dremel and carbide burr. This should help it get rid of spent gasses and really helped on the Merc.

No pics but I also changed out the carb restrictor plate for a 30hp model and bumped the timing to 25 degrees, the same as the factory 30hp models. That’s the only difference between to 25 and 30. Everything else is the exact same.

[Positrac]

I’ve stripped the reverse bucket off and filled the mounting holes. The impeller is shimmed as close as it can go without rubbing. I also sanded down and painted the pump Merc Black. The pump came Yammy gray so my ocd got the better of me and now it looks factory.

All said and done the motor weighs 124 pounds. So about 62 pounds lighter than the lightest 25hp Merc 4-stroke factory jet. They are both 30hp at the crank shaft motors and after the 30% loss with the pump they will realistically be in the 22hp range. The 420 only weight 40lbs more than my 380 and with the larger bottom and more planing surface they can actually get more weight up on step with the same motor when compared to the 380. I should be able to get two guys, some gear and a whole moose using the gutless method up and on step now. No more second trip which can be a drag when you’re 60km from the truck.

I can’t wait to get out there and see the whole package in action. With any luck I’ll have some pics this fall of the new set-up with some animals in it.

college road diner menu wilmington nc

[Tommy]

Looks great. I am so glad you put pic's up of the exhaust mod, now I see what to do on mine. Didn't get my Jet Wolf intake foot yet, still looking around for one, PM me if you have any leads on one, if you don't mine.

You think on my 25/20 2 stroke 2004 merc I can fool with timing and carb plate as you did to gain a tad more power?

Tommy

[Positrac]

Originally Posted by Tommy

Looks great. I am so glad you put pic's up of the exhaust mod, now I see what to do on mine. Didn't get my Jet Wolf intake foot yet, still looking around for one, PM me if you have any leads on one, if you don't mine.

You think on my 25/20 2 stroke 2004 merc I can fool with timing and carb plate as you did to gain a tad more power?

Tommy

The Merc 25/20hp 2-strokes are pretty much maxed out. Opening up the exhaust port helps a bit. The head is part of the block so there’s not much you can do with them.

The Merc Sea Pro (Tohatsu) 25hp motors are just a de-tuned 30hp motor, that’s why it’s easy to get the extra 5hp and for cheap. N Being a Tohatsu motor it shares nothing with the Merc. I had one 9 years ago and they really scream compared to the Merc 20/25. Nothing wrong with the Merc 25 but the Tohatsu has a larger displacement and the extra 5hp in a motor that weighs the same.

[Positrac]

Merc 4-stroke 30hp at the crank factory jet at 192lbs compared to the Merc Sea Pro (Tohatsu) 30hp at the crank 2-stroke converted jet at 130lbs. 60lbs difference but also way physically bigger.

The 2-stroke can be packed around by one guy but the 4-stroke is a 2 person job. Both use the same pump and intake.

The 4-stroke is a buddy’s that I installed a new uhmw intake for.

Something to think about for someone looking to get a small jet but still keep it portable.

[Tommy]

Yes that's quite the weight difference, which is exactly why I went for a 2 stroke. I like to keep it as light as possible so I don't need to trailer it.

Question, now that you have a white intake foot to compare you think it's the same material as your black one? I am not having any luck finding a poly foot around here at all and Jet Wolf is not a option.

Found a outfit up in Alaska ( Jetech LLC ) that has stock for a brand called " Vezdehod " that is urethane rubber intake foot, also has alum or steel liners to fit. If I ordered only the intake foot from them, I may have to mod it a bit to fit
my stock liner. Shipping I imagine would be costly though.

Tommy

[Positrac]

Originally Posted by Tommy

Yes that's quite the weight difference, which is exactly why I went for a 2 stroke. I like to keep it as light as possible so I don't need to trailer it.

Question, now that you have a white intake foot to compare you think it's the same material as your black one? I am not having any luck finding a poly foot around here at all and Jet Wolf is not a option.

Found a outfit up in Alaska ( Jetech LLC ) that has stock for a brand called " Vezdehod " that is urethane rubber intake foot, also has alum or steel liners to fit. If I ordered only the intake foot from them, I may have to mod it a bit to fit
my stock liner. Shipping I imagine would be costly though.

Tommy

The white intake is UHMW, just like the skid plates on most jet boats. It’s the first one I’ve seen but it’s pretty nice. Looks to be machined out of a solid piece and good quality. It’s a Jet Wolf just like the black poly intake on my 2-stroke.

The first poly intake I had was a Vezdehod. They are great quality and a bit beefier than the Jet Wolf intakes. Mine stood up to hundreds of hits and looked pretty much new when I sold the boat in the late fall. They are also made in Russia so they will get pretty scarce soon. The only issue with the Vezdehod is they don’t have a spigot that fits into the bottom of the pump to line it up like an original intake or a Jet Wolf. Without that spigot they are very hard to line up when installing it and a good hit could push the intake out of alignment causing the impeller to rub on one side of the liner. Vezdehod does sell a liner with a spigot on it like the larger stock liners on bigger models of intakes which fixes that issue but I could never get one. A stock liner does work but again, it’s a pain to install. I’ve had the intake lined up perfectly to the pump so there is minimal clearance between the liner and impeller but then tightened the mounting bolts and it’s pulled slightly to one side so there is a gap on one side and no clearance on the other side.

[Positrac]

27mph WOT with myself, 50 litres of fuel and a bit of gear. Should be good enough to get 2 guys and a bull moose up and going. It runs about 5mph faster than my old 380 Solar with the 20hp factory Merc.

They’re not made for speed though. With a 30hp at the crank 2-stroke weighing 134lbs it has great power to weight. Ran through stuff a week ago that I would have touched before in the 380.

[JD848]

That is one fine looking setup , getting away from others and being in a good hunting area is all what it's about.

Good for you, excellent job . I love hunting rivers and lakes ,did it for 25 years solo.

Little bit more work at times , but the rewards were good.

Cheers JD

[Tommy]

Nice rig, you think the bottom of the 420 makes it's run shallower than the 380? Or just more power on the jet lifts the 420 up higher out of the water.

Tommy

[Positrac]

The bigger bottom with the same weight motor and gear should float higher. It’s also a different designed and the heavy-duty bottom slides over rocks better than the 380 bottom. I did like the built-in trim tabs on the 380.

The key with these boats is to slow down in the shallows. Need to be on step but slower and they seem to form a bit of a wake to help get through short sections that have very little water.

[ehrgeiz]

27mph downstream or upstream?

On my Honda GX390 mud motor setup with the Stryker 420 I was about 16-18km/h upstream into a bit of headwind.

Downstream I was getting 25-28 km/hr.

2 guys w/ gear.

[eric2381]

How’s the unit performing for you so far? Thanks for the write up