Ran across this video a few days ago after picking up a non running 2.5hp mercury. Was told that a shop cleaned the carb but recommended replacing due to in being pretty gummed up. Also had to plastic weld the neck of the fuel tank. I found the part number for the carb had been superseded a couple of times and not available. Ordered a 32 dollar carb off amazon that was for a 3.5, 4 and 5hp model. Outward appearance was the same but after removing the old carb, I noticed the throttle plate and bore to be much smaller than the replacement. Engine runs great with no way to compare with the original since It was non running when I got it.
I bought a 2.5 long shaft to replace my 3.5 short shaft because it was too short and then just disassembled my 3.5 to keep for parts and placed it all in a bin. I took the 3.5's carb and swapped out the brand new 2.5 carb. It was definitely different and i picked up about 1/2 to 1mph on the pond prowler in the ocean. That range was dependent on headwind, swell and current. I plan on taking out the high speed jet and drilling it out a little bit at a time and then running each mod and checking the soark plug after each hour run to make sure i find the perfect ratio before it gets too rich. I aaked the people that sell the 5hp upgrade carn about why its 5hp and all i got was "Duhhhhhhh.... We dont know..." Yeah right. Anyway, it has to be the jets. All of the specs and bores are the same on their 5hp carb compared to the 3.5 carb. Stay tuned.
My 2.5 is pretty slow I wanted a bigger motor but found a 3.5 cheap in good working order. Its not much of an upgrade but at least I will get out of the canals a little quicker on my12ft sea nymph. This video made me glad I got it. I saved 1K over the new 4hp . Its a 2009 4 stroke low hours got it for 300
Great video. I have a 3.5 I’ll be putting on my 12’ tinny this summer. I’ve seen them plane here on RUclips with an adult. So if it’s the difference between planing or not, for me the $300 is worth it. I also got a metal prop for mine.
I've been waiting for a video on this subject for years!!!! (MY Mercury 2.5HP to 3.5HP conversion.) I have a question maybe you might help with. I have the Mercury 2.5 HP four stroke outboard and I was wondering if it would be up-gradable to 3.5 HP by merely changing the Carb Jets. You stated that the difference in the two was the carb.. But check this out... My basis for this theory arose when I was looking for parts online for the motor. (I bought the motor new from Academy back in (2013) It's a 2010. got figure... anyway. As I was looking through the parts diagrams for the 2.5 HP and the 3.2 HP I noticed that ALL the engine parts are the same IE, SAME PART #s… The cylinders are the same size, the bore is the same, the stroke distances are the same. The ONLY differences I could find ANYWHERE were Main jets and Slow jets. They had different part #s. The part number for The Carb Housings are different too... BUT EVERYTHING ELSE IS THE SAME. So in my “Genius”, I figured that if I were to replace the 2.5 HP’s jets with jets meant for the 3.5 HP, the power should increase. "Larger jet(s) more fuel flow". Now I’ve already bought the jets (but not installed them yet) and I was thinking that the jet holes on the 3.5’s will be a little bit larger, letting in more fuel… and thus producing more power at the throttle. I don't have a tachometer... So- I’m thinking the simplest, quickest way to see if this works would be to run the motor in its original state and record the High and Low speed sounds from a certain distance… Then change out the jets and record the High and Low speed sounds of the motor again. Then compare the before and after sounds to see if there is in fact a difference. I know this is a cave man approach to a comparison but again I don't have a tach. I might do a speed test on the water test, who knows... anyway. Does this Rational make since to you? Thanks.
I have not taken the carbs off and measured, but I would assume we are able to flow more air through the throat of the carb. This would then allow more fuel and higher rpm. Just adding more fuel should have a negative effect on top end performance. As for recording sound and comparing...perhaps you may hear a difference...but if we are flowing more air and fuel, it will sound different anyway. If you were able to modify the air flow. On the larger engines, air flow is restricted with a grommet. So they can use a single intake version across all the engines.
@@TheMarineDoctor Yeah when I saw that the carb had a different part #, I hoped the air intake was not too different to work... I've noticed that I hit top end (max rpm) way before I run out of throttle at the tiller, about half way... Kinda weird... Out of curiosity, I ordered and picked up the 3.5hp version of the main jet and slow jets sometime ago. I'll try to come back and let you know what the results are. As I said before your video was the only one that I've been able to find that even touched on this subject. Thanks.
So the difference between the 2.5 and the 3.5 is the carb. So rather than just buying jetting, one could theoretically upgrade by buying the carb. Ok, so the upgrade I see a lot of folks making on the 3.5 is the 5hp prop and carb combo. Being the only difference between the 2.5 and the 3.5 is the carb, could the 5hp conversion kit be theoretically installed on the 2.5?
I ordered the 3.5 to 5hp upgrade kit. My suspicion is that it's a larger throat carb that's meant to mimic the performance of a 5hp on the 3.5hp base. If it doesn't work I'll be out a couple of bucks but filled with knowledge.
There are a few folks on RUclips who have tried and indicated that the 3.5 to 5 doesn't really work as advertised, since you are putting the quantity of fuel for the larger 5HP displacement into the smaller 3.5HP displacement engine.
Tach was on the same setting for both engines. Its possible that we would see higher RPMs for both engines on a canoe for example...but in the tank...same load. Equal as I could make it.
@@TheMarineDoctor no worries. Just that I have a 3.5 merc. I put a tiny taco on her running in a tank…and it’s way more rpm than shown in your video there. On a 2.5m rib, it shows over 5000 rpm. Think it was nearly 4000 rpm in the tank from memory.
The only difference is carburetor jetting and prop pitch. I bought a used but like new Tohatsu 2.5 which is the same as the Merc. $86 in carburetor jets and a new prop and I have a 3.5.
I tried and didnt notice any difference in power. The after market 3.5carb i installed allowed me to start it in one pull rather than 2, though. @@TheMarineDoctor
Made by the same company. Decals are the only thing different.,edit. Same motor same parts. But I think parts as they come out are graded. Tohatsu makes Nissan even. Tohatsu is what you want
In all likelyhood not much difference outside of cost and a bit lighter. Prices may vary from dealer to dealer. There is not much $$$ to be made with the small engines.
Ran across this video a few days ago after picking up a non running 2.5hp mercury. Was told that a shop cleaned the carb but recommended replacing due to in being pretty gummed up. Also had to plastic weld the neck of the fuel tank. I found the part number for the carb had been superseded a couple of times and not available. Ordered a 32 dollar carb off amazon that was for a 3.5, 4 and 5hp model. Outward appearance was the same but after removing the old carb, I noticed the throttle plate and bore to be much smaller than the replacement. Engine runs great with no way to compare with the original since It was non running when I got it.
The good thing is there actually "IS" a difference!
WAYNE THE BOAT GUY!! I AM A FAN
I bought a 2.5 long shaft to replace my 3.5 short shaft because it was too short and then just disassembled my 3.5 to keep for parts and placed it all in a bin. I took the 3.5's carb and swapped out the brand new 2.5 carb. It was definitely different and i picked up about 1/2 to 1mph on the pond prowler in the ocean. That range was dependent on headwind, swell and current. I plan on taking out the high speed jet and drilling it out a little bit at a time and then running each mod and checking the soark plug after each hour run to make sure i find the perfect ratio before it gets too rich. I aaked the people that sell the 5hp upgrade carn about why its 5hp and all i got was "Duhhhhhhh.... We dont know..." Yeah right. Anyway, it has to be the jets. All of the specs and bores are the same on their 5hp carb compared to the 3.5 carb. Stay tuned.
Awesome. Thank you for that. Looking forward for the results.
My 2.5 is pretty slow I wanted a bigger motor but found a 3.5 cheap in good working order. Its not much of an upgrade but at least I will get out of the canals a little quicker on my12ft sea nymph. This video made me glad I got it. I saved 1K over the new 4hp . Its a 2009 4 stroke low hours got it for 300
Great video. I have a 3.5 I’ll be putting on my 12’ tinny this summer. I’ve seen them plane here on RUclips with an adult. So if it’s the difference between planing or not, for me the $300 is worth it. I also got a metal prop for mine.
What difference would this make on the water. ? In mph ? On a small 2.5 meter inflatable.
@@rainerneumeister5239 Very minimal. Maybe 1-1.5 mph
@@TheMarineDoctor ok. I thought these motors were suppose to rev between 4500 and 5750 rpm. ? We're your readings 2380 and 2750 rpm.
The 3.5 was running more solidly for sure.
I've been waiting for a video on this subject for years!!!!
(MY Mercury 2.5HP to 3.5HP conversion.)
I have a question maybe you might help with.
I have the Mercury 2.5 HP four stroke outboard and I was wondering if it would be up-gradable to 3.5 HP by merely changing the Carb Jets. You stated that the difference in the two was the carb.. But check this out...
My basis for this theory arose when I was looking for parts online for the motor. (I bought the motor new from Academy back in (2013) It's a 2010. got figure... anyway.
As I was looking through the parts diagrams for the 2.5 HP and the 3.2 HP I noticed that ALL the engine parts are the same IE, SAME PART #s… The cylinders are the same size, the bore is the same, the stroke distances are the same. The ONLY differences I could find ANYWHERE were Main jets and Slow jets. They had different part #s. The part number for The Carb Housings are different too... BUT EVERYTHING ELSE IS THE SAME.
So in my “Genius”, I figured that if I were to replace the 2.5 HP’s jets with jets meant for the 3.5 HP, the power should increase.
"Larger jet(s) more fuel flow". Now I’ve already bought the jets (but not installed them yet) and I was thinking that the jet holes on the 3.5’s will be a little bit larger, letting in more fuel… and thus producing more power at the throttle.
I don't have a tachometer... So-
I’m thinking the simplest, quickest way to see if this works would be to run the motor in its original state and record the High and Low speed sounds from a certain distance… Then change out the jets and record the High and Low speed sounds of the motor again. Then compare the before and after sounds to see if there is in fact a difference. I know this is a cave man approach to a comparison but again I don't have a tach. I might do a speed test on the water test, who knows... anyway.
Does this Rational make since to you?
Thanks.
I have not taken the carbs off and measured, but I would assume we are able to flow more air through the throat of the carb. This would then allow more fuel and higher rpm. Just adding more fuel should have a negative effect on top end performance. As for recording sound and comparing...perhaps you may hear a difference...but if we are flowing more air and fuel, it will sound different anyway. If you were able to modify the air flow. On the larger engines, air flow is restricted with a grommet. So they can use a single intake version across all the engines.
@@TheMarineDoctor Yeah when I saw that the carb had a different part #, I hoped the air intake was not too different to work... I've noticed that I hit top end (max rpm) way before I run out of throttle at the tiller, about half way... Kinda weird... Out of curiosity, I ordered and picked up the 3.5hp version of the main jet and slow jets sometime ago. I'll try to come back and let you know what the results are. As I said before your video was the only one that I've been able to find that even touched on this subject. Thanks.
@@TheMarineDoctor Oh PS, I'd be very interested in the throat sizes..
So the difference between the 2.5 and the 3.5 is the carb. So rather than just buying jetting, one could theoretically upgrade by buying the carb. Ok, so the upgrade I see a lot of folks making on the 3.5 is the 5hp prop and carb combo. Being the only difference between the 2.5 and the 3.5 is the carb, could the 5hp conversion kit be theoretically installed on the 2.5?
5hp is a larger displacement engine. 4hp 5hp and 6hp. So no. I do not believe so.
I ordered the 3.5 to 5hp upgrade kit. My suspicion is that it's a larger throat carb that's meant to mimic the performance of a 5hp on the 3.5hp base. If it doesn't work I'll be out a couple of bucks but filled with knowledge.
@@ethanschmidt7781 link please.
There are a few folks on RUclips who have tried and indicated that the 3.5 to 5 doesn't really work as advertised, since you are putting the quantity of fuel for the larger 5HP displacement into the smaller 3.5HP displacement engine.
Is that tachometer on the right setting ? Thought it would be more than that
Tach was on the same setting for both engines. Its possible that we would see higher RPMs for both engines on a canoe for example...but in the tank...same load. Equal as I could make it.
@@TheMarineDoctor no worries. Just that I have a 3.5 merc. I put a tiny taco on her running in a tank…and it’s way more rpm than shown in your video there. On a 2.5m rib, it shows over 5000 rpm. Think it was nearly 4000 rpm in the tank from memory.
@@Qbhoy79 prop the same?
@@ct1762 just the prop supplied from new. The rpm range on the 3.5 is 5000+ full throttle, I’m sure. Might be wrong.
@@Qbhoy79 I have no doubts you were able to hit higher rpm on the lake. The tank is not as forgiving.
The only difference is carburetor jetting and prop pitch. I bought a used but like new Tohatsu 2.5 which is the same as the Merc. $86 in carburetor jets and a new prop and I have a 3.5.
Do they start when shifted in forward gear?
You cannot pull on the starter cord when it is in gear. It is locked out.
@@TheMarineDoctor Oh, thought that the start lock is only on the bigger ones
!
@@bushpig8109 I stand corrected. I just walked up to the front and tried a couple. They WILL start in gear. Sorry.
Can I swap the carb on my 2.5 with the 3.5 carb? I can't find a aftermarket 2.5 carb but 3.5 are everywhere on ebay cheap.
Yep.
Will then be a 3.5 hp?
@@earlmcginty5355 I believe that is the only difference
Can you convert the 2.5 into a 3.5
Might be as simple as changing carbs.
I tried and didnt notice any difference in power. The after market 3.5carb i installed allowed me to start it in one pull rather than 2, though. @@TheMarineDoctor
Made by the same company. Decals are the only thing different.,edit. Same motor same parts. But I think parts as they come out are graded. Tohatsu makes Nissan even. Tohatsu is what you want
$150 with online outboards. Why such a big difference with you guys ? It’s diffidently worth an extra $160. Thanks for the video
Canadian pricing maybe?
I need your help.🤔
3.5hp or 4hp?
Thanks
100% 4hp
Wonder how this compares to the Suzuki 2.5? Is mercury or Suzuki better? I know the Suzuki is lighter. Suzuki also has a better price.
In all likelyhood not much difference outside of cost and a bit lighter. Prices may vary from dealer to dealer. There is not much $$$ to be made with the small engines.