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Old 20 July 2008, 19:24   #11
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Originally Posted by Chatts View Post
Thanks. Got the gasket, will try fitting it at the weekend.
If the 25 HP were so simple to convert to a 30 HP or viceverse as Turbo states, that is remove the air restrictor plate and change a simple gasket there wouldn't be a + $ 200 dollar or more price difference between these two 52 Kg same size, single carbed 430 CC twin cylinders engines. According to Tohatsu service manual there are some parts differences between both models like: Intake Manifold, Carbs, and some small parts. Have written the Tohatsu factory to inquire 10/15 25/30 engine conversions, as am most interested to perform correct uprates for clients. Will wait for the factory technical vredict.

As a comment, had the opportunity to instal 2 new 25 & 30 HP Tohatsu (Mariner Marathon) engines in 2 different size sibs, the 25 was factory delivered with 20 advance timming mark, the 30 with 25, in other words the 25 didn't reach full wot, the 30 did. Remove air plate restrictor, look for your 25 HP to reach full wot (throttle), adjust by means of the fully open stopper arm to be in the 30 HP range. Cruise experiment with removed/changed parts.

Would like to know if the performance was bettered with a simple restrictor plate removal & gasket change ? Fingers crossed!

Happy Sibbing
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Old 21 July 2008, 06:05   #12
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Originally Posted by Locozodiac View Post
If the 25 HP were so simple to convert to a 30 HP or viceverse as Turbo states, that is remove the air restrictor plate and change a simple gasket there wouldn't be a + $ 200 dollar or more price difference
you think?
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Old 21 July 2008, 07:10   #13
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Fitted new gasket yesterday. Very simple, took 5 mins.

Literally undo the 2 nuts holding the carb on, pull carb forward (no need to undo the linkages), take the old gasket out (is clearly restricted as has rectangular slot for air to get through whereas the new gasket has big hole same size as the hole in the carb), put new one in, put carb back and tighten nuts.

Didn't change the jets or fueling, it started and ran just as well as before and wasn't lumpy at all.

Out on the water there is a noticable difference in response and pull. Certainly accelerates harder and seems much more on top of the job. Before it would struggle to pull a doughnut (with an adult in it) but now just powers straight up onto the plane. Going to try skiing behind it next.

Don't think top speed really changed but guess you need a different prop to change that.

Seems to be a great mod for 9 (as long as it doesn't blow up!). I vaguely remember when I bought the engine a 30hp was about 500 more expensive!
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Old 21 July 2008, 17:03   #14
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Quote:
Originally Posted by Chatts View Post
Fitted new gasket yesterday. Very simple, took 5 mins.

Literally undo the 2 nuts holding the carb on, pull carb forward (no need to undo the linkages), take the old gasket out (is clearly restricted as has rectangular slot for air to get through whereas the new gasket has big hole same size as the hole in the carb), put new one in, put carb back and tighten nuts.

Didn't change the jets or fueling, it started and ran just as well as before and wasn't lumpy at all.

Out on the water there is a noticable difference in response and pull. Certainly accelerates harder and seems much more on top of the job. Before it would struggle to pull a doughnut (with an adult in it) but now just powers straight up onto the plane. Going to try skiing behind it next.

Don't think top speed really changed but guess you need a different prop to change that.

Seems to be a great mod for 9 (as long as it doesn't blow up!). I vaguely remember when I bought the engine a 30hp was about 500 more expensive!

Are we talking about Yamaha or Tohatsu rebadged to Mariner Marathon ? as both are two complete different engines. Both Tohatsu/Mariner 25 & 30 HP comes with the same prop for both, though both have different timming mark settings 20 & 25 respectively.

Can you post a picture of the old gasket changed, are we talking about the gasket located between the intake manifold & carb body ? or is a different internal carb gasket, did the 25 had an air restrictor plate which you have removed ?

Probably experimented a better engine response by having more air intake than previous gasket/restrictor setting, but really have uprated to a factory 30 HP by these simple changes ? As don't want to give a erroneous opinion about correct/incorrect conversions done outside by boaters, will wait for the factory tech dept response.

Bottom line: where the hell are the 200/250 dollars difference between both 25 & 30 models, can somebody give a technical non especulative answer ? As Chatts points out, 500 pounds of difference when he bought his engine, excesively expensive, a hand gun robbery indeed.

Happy Sibbing
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Old 21 July 2008, 17:08   #15
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you think?
Be my guest, espress your thoughts/ideas on this matter..but from a technical point of view that is.
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Old 21 July 2008, 18:22   #16
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Originally Posted by Locozodiac View Post
Be my guest, espress your thoughts/ideas on this matter..but from a technical point of view that is.
so you believe that engines are sold purely on a cost plus model? if customers percieve added value and are willing to pay extra - charge them extra.

[Even with several part variations - the costs of production will be almost identical anyway. Higher power presumably means high wear and tear - so increased warranty risk. Relatively small increases in cost at the factory amplify into larger increases once dealer & distributor markups and taxes are added].

and you think that TurboDiesel who works for Barrus, and has an excellent reputation here for quality advice on their engines doesn't know what he is talking about... but the guy in the Nissan factory is going to tell you the truth (not necessarily the official answer) about Tohatsu engines!
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Old 23 July 2008, 09:01   #17
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Originally Posted by Locozodiac View Post
Be my guest, espress your thoughts/ideas on this matter..but from a technical point of view that is.
Manufacturing cheapness comes with volume. If you can use the same parts on a dozen engines you have made all those engines incrementally cheaper 'coz you are bulk buying components - your buying punters pay for power, whistles & bells. As Polwart says, you're not just buying the "cost price" assembly - remember they have marketing, R&D etc etc to pay for as well.

Another good example is the 2hp units are the same engine with half a dozen paint jobs - classic example being the Merc/ Mariner / Tohatsu / Johnson & I'm sure someone else's paint job is carried by it 2hp 2- stroke. Your buying punters buy them to get out to their yacht - selling cost is king, features are irrelevant- the fact it doesn't talk NMEA to your all singing & dancing plotter for fuel economy monitoring is totally irrelevant. The profit on these units is miniscule - only one OEM needs to develop it, they get paid for the design by selling it to whoever wants to put their name on it and double/triple/quadrupling their volumes.

Another example of this is the old Suz DT25/30. The change there was slightly more clever (on Suz' part) - they changed the throttle stop stamping that is welded to the end of the throttle shaft - the subcomponent that cost all of (I conservatively estimate) about 10p to manufacture is welded onto the end of the shaft, so if you want to upgrade you need to change the whole carb. I also believe they put a "firmwre" change in the CDI - Cost of that was about 2 lines of software code. As the CDI is a sealed unit, you also have to buy one of them, coz you can't break in to pull the chip & alter the code. (even if you had the equipment & knowledge to do so!)

So, to upgrade you need a new carb & CDI. Suddely 500 for a the next size up engine seems not so bad...... AND you get a bigger number on the lump on your transom! (marketing reason )


I can assure you no OEM will be giving you info like that through any "official" channels.
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Old 23 July 2008, 18:43   #18
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On roughly the same topic - what's the chances of upgrading a Yamaha (2-stroke) 3 cylinder 40hp to 50hp. I had posted this question before but got varying feedback ranging from 'cheaper to simply buy a 50hp' or 'its just a case of changing carbs (1/4 larger) and exhaust manifold.'

Would CDi have to be changed too? These retail for a couple of hundred quid second hand!!!
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Old 27 July 2008, 19:06   #19
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Resuming Conversion Post

Hi all, just returning to the city from installing 2 new surf towing 380 sibs powered by Yam 25 & Toh 30 HP. Reading lasts posts, there has been lots of answers, for a "conclusion finale", up to now the original poster has not provided an answer on :

1-Mariner 25 model year, color, etc
2-It's a Yamaha, Tohatsu rebadged Mariner ? If he dosesn'r know..
3-Post photos of engine interior prefferably both sides (to see it it's a cable or pinion arm aceleration throtthle: (Yam or Toh Mariner rebadged model))
4-If an air restrictor was found when the carb was taken apart ?

Vague post answers as to the vague imput. So to define and make a interesting Ribnetter post for other user as well who are intredted on conversion issues, will need to clarify all 4 missing points. If the original inquirer will not post the required info to continue the post, will leave the topic as un answered one. A pitty cause it's an interesting theme.

The post so far will not solve the original inquired conversion issue by lack of information as both Yamaha/Tohatsu rebadged Mariner models are completely different one from the other. I'm still saying that it's technical impossible that by a simple of a carb gasket you can uprate a Tohatsu 25 to a 30 HP, have at hand Toh service & parts manual 2.5 to 40 HP, 2 strokes and looking to some same parts on both models 25 & 30 like carb, maniford, slow jet the codes differs as from 25 HP codes.

Will provide in some days, as soon as I have the factory tech back answer, the correct conversion issue, have contacted also a Tohatsu enginer who prepares Tohatsu racing engines in many engine size categories, would like to hear what he says to say about uprating to match factory engines.

If the original post awaited answer is reffered to a Yamaha rebadged 25 Mariner, then some peeing has been done out of the bassin. Converting a 25 to 30 HP will not give you a much greater overall spped, will give you more power to push with same prop, if looking for more speed then perform the wot propeller test to reach max rpm rated for that engine.

To see the tech level of some "gurus" out there, will invite to post answers on a new thread Evinrude/Johnsons 10/15 2 stroke conversions, how are they made, any thoughts ?

John, if you are following this conversion thread, would like to hear your personal opinion about this speculative thread.

Happy Sibbing
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Old 27 July 2008, 19:15   #20
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Hi all, just returning to the city from installing 2 new surf towing 380 sibs powered by Yam 25 & Toh 30 HP. Reading lasts posts, there has been lots of answers, for a "conclusion finale", up to now the original poster has not provided an answer on :

1-Mariner 25 model year, color, etc
2-It's a Yamaha, Tohatsu rebadged Mariner ? If he dosesn'r know..
3-Post photos of engine interior prefferably both sides (to see it it's a cable or pinion arm aceleration throtthle: (Yam or Toh Mariner rebadged model))
4-If an air restrictor was found when the carb was taken apart ?

Vague post answers as to the vague imput. So to define and make a interesting Ribnetter thread for other user as well who might be interested on conversion issues, will need to clarify all 4 missing points. If the original inquirer will not post the required info to continue the post, will leave the topic as un answered one. A pitty cause it's an nice tech theme.

Both Yamaha/Tohatsu rebadged Mariner models are completely different one from the other. I'm still saying that it's impossible that by a simple carb gasket change you can uprate a Tohatsu 25 to a 30, could have a slight performance improvement but not a real factoy standard 30 HP. Have at hand Toh service & parts manual 2.5 to 40 HP, 2 strokes and looking to some same parts shared, like carb, maniford, slow jet, etc, find the parts codes to differ between both models.

Will provide in some days, as soon as I have the factory tech back answer, the correct conversion issue, have contacted also a Tohatsu enginer who prepares Tohatsu racing engines in many engine size categories, would like to hear what he says to say about uprating to match factory engines.

If the original post awaited answer is reffered to a Yamaha rebadged 25 Mariner, then some peeing has been done out of the bassin. Anyway whichever brand it is, converting a 25 to 30 HP will not give you a much greater overall speed, will give you more power to push more load better with same prop, if looking for more speed then perform the wot propeller test to reach max rpm rated for that engine.

To see the tech level of some "gurus" out there, will invite to post answers on a new thread Evinrude/Johnsons 10/15 2 stroke conversions, how are they made, any thoughts ?

John, if you are following this conversion thread, would like to hear your personal opinion about this speculative thread.

Happy Sibbing
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