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Old 25 September 2008, 06:01   #1
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Country: Other
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Make: Honwave Air 3.2
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Engine: Tohatsu 18 2 Stroke
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Tuning a tohatsu 18 (2006) 2 stroke

I have much experience in tuning and modifying 4 stroke engines for rally cars from my 'yoof' .. I would like to take time in the coming winter here in the sun to mod my tohatsu 18 2 stroke, - if practical and worthwhile !.

I also have on the yacht, polishing / grinding gear, accurate measurement devices, tools etc. no lathe lol, only 10.5 metres !!!!!

Any suggestions. ?
The ouboard does not get that much use, it is not run everyday, so an increase in fuel consumption is fine if applicable. Shortening of outboard ultimate life is also not too much of a worry due to the above.

I can find articles on the net for general two stroke tuning, but would like, if possible, something slightly more specific.
Any tohatsu bods out there that can advise, or general 2 stroke tuners ?. I have the workshop manual.
Adding carbs as opposed to 'carb' seems a tad difficult, but maybe you know otherwise...
any porting, flowing, exhaust mod etc recommendations, or whatever.

Cheers n beers.
Ruds.
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Old 26 September 2008, 06:28   #2
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Max overbore, sleeves etc, stroking ?

To add to the above, has anyone got any info on the max a towy 18 could be bored out to, how about fitting sleeves ?, or crank stroking ?
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Old 26 September 2008, 08:25   #3
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Fastfred is the chap to speak to if he is still around.
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Old 26 September 2008, 12:17   #4
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Boat name: Nautile
Make: Sea Rider Boats
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Engine: Tohatsu 18 /30 HP
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Quote:
Originally Posted by ruddles View Post
To add to the above, has anyone got any info on the max a towy 18 could be bored out to, how about fitting sleeves ?, or crank stroking ?
Don't touch your engine, the only update assuming about would be to update to new 2008-20 HP. Same 18 block with slight wider cylinders & pistons than standard 18. Don't think is a downrated 25 HP. The 18 is a excellent light/powerfull engine as it is, better than any 15 out there. No more production on 18 HP, just new 20's, so adios, farewell for ever.

Happy Boating
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Old 27 September 2008, 05:06   #5
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Thanks again guys

Have found a source for high spec reed valves for this unit, will see what else turns up.
Joe
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Old 28 September 2008, 02:18   #6
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Originally Posted by ruddles View Post
Thanks again guys

Have found a source for high spec reed valves for this unit, will see what else turns up.
Joe
I havnt got any experience on the 18 but ive been researching into this myself....
Changing reeds doesnt usually give you any more power-a test was done back to back with various different reeds in USA a while ago and if there was any increase, it was very minimal-usually gave the same power and some lowered the output.They dont last very long either-the oe ones are good enough.
The only real gain by adding carbon reeds is if one breaks it doesnt mash anything in the engine as it goes through as they break down easily.
You could try leaning the carb mixture out a bit and playing with the timing advance-but keep an eye on the plug colour(im sure youre well aware of the consequences of det and lean running).
Upping the compression ratio could help by milling a bit off the head and matching the the ports to the liners in the boars will aid flow but dont go opening the ports up unless you are willing to buy a new block if it goes wrong.
Polishing the crank case is supposed to make a bit of power too.
Opening the carb throat out a bit and removing the inlet resonator will get more air in.
Worth trying different props-ie thinner stainless ones.
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Old 29 September 2008, 13:02   #7
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Better buy the new Toh 20 HP and forget all the waisted time performing and testing tech modifications to this engine....
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Old 20 August 2010, 05:33   #8
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Tohatsu 18 tuning

If you want more power of the engine youŽd better listen to the right people.

Big bore pistons suzuki dirt bike 63 mm.
Tohatsu 50 hp. carb with taller and bigger main nozzle.
main jet 155
bigger reeds of carbon.
megaphone tuner.

your engine has about 21 hp. stock.
with theese mods you have about 25 hp.
The speed will increase app. 5 knots which is
faster than any stock 20 hp.

those people who do not know anything about tuning tohatsus should be quiet

Everything is easy if you are easy!
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Old 20 August 2010, 16:51   #9
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Ran.

Did you look at the posting dates before your rant????

Ian
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Old 20 August 2010, 18:39   #10
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JESUS, HOW MUCH HP DO YOU WANT FROM A STANDARD 18HP

If you manage to get 22 safely, IS IT WORTH IT.?????????????/

Just by a bigger engine its cheaper!
Howy
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