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Old 11 June 2018, 12:05   #1
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Tohatsu 25hk

I habe a Tohatsu 25hk two stroke (i belive it is a 2003 mod) and i would like to get it op to 30hp. I have heard that you only need to change the gasket between the carbuerator and the cylinder. Is this true or do i also need to change the main jet?
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Old 11 June 2018, 16:54   #2
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Welcome to the forum.

You need to do a little detective work to answer your question. Tohastu outboards, especially 2-stroke can be tweaked. My M60C uses the same block of the M70C and the only difference is the main advance arm needs adjustment to allow full throttle opening.

On the 25hp, 2-cylinder block you'll need to cross check against the 30hp to ensure it doesnt have an increased exhaust manifold, restricted carbs, or indeed a different inlet reed valve.

2003 25hp
https://www.boats.net/catalog/nissan...-stroke-nissan

2003 30hp
https://www.boats.net/catalog/nissan...-stroke-nissan
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Old 11 June 2018, 17:17   #3
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Thank you on a norwegian site they explained that it is a gasket restricktor (didn't manage to upload it here), if there is a gasket type restrictor on my engine will i need to upjet?
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Old 11 June 2018, 20:03   #4
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Quote:
Originally Posted by jonaseriksen01 View Post
Thank you on a norwegian site they explained that it is a gasket restricktor (didn't manage to upload it here), if there is a gasket type restrictor on my engine will i need to upjet?


The only way to be sure is to get the parts diagrams out and compare side by side.
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Old 13 June 2018, 02:14   #5
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I think you are correct in saying it's just a gasket behind the carb, you can either order a 30hp or just open up the 25hp I believe. I've never done but remember reading on another forum, maybe worth checking the parts book for both engines, just quickly check exhaust part numbers and maybe jets too
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Old 01 June 2019, 07:40   #6
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Hi guys.

Did we ever get to the bottom of how to do this?

I've just acquired a YL380Dl with an old Tohatsu 25Hp 2 stroke and have been through all the carb parts list and there doesn't seem to be any difference at all in the 25-30hp parts.

Could it just be a throttle restrictor to stop full RPM?
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Old 02 June 2019, 14:19   #7
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25HP to 30HP Factory Conversion.-

There's 2 issues associated with upgrading a Nissan/Tohatsu 25 to 30 HP :
-It's a carb gasket swap, buy the 30 HP model, has wider air intake.
-Time advance on both are different, the 25 model works with 20, the 30 model works with 25 timing.
-Both models shares same exact parts except the carb gasket.

Adjustment Procedure :
-Remove cowl.
-With left arm finger press butterfly's pawl fully down to open the butterfly fully.
-Hold it there, with right hand throttle grip back and forth from 3/4 to full grip.
-Check if hearing a slight banging going on between cam actuator and white roller.
-If the slight banging is not heard means the carb remains adjusted to the 25 model.
-Without releasing pawl nor throttle grip.
-Stand at middle right side of motor and visually check at which timing mark is timing plate stopping at ?
-If stopped at the 20 timing, will need to adjust carb and timing to 30 HP specs.
-If stopped at the 25 mark leave it there, make sure has stopped at middle of both mating surfaces as in pic, if not will need a slight adjustment.

Note: could have a case in which carb doesn't open fully but motor was delivered with 25 setting, as have found out checking may 25 HP motors.

What's the prop number stamped on current prop ? Report your findings to go from there step by step.

Happy Boating
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Old 03 June 2019, 12:17   #8
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Update, forgot to mentioned that after the motor cowl has ben removed, with throttle grip fully turned to min throttle position, must move gear lever to forward position, from there can continue with the process...

Happy Boating
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Old Yesterday, 12:15   #9
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Hi guys

Quick update.

As per Locozodiac has explained.

Very simple operation to change the carb gasket and its exactly as Loco's pictures.
New Wider open gasket fitted.

I test fired the engine on muffs and all started fine.
I've adjusted the timing one notch as instructed.

Not sure if its important but after adjusting one notch forward I realised I still have another notch marked on the timing marks to advance more.

This would either mean my engine was set at 15 degrees by the previous owner and I've adjusted to 20 or there is another setting marked on my engine to maybe go to 30 degrees?

Haven't had a chance to get it in the water yet to open it up (first week of August I'll have it in the sea in Cornwall) but it fires up fine and ticks over on the muffs perfect.
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Old Yesterday, 17:16   #10
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Counting from 0, you should advance the timing 6 full (l) marks till reaches 25 timing mark as previously described. Don't recall if there's a seventh timing mark pass the 25 one. If so don't use it , motor will have excessive time advance for the max fuel intake achieved at 25 deg for the 30 HP motor.

If in doubt, post a clear picture shot in front of both mating surfaces. Which is the current pitch number stamped on prop body ? Is it a 13 ?

Happy Boating
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