Tohatsu 25hp to 30hp ?

[scott_b]

Gday
Can anyone tell me what has to be changed to convert a 25hp tohatsu to a 30hp. Looks like there is a restriction plate behind the carby that can be removed. Is there any other mods that have to be done. ???
Any help would be grately appreciated
wamjam

[NQCairns]

Hi dont know the specifics of these, but the 1/5 extra hp will be made only in the uppermost RPM portion. The engine probably will have less pickup across it's entire rev range untill reaches the high end then it will just go a few km/h harder.
Things to check may be carbie bore, exhaust tuner, inlet and or exhaust restrictors and of coarse middle and upper jetting, also might need a retime to suit the differing higher rev range. Good luck it usually doesn't end well these mods but the Tohatsu may be a different animal? Have you heard they convert well?nq

[scott_b]

Gday nq
Had a look at the specs and they are identical eccept for the rev range .The 25 is 5000 to 6000 and the 30 is 5150 to 5850 and I have heard that you have to remove the restrictor behind the carby and change the timing. Don't understand the loss of revs for horsepower but thats what the specs read. Apparently the 30hp light weight merc is a 30hp tohatsu. I just don't know. ??? ???
Scott (wamjam)

[NQCairns]

Thats interesting, some O/bs are souped up to make a higher HP and very few are de tuned to reach a lower HP sounds like you may have the later. Thats good news if a person wanted a robust and torquey 25hp also good news for the 30 as well.

I really am guessing here but the rev ranges hint at only restrictors it may even run identical carby bore and jets etc I would try and check out the 2 engines carby kits and standard jetting. if they are the same you will not damage it by pulling any restrictor you find. I would also check just how different the timing is on both also and consider doing that as well before any WOT runs.
Just a note : the rev ranges you gave are the engines operating range which actually means - the range we give to satisfy the gov regulations so that the engine can give 100hp at the prop at 4650rpm and when the punters buy it and run 5400+rpm and make 115hp at the prop they tell there mates how fast it is and we sell some more ;D ;D
The engines real operating range is actually 5600 to around 6200 goes for virtually all the carb 2 strokes.
If you got it sorted minus the plates or whatever is the real deal and propped it to spin high in it's range like 6100 to 6300 you might be making near 35 hp :o :o Good luck let us know how you go.nq

[aquarius]

Gday nq
# # # #Had a look at the specs and they are identical eccept for the rev range .The 25 is 5000 to 6000 and the 30 is 5150 to 5850 and I have heard that you have to remove the restrictor behind the carby and change the timing. Don't understand the loss of revs for horsepower but thats what the specs read. Apparently the 30hp light weight merc is a 30hp tohatsu. I just don't know. ??? ???
# # # Scott # (wamjam)
Yes that is correct....my mate owns a light weight mercury 30 hp(30 HP TOHATSU)