Another prop suggestion needed

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uglymud

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Well I have a 25 hp three cylinder yami on a 16 foot flat bottom jon. Right now I'm running 30 mph with a 14p aluminum prop at 4500rpms according to my tiny tach. I was thinking about stepping down to a 12p, thoughts?


Also just wondering if I have my tach set right, shows idle at around 600rpms. Wondering if anybody knows the correct degree setting?

Thanks
 
whats the diameter and pitch of ur prop? whats the max rpm operating range for your motor??? those rpms seem low but that may be cuz its a three cylinder
 
RPM is 5500-6000 max. That is what Yamaha calls for obviously on a stock motor. So many of them get modded, and then the factory recommended max rpm goes out the window at that point.

Powertech SRA3 13" is what I would recommend. Look for low 30's at 5600-5800 RPM. 600 RPM is pretty close. They will idle down great. Of course that's assuming it's not been modded. Start porting the block, bigger carbs, etc, and they generally won't quite go that low after mods.

Mods? How much power do you want? They'll make 80 hp+ but reliability goes down the tube. Guys tend to argue that but trust me, once you get to a point, you work on a modded motor more than you use it.
 
Alright thank you I'll put in an order for one.
As far as mods go when I bought it the fella said it had head shaved, carbs re jetted with 30 jets and exhausted opened up.
I plan to get some tohatsu m40d carbs in the future with a performance head and tuner. And possibly new pistons, atleast new rings.
 
turbotodd said:
RPM is 5500-6000 max. That is what Yamaha calls for obviously on a stock motor. So many of them get modded, and then the factory recommended max rpm goes out the window at that point.

Powertech SRA3 13" is what I would recommend. Look for low 30's at 5600-5800 RPM. 600 RPM is pretty close. They will idle down great. Of course that's assuming it's not been modded. Start porting the block, bigger carbs, etc, and they generally won't quite go that low after mods.

Mods? How much power do you want? They'll make 80 hp+ but reliability goes down the tube. Guys tend to argue that but trust me, once you get to a point, you work on a modded motor more than you use it.


hey turbotodd, im just curious? how is it possible to get 80hp from a 25hp powerhead? I know Johnson/evinrude 20-35hp powerheads and if you have a 20-25hp motor you can get the 10-15 more hp on most models and make it 35 but 80hp from a 25hp powerhead seems to me like it would not be possible but I know nothing about yamamamas.....
 
Big bore carbs, cylinder head and mods, exhaust tuner, exhaust cover, port the block, lightened flywheel, 8500 RPM, etc etc.

out here where duck hunting has turned into not much more than "boat races", the 3 cyl 25 and the "mega 25" (tohatsu) rule the races. Some guys are using them on 15' jons running upwards of 60 mph.
 
turbotodd said:
Big bore carbs, cylinder head and mods, exhaust tuner, exhaust cover, port the block, lightened flywheel, 8500 RPM, etc etc.

out here where duck hunting has turned into not much more than "boat races", the 3 cyl 25 and the "mega 25" (tohatsu) rule the races. Some guys are using them on 15' jons running upwards of 60 mph.


by big bore carbs what do you mean? cyl and head mods? (bore them out?) exhaust tuner and cover??? port the block? could you explain a little more? or send me a PM? thanks
 
60 mph out of a modified 25 Yamaha is an exaggeration. Yes out of a modified fega and a modified Mercury. But even those guys aren't running that with their hunting props. If you are wanting to get work done I'd look up cuz outboards, metro outboards, 4 am motors, ect and send your motor to them after duck season and call now to get on their list
 
I'll back turbotodd up on this. You can get a lot more power out of a loop charged triple. Pretty sure they use carbs off a 50hp tohastu or something like that for the big bore carbs, fiber reeds, custom exhaust tuners (shorten the stock exhaust or cut off the stock exhaust and weld on a "megaphone" or "cow bell" shape exhaust) shave the head to up compression, port the cylinders to bring in more fuel and air ( widen or raise the port windows), add finger ports for even more fuel and air(2 extra ports in between the transfer and intake ports that are feed through a hole high in the piston skirt.). Setup right I wouldn't be surprised to see these boats in the high 50's. Not sure they're making 80hp, 50hp is probably do able out of the true 25hp triples.
 
Ya I'm not trying to call him a liar. Just haven't seen it. My friend had one one a 1648 war eagle and his hunting set up was low 30's. It wasn't as heavily modified as yall are talking about though.
 

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