converting 15 HP Mercury bigfoot to 25 HP

[Hawgwild]

I have a new Mercury 15 HP bigfoot and have heard that the only difference between the 15 and 25 is the carb. Is this true? I have to use a lid with 15 HP on it because a lake reg in my neighborhood. However, if at all possible, I would like the boat to plane out.

 

[Barlow]

Re: converting 15 HP Mercury bigfoot to 25 HP

welcome Hawgwild .. <br /><br />best to post this up in the Merc forum or on the outboards non-repair ,, <br /><br />good luck with it

 

[JB]

Re: converting 15 HP Mercury bigfoot to 25 HP

Outboard Non-repair. On the way.

 

[JB]

Re: converting 15 HP Mercury bigfoot to 25 HP

Think about it, Hawgwild. Does it make sense that a different carburetor would produce a 67% increase in hp? Not a chance.<br /><br />What boat do you have your 15 on? perhaps some prop and rigging tuning can get it on plane.

 

[Silvertip]

Re: converting 15 HP Mercury bigfoot to 25 HP

The 15 HP engine is 323cc displacement while the 25 is 498cc. Ironic that the displacement increase is roughly 60% and HP increase is 67% as JB indicated.

 

[Hawgwild]

Re: converting 15 HP Mercury bigfoot to 25 HP

That is what I figured but I wanted to check int oit anyway. The boat is a Fisher 1710. The boat is wide and heavy but so is my rear end. Seriously, I wanted something stable for the kids when they are with me.<br /><br />If you guys know of anything that could help me get it to plane out, I would appreciate it. Otherwise, I appreciate the time that you have already given me.

 

[Chinewalker]

Re: converting 15 HP Mercury bigfoot to 25 HP

Hi Hawgwild,<br /> The best fix for your issue is to get a bigger motor. Your 15 has a fair amount of value, so the overall difference between the two shouldn't hurt the wallet too much...<br /> Good luck!<br />- Scott

 

[KM2]

Re: converting 15 HP Mercury bigfoot to 25 HP

Hawgwild, the march 05 issue of Bass & walleye boats mag did a story on turning a 9.9 to a 15 with carb change and a few small changes. They used the parts lists to compare motors and see what the differences are. In this case the carb was abjout the only diff so it worked. <br /><br />I agree with the posts that it's not likely your 15 can be upgraded very easily. Maxing out the set up is your best bet. You can learn a lot by searching iboats looking into props, tabs, foils, engine height etc...

 

[WillyBWright]

Re: converting 15 HP Mercury bigfoot to 25 HP

In general, 9.9/15 motors are completely different than the 20/25. 15 is the most they get out of that particular block. I'm afraid that your biggest problem is that it's a Bigfoot. Those aren't made for speed. They're specifically made for pontoon boats and similar applications and no dealer should ever sell them otherwise. That shows a certain degree of ignorance of the product they're selling and I wouldn't buy a sparkplug from them. <br /><br />Now regarding your cheating on the local laws. What do you think the warden is going to think when a boatload of people is planing along with a "15Hp" on the back and everyone else putt putting along watching you? You're automatically on his "First to pull alongside to inspect" list for that day. I hope you have deep pockets, cuz the motor is just where they'll start. Any additional violation(s) they find will be added right in. Make sure to have a paddle along because they won't let you run it or tow you back.

 

[roscoe]

Re: converting 15 HP Mercury bigfoot to 25 HP

IMO, the biggest problem is a restrictive law governing hp on your lake. Work to change it or move.