BF25 4 Stroke upgrade to 30 Hp HELP PLEASE

[johnalan42]

Hi there this is my first post,hope someone can help/advise.
Im running a new BF25 on a 700lb 17 foot fiberglass boat( "Orkney 520" to be specific.)
i wish to modify the engine to give me the extra 5 hp available as the 25 hp & 30 hp engines are the same apart from jetting ( i,ve been told) is it just restrictor washer or something simple???

This leads me onto a second question relating to a spare prop, looking for something possible coarser pitch as engine is not reaching into manufacturers max yet....but it might once de- restricted. That might possibly lead me to getting a Finer pitch for more top end speed.
Current prop 9-1/4 X 12"
Any suggestions please.My problem is too many variables and no good solid info. Thanks John.

 

[Wee Hooker]

Re: BF25 4 Stroke upgrade to 30 Hp HELP PLEASE

This has been discussed here a few times. Hit the search button. You don't mention model year but if it's one of the new fuel injected units, you'd need a new ECM (read: $1000+)

As for pitch, that motor is way over pitched. I'm running a 10Px9.9D on my 30 Nissan (pushing a 800# (fully rigged but without people) 16' boat and I'm just under 6250 RPM.

 

[johnalan42]

Re: BF25 4 Stroke upgrade to 30 Hp HELP PLEASE

Yep thanks for that. It is a 2007/8 model. Typical about the ECM. Also interesting about the prop pitch. I am surprised that this is the factory choice.
Thanks again for your info.

 

[marquette]

Re: BF25 4 Stroke upgrade to 30 Hp HELP PLEASE

i don't know how my 1998 BF30 compares to the 2007/8 model but i have the factory repair manual for the 1998 BF25/30. repair procedures are the same for both but there is a several page suplement to cover the differant tune up specs and parts for the BF30.unless you had a junk 30hp to get all the parts off of it looks like a fairly expensive upgrade for 5 hp. probably better off to trade in for a 35hp. the 35 & 40 have a better prop selection also.

 

[johnalan42]

Re: BF25 4 Stroke upgrade to 30 Hp HELP PLEASE

Yep thanks for that. My problem is that the Hull is rated to Max 35.They used to be 30Hp,on the older model called a Strikeliner. Never thought that i should max it. Thats why i plumped for the 25. Knowing also that it (The 25) is really capable of being a true 30 and therefore never being under too much mechanical stress/load.Ill try different props first i think. Cheers again.

 

[Wee Hooker]

Re: BF25 4 Stroke upgrade to 30 Hp HELP PLEASE

FWIW, Mercury's site shows some performance specs of different props on 25-30 4 strokes. My guess is that a 10 would be about right but that's just a guess. ( That's also what the factory guessed for my dealer too.) I'm going to try an 11 on my rig for giggles as that is what I bought (cheap off Ebay) for a spare. You really want to get a tach if you drop too low as you need to be concerned about over reving. ( Rule of thumb is that for every inch decrease in pitch will give you 200 RPM increase +/-_ )You might want to check over at the prop section for more details.