newbie here looking for some ob knowledge

[big tom]

Hey guys, been following your site for a couple months.. awesome!. I hang out on offshoreonly.com in the summer and dootalk.com (snowmobile/ski doo) in the winter.
I have been a boater all my life in Michigan, expect for last year I tired taking a year off. Never again!. I have had pantera's, Carrera's and a couple Baja's in my early years. So I recently picked up a 1999 31 fountain cc with 1999 250 efi's, I belive 1.75 case's and quick sliver 4 blade props... all greek to me some what. I do run 2 stroke snowmobiles with big bore kits and etc and have been a gear head all of my life.. I have never owned any thing bigger than a 40 merc. in outboards so I have been reading and searching for some knowledge. You guys seem to be the best outboard site I have found!. I would like to ask a few questions..

Were is the best place to buy a merc manual.?
I burn blue marble in my sleds, but there was quicksilver prem plus syn bend in the tanks so I grab a couple cases for now. good?.
I have been on simon motorsports looking at ecu flash, poppet deverters and flywheels. Are these good gains?
I have been on brucato looking at reed plates. good gains?.
Are the 4 blade props spinning outwards a good set up?
On the upper mid section in the back there's a plug that's for?.
Is there any down falls to having 1999 250 efi's..

I better stop there, I don't want to wear out my welcome... thanks tom

[sleek150]

Quicksilver has been good to me, there are other options but the availability of prem plus makes it my current oil.
Not sure about ecu's and flywheels but like any engine the best gains on these outboards come from head mods (shaving the heads) contact Jay Smith Racing Engines. He does a lot of them
The only down fall to those 250efi motors are the rpm limiters. if you want more speed you need more rpm's
you will have to give more details on the prop question mph, rpm, pitch, exact prop

[outasite]

Oil is good,rotation good,as said above a cut on the heads,and a reflash of the ECU is next.Post some pics of the rear of your boat out of the water.You will get more,and better info!!!

[big tom]

The head cut would take the compression ratio to around ?. Or should I say what compression ratio am I looking for on pump gas?. And is the squish band changed?. I've been fueling on land 91 octane E-free or on water rec fuel at 90 octane. I know on 2 stroke sleds we try and stay @ 12.5 to 13:1.. 13:1 is on the edge for 91-93 octane pump gas

[big tom]

https://www.youtube.com/watch?v=xJug0oN2uyM Can't get pic's to load, this is the video the broker made. Does show motors and stern of boat . I have detailed boat and it looks way better than video.

[outasite]

You want to see cranking compression of 140/145. Someone here that runs the 250s will be able to tell ya how many cc your looking for.

[sleek150]

Yes the squish will change. That is why these motors respond well to shaving the head. An optimized squish will increase turbulence in the cylinder and provide for a more atomized fuel mixture resulting in maximum combustion. The added compression also adds power. Jay Smith will be able to get you the right numbers. Contact Jay Smith Racing Engines. I hear he is the man with the plan

[big tom]

Thanks for the info guys!. In the 250 merc do they use nic or steel bore?..


After doing some search I see a lot of older posts including jay smith are running penzsoil xlf-tcw3. Is that still the case?.