Bumping up 1990 90 HP Crossflow to a 115? Help Champ!

[PhilN]

Need some help. Rebuilt my 88 HP, J88MFLESA because of plugged water passages from alkalai buildup from pyramid lake in Nevada and the timing adjustment rod nut came loose...anyways. Everything is top notch now. It was fun
tearing this motor down without any metric tools! Using a jetdrive and I need a little more power. Ive memorized the parts lists from the 90 and 115 hp motors. Part numbers for all parts are nearly identical except for carb orifices. How can I juice this 90 hp a little? Not a boat I want to spend money for a new motor and the little 90 is reliable but undersized for my Almar 16'. I like having a motor I understand..and know how to work on with a screwdriver and a 7/16" socket. Thankfully my 2006 Yamaha F150 has been perfect....��

[omcforever]

Fred, If you dont mind, I will address this. First of all it aint gonna happen. The 90/88 and 115 have different blocks and port timing. The actual carbs are different as well. 88/90 has 1 3/16 carbs and 115 has 1 5/16 carbs. Bigger orifices dont mean more hp. You hear all over the web and FB that all you have to do is rejet/recarb to gain HP. You may gain in some combos but you have to know what you have and what will work and will never reach 115 hp. Usually wind up with a gas guzzling, ill running mess and worse can wind up with a lean grenade ready to go boom. I have tried every combo known and have learned if you want 115 hp, find a 115(unless you have access to a machine shop and $$$ and know how to jet a frankenmotor). If you want a better running 88/90, insure it is up to snuff, linked and sync'd properly, install some Chris Carson reeds and let her rip(max timing 28 degrees with good gas). Mix/matching parts on the old crossflows can be bad and usually never equate to any noticeable gains but just headaches.(at the least)

[PhilN]

Thanks Art. Im looking hard for a 115 all over the place and will keep searching. Have a good weekend.

[omcforever]

If you happen to come across a 140 crossflow, steer clear. The 140 was from the early to mid 80's and used an entirely different exhaust tuner/megaphone which is scarce as hens teeth and different porting and port timing as well. Had entirely different electronics and carbs(1 3/8). Your model and year was limited to 5800 rpms or so and without the parts that are standard with the 140, could never reap the benefits of the 140's porting or carbs. The 115's of the 90's is actually a de-tuned version of the earlier 140's and in my opinion, the best V4 crossflow ever made(they all are reliable and work horses).

[PhilN]

I do have the factory manual and looking at the link and sync instructions. My jet drive makes it difficult for a water test..cant use a test prop. In the driveway with motor off at full throttle, the butterflies are a smidge less than full open. Opened them to horizontal on the water, under power and it obviously ran worse. Motor will only go 5200 rpms. Im sure its a simple adjustment and fighting taking it to a boat shop. Manual 508145 says 5500 is max rpms...and I only need 300 more. Timing and compression is good and checked. I did have every cable and wire unhooked...as im rambling, wondering if the throttle cable is pulling all the way? This is probably a very simple adjustment for someone. Is there a way check link and synch with the motor not running?

[Highthrust]

Running a jet you will need a lot of HP to notice any performance difference. If the motor isn't doing it for you. You'll probably need a V6.