91 jonnyrude115

[Merc 2.5]

Buddy mine called wanting me to do a tune up ,getting ready for spring

What can I do to this motor besides compression to help this little motor out , I'll optimize his setup for him also , reeds , stuffers? What bout timing on these motors?

[faztbullet]

Looper or crossflow?

[Merc 2.5]

I don't know , I haven't seen it yet he wouldn't know , I'll have to get him send a pic

[racer]

91 115 would be a crossflow. What can be done depends on what it will be used for and weight it will be pushing. IMO do not run more that stock timing. Reeds will help a bit but not much. An earlier set of heads will help but then an engine that I feel should be run on 91 octane will need even better fuel, less timing and bigger jets.

[MrG]

You can take the exhaust tuner off and clean up the flow where the exhaust is routed back to the Bottem web. the factory just milled out the web with a plunge cut circle leaving a big U that needs to be turned upside down . a big difference in flow is allowed as well as tuning in the exhaust shockwave the Bottem has one water passage for the bubble jacket so the web ends up being a rounded relief !! You can do a flat out run before and aft the mods and tell us the results. !!!

[MrG]

If it’s not a bubble back I have the stuffers gaskets an tuner I did to my 89 115 and had a spare set still on shelf I’d sell off now that I’m doing a 3,3 monster

[Merc 2.5]

I appreciate all responses, not sure how far the guy wants me to take it ? He called 1st time and wants a tune up ,but I immediately start thinking more power , bit this guy has 0 experience with outboards, I believe this is his 1st true boat with more than a 40 or 50 hp. I think we will just do a tune up and let her ride. So I'm guessing it's nothin like a merc , where u can set timing where u want it , without lectrics bringing it up and down when it wants to ?

[MrG]

It will make it have power and fuel efficiency increase I have noticed a stock one just makes more noise between 3/4= wfo but after just tuner you feel the acceleration from 3/4 on I’ve done many mods just for this over the past first one I did was back in79 85 javelin on 17 Seacraft went from 44 mph to 56 then switched to 1 3/8 carbs then we were in the 60s spedo was pegging out was fun back then running thru the cut and penny camp tolitseat ally nest key all before the restrictions like now

[Merc 2.5]

What kinda plugs do these motors like ? I'm a merc guy. Just helping buddies

For sum reason I'm thinking champions

[MrG]

NGK BUHW same Merc plug works great

[MrG]

Stock were UL77V champions

[racer]

Actually factory says QL77JC4 for plugs

[Merc 2.5]

Actually factory says QL77JC4 for plugs

Racer. U think I'd be better off putting the champions back in it ?

[racer]

IMO yes champion in an OMC and NGK in most Mercury.

[MrG]

I’ve been running the ngk BUHW for 25 years and never had a plug go bad but can’t say the same for champion I don’t change them till they start to rust on the outside I remember back in the 90’s I was cured from running champions when I lost a 1/2 mile run because of a bad champion plug there quality was not constant for me and in not in on the Denso price for plugs yet and those Opti / Rude 20 dollar plugs hi priced champions ouch but I do want the plasma spark of the Rude burnt up my spark checker back in the day so now just carb plugs NGK BUHW no fowling and Lill more compression without all that Standard plug opening that’s my 35 years of Sparky’s Oh also for them IO guys who know them big blocks always Fouled plugs they were Delco GM and champions but when you went to a NGKYR5 no more issues that’s my experience wrenching