1999 25hp Johnson Just Plain Slow

[wpguillot]

I have a 1999 25hp Johnson on a 14x48 Lowe Big John. The motor has had a number of repairs lately, but I still don't believe I am getting peak performance. The fuel pump and head gasket have been replaced. Carburetor and tank cleaned and reset. Link and sync completed, which helped quite a bit, and engine raised to proper height. After all of this I am still getting only 16.2 mph at WOT with just my girlfriend and I (320 lbs, I am 200 of that, just to hedge against anyone with too much wit) and a trolling motor and battery. I have replaced the plugs and after running today for a while, they seemed a little sooty, but the end that is supposed to be tan was. I am about at the end of my rope, looking for any advice or should I just expect to be this slow. I have seen and read about so much more performance out of a 25hp. Thanks

 

[fireman57]

Re: 1999 25hp Johnson Just Plain Slow

My '91 25 pushed that same size boat about 30mph. Scared me to death. Check your compression first and make sure you have the same in both cylinders within 10% of each other. Make sure you are using the correct plugs. If it seems to bog then I would take a timing light with me and make sure that both wires have spark. Could be a weak or intermittent coil breaking down. Get some seafoam and do a decarb. Do a search on decarb and you will get all the info you need.

 

[wpguillot]

Re: 1999 25hp Johnson Just Plain Slow

Thanks fireman. Come on guys, I know yall have some more ideas. This boat is really starting to drive me crazy. I know it can perform better than this. HELP!

 

[fireman57]

Re: 1999 25hp Johnson Just Plain Slow

I suppose that you have tried trimming the engine in or out more for optimum push. Also make sure that your fins on your engine are even with the bottom of your boat for starters. you may have too much engine drag.