[lifeboatman3]

I have a 1994 90hp 3 cylinder Mercury and it's not performing well. It's very slow out of the hole, when it gets to top speed it not to bad but still lacks that little kick you get. Also at about 3000rpm it seems to misfire below this it's O.K and above O.K. I would be very grateful of any help.Thanks

[05GlastronSX]

just throwing out some thoughts here but it is possible that your boat is underpowered but we'd have to know what kind of boat its mounted on. Also, what prop pitch are you running on there now? maybe the bad hole shot is because the pitch is too high.

[lifeboatman3]

Thanks for the reply. It's on a Fletcher 16ft and with a 17inch pitch prop. It was running fine but now started to play up so I had the carbs cleaned and checked but no better also put new plugs in. It's hitting 5500-5800 max rpm but taking a long time to hit to the rpm. Thanks

[studlymandingo]

Is it possible you have some water in your hull or maybe some saturated floatation foam? If it performed well with the same setup before, then most likely something has changed, water is a common culprit.

[Texasmark]

I'd start with a decarb. I recently purchased an '02 3 cyl 90 and after decarbing it ran much better.On your rpm with that prop, unless your boat is REAL heavy, or the hull covered with crud, you should be running well over 6000 which is a further indication of the engine not performing correctly. That engine has a 2.3:1 gearbox so it swings a much higher pitch than a lot of engines with the more standard 2:1.I am running a 24P on that same engine on a 17' aluminum bass boat and still the rpm's are at 5600.....just to give you some idea as to where you are. But my boat only weighs 750# dry, is padded, lightly loaded, with just me.If decarbing doesn't help you should investigate a fuel starvation problem, like a clogged fuel filter somewhere in the fuel delivery line and then have the timing checked for proper advance at WOT.HTH,Mark

[lifeboatman3]

Thanks for tips. I have put a new fuel filter and lines. When I put a 19inch pitch prop on it lowers the revs still down to 4300rpm max and still slow. I put new plugs in and it went great but second time out stated to play up again so I tried another set of plugs but it didn't help?

[Texasmark]

Going to a higher pitched prop is the wrong direction till you get the engine cleaned up.It's putting more load on the engine experienced by your drop in rpm's from those you ran with the 17. After it gets to running correctly then go to another prop, if that's what you feel you need to do, but I don't have a problem with your 5800 rpm's with the 17 which would give you a much better hole than the 19.WOT operating range is 5000 to 5500 and I'd much rather be running over the high end rather than around or below the low end.If you put in new plugs andit ran great, you just ID'd your problem. Gungied plugs.So how'd they get that way? Either fouled out from too much fuel (sticking/ maladjusted float in the carbs) or the engine is carboned up.You need a decarb job......which will help free up any sticking float problems. Go to SEARCH herein and find out how to do it. Then come back and tell us what's going on.Mark

[Texasmark]

One thing I forgot, you could have problems in your fuel tank also....dirty filter (in it) or crud, moisture, rust, blobs of goo from moisture dispersants you may have put in there, bad fuel.Mark

[lifeboatman3]

Hi Thanks very much for the tips. I should have explaned better. I was running a 19inch prop last year and it was hitting 5500-5800 rpm but I want to start Wakeboarding so I got a 17 for better towing. Now with the 19 prop it's only hitting 4300 but with the 17 it hits 5500. I bought a brand new plastic fuel tank, new filter so dont think it's them. When you say decarb what do I need to do? sorry to askThanks again

[roger3645]

Go to the FAQ of the forum and read the Decarb information posted by Roscoe this should help clear things up for you. Decarb is a procedure to remove carbon build up inside the motor.