Engine "flat" when idling/exiting launch

[byebye]

Hi Guys, I use my 2004 sportster 4tec 155hp (single engine) only about 5 times a year (wife/kids/job).

When exiting the boat launch I have to go very slowly, in forward at idle speed.

I noticed last weekend the motor sounded really flat & rough at idle, like it had gotten loose on it's mount. Checked but looked fine.

Once clear of the launch, at cruising speed the motor would change pitch (slower/faster/slower).

When leaving the beach about a hour later, I ran it full speed for a few minutes (waves were down at this point) and problems seemed to be gone.

When entering the boat launch again at trolling speed to go home, the engine sounded fine.

So basically running it at full speed for awhile seemed to make the problem go away.

WTF???

 

[LouDoo]

I'm not an expert on 4-tecs, but it sounds like it could be something simple like the spark plugs.

Lou

 

[pwgsx]

Change plugs first...... Could be clogged injectors, bad coil packs OR idle control valve is bad OR TPS is bad or needs to be reset to 0 by the dealer.

 

[byebye]

Thanks guys, changing a plug is something I can do. My research says NGK DCP-R8E.

I'm not sure the plugs have *ever* been changed, boat is an 04 with (I'm guessing) 75 hours.

Since I often drive slowly, I guess the plugs could be fouled, or is that urban myth? My brother always gave me that excuse for driving our old snowmobile really fast "gotta clean the cyclinders out" lel

 

[pwgsx]

Just make sure they are the plugs with the screw off tops, the solid type wont work.

 

[byebye]

I finally replaced them - very smooth now ty

 

[James.Moon]

Even with new plugs, with my 2009 180SE 255HP, I find if I do a lot of idling along, it may sometimes be sluggish at first when going to wide open throttle. This always clears after speeding for a bit. It seems slow speeds foul the plugs a bit - the boat wants to go hard - I guess that is what it is designed to do.