Runs rough at idle

[ronjon444]

I recently purchased a 1981 Sea Ray 25' with a 260 Merc. The motor runs good above 900-1000 rpms. The motor and lower unit labors and vibrates but does not stall when I run at idle RPM's. The problem is I cannot go as slow when fishing as I would like. I have changed the fuel filter, spark plugs, condensor, rotor, cap, and points. I have also changed the lower unit lube. It was clean other than some tiny shavings on the magnet. Any recomendations appreciated.

 

[Trent]

Re: Runs rough at idle

Have you adjusted the idle mixture screws?

 

[ronjon444]

Re: Runs rough at idle

I have not adjusted anything yet.

 

[hoot]

Re: Runs rough at idle

after you get your idle set, i have seen an item that you can buy and install behind your prop. it slows your boat down by blocking the exit water. not sure what it is called.

 

[ronjon444]

Re: Runs rough at idle

I will adjust the idle mixture screws and let you know if that helps. <br /><br />I have seen a unit that looks like a retractable hydro foil that is behind the prop at trolling speeds, comes up when underway. May have to try it but I still would like a smoother idle.

 

[placebo]

Re: Runs rough at idle

Hoot, they are called Trolling Plates. Some fold down by spring tension when moving slow, then fold up when under way.

 

[trebor0301]

Re: Runs rough at idle

Sounds like the same problem I just had.I did all the things you did,but the problem did not go away.Then I realized that the boat idled a little low in nuetral(on the trailer)It dropped even more when I put it into foward.Out on the lake that low idle became worse with the prop trying to turn in the water.The torque was enough to make my boat run terrible at the lowest of speeds.Even stalling me out.I brought the tools out on the water and made an idle adjustment for nuetral to about 850 rpm.Now when I put the boat in foward the rpms drop to a little under 800.Its been running great at all speeds since.

 

[BinLurkin]

Re: Runs rough at idle

Have you checked your u-joints? I just had that problem with my 1979 Searay & that's what it was. I can get both my 260's to idle down to bout 6oo rpm & they still push the boats to fast. I haven't had much luck with trolling plates on those big engines, 350 Chev's. I think they are for outboards mostly. They didn't slow me down a knot. I still can't troll with either boat. I put the biggest trolling plate I could find on & threw over a sea anchor too. Didn't slow nothing down.

 

[ronjon444]

Re: Runs rough at idle

I will adjust the idle but I have not checked the U-Joints. The lower unit has a slight rattle at RPM's below 700. What's involved in replacing them if needed and what's a good way to verify they are wearing? The boat is not in the water all the time (trailered at the marina).