Mercruiser 3.0 Idle Spring

[Jonness]

I have a 1997 Mercruiser 3.0 LX with the Mercarb carburetor with the single idle mixture adjustment screw. The boat runs perfect once adjusted, but after a half hour cruise at 25 knots, the idle mixture screw back out enough to make the boat idle rough. I've had the boat since 100 hours, and it's been this way since I got it. The spring on the idle mixture adjustment screw appears to be the stock spring and appears to be firm enough to hold the screw in position. But it doesn't.

Has anyone else had a similar issue? And if so, is there a part number for a heavier spring or something else you done to fix the problem? I'm thinking maybe putting a couple of washers on the screw to compress the spring a bit more might help, but a heavier spring seems like it would work better.

Thanks,

Jonness

 

[Bondo]

Ayuh,.... Why not just S t r e t c h out the spring ya got,..??

It'll do the job yer lookin' for,.....

 

[Rick Stephens]

Try Vibra-Tite on the threads. Vibra-Tite is not a 'thread locker' glue like Lock-tite, but a super high viscosity solution to screws loosening. It doesn't glue it in, it just adds measurable resistance to turning.

When you use it, paint it on the threads and let sit until dry. Then set your mixture and forget it. If you have to change the setting, just do it. It won't turn quite as easily, but no where near the danger point where you might break a screw or bolt.

I have been using Vibra-Tite on all my steel into aluminum bolts and screws for a long time in my welding shop. Last few years used it on every bolt or screw on my boat going into aluminum. Keeps electrolysis down and makes them a lot easier to get out later. I was having trouble with the screws in my steel roof working out because of temperature based expansion and contraction of the panels. Vibra-Tite on the screws pretty much fixed that problem. I tried 5200 and instead of backing out the roofing screws would just shear off.

Rick

 

[Jonness]

Thanks for the tip Rick. I ordered some Vibra-tite from Amazon, and I will give it a try.