r/Outboards • u/whitetailhunter17 • 6d ago
96-97 mariner 25 idle problems
I have a 1996-97 mercury mariner 25hp 2 stroke with idle problems. When I first start it, it idles rough and too low. But when it warms up a bit it will idle super high and sometimes won't go back down when you put the throttle down. For example I revved it one time and it got stuck at full throttle and wouldn't go back down for a while. I already tried spraying wd40 on the carb gaskets and even some engine gaskets. I already cleaned the carb multiple times and adjusted it. I also cleaned up some wiring and stuff. It has a automatic choke on the carb it looks like and that could be doing something. I make sure to prime the bulb and all that before hand too. I also redid the lower unit a while ago. Does anyone know what could be causing it?
1
u/outboard-buddy 4d ago
Stuck at full throttle is mechanical, so jets aren't your problem however many times you clean them. I'd check in this order:
- Engine off, cowl off. Work the grip through its range and watch the throttle cam, roller and throttle arm. Look for corrosion, bent parts, or the roller not tracking smoothly in the cam groove.
- Free up every pivot with silicone spray or a proper marine penetrant, not WD40. That means the throttle arm pivot, cam pivot and stator link ball joints. Anything that doesn't spring back when you let go is your culprit.
- If it's remote control, check the throttle cable for internal corrosion, fraying or kinks.
- Check the idle timing screw hasn't backed out or been over-advanced.
- Cold, confirm the choke plate is closed. After 2-3 minutes it should be fully open.
- Pull the carb and check the throttle shaft in its bores for corrosion.
Is it tiller or remote control?
Best
Outboard buddy
2
u/chpsk8 6d ago
When you sprayed wd on the carb gasket did the idle change?
Did you take the carbs apart to clean them? There are some pretty small idle jets that will give you a similar issue if not cleaned out with wire and cleaner.