Excessive smoking at idle.

'94 Mercury 60 HP tracker, 2 cycle on 17 ft aluminum boat. Last few outings, I noticed that engine smoked noticeably more than in past at idle. I checked the idle screws setting, (1.5 turns out). I thought maybe the one of the carb floats may be stuck but I'm not sure. This happens when motor is at lowest position on transom stop. If I bump the motor trim up slightly it reduces the smoking but I never used to have to do this. Motor stop position is never been changed. I have rebuilt the carbs twice in the past and I take pains to make sure the floats are set level to casting, (as described by many of the experts on this site). Today for an experiment, I bypassed the auto oil feature and ran from a gallon container mixed at precisely 50:1, (still smoked excessively). Before I tear into the carbs again, I thought I would post this just in case I missed something else. Also, I did notice that when I had reconnected the auto oil pump and waited for the oil to be flowing again at the plastic Tee fitting that there was some inconsistency of gas flowing into the fuel pump. I could see what looked like air bubbles or voids at this point. My question on this issue is the gas line supposed to full at this point of mixing with the oil just in front of the fuel pump? May not be an issue but I thought that I would ask. In the winter, I treat gas with Sta-bil and I only run 90 octane alcohol free gas. I would appreciate any opinions or suggestions.

check for air leaks on entire fuel system from tank to carbs. Check the fuel pump diaphragm.

That "1 1/2 turns" idle adjustment is preliminary only. You need to fine tune each carb with the boat on a trailer or tied to a dock (so it won't trick you).

Jeff

Thanks, I will do this.

Thanks, I am going to replace the old fuel hose. Also, is there any need to check inside the tank for any potential leak source?

I had a '94 and a '00 60 hp. You say it smokes excessively at idle. Well the injector pump mixes at about 100:1 at idle.

now you premixed 50:1 out of a gas can. The motor is going to smoke
a lot more at 50:1 then it will with the injection hooked up. This is not a good test to troubleshoot IMO.

Sometimes the check valve in the oil line goes bad and it will gravity feed too much oil into the engine. I would check the check valve and see what you get.

Good point. I should be able to disconnect the oil output past the check valve with engine off to determine if it is seeping past. Thanks for the input.

unclebob said:

Good point. I should be able to disconnect the oil output past the check valve with engine off to determine if it is seeping past. Thanks for the input.

Click to expand...

sure thing

Yes you can disconnect it and put it into a 20oz bottle and let it set overnight to see how much oil collects. I think that valve is only rated at 2psi which basically just prevents the oil from gravity feeding. While you are in there you can make sure the oil pump hasn't come loose from the block. When I serviced mine I went ahead and removed the lower cowl. Much easier that way.

Thanks for the suggestion. I will run this test tonight and see if anything seeps out. I wouldn't have thought of this but it seems worth while to be sure. Thanks for the idea.

That check valve going bad is the #1 reason for over oiling in these engines.

Update - Problem fixed, replaced all hoses, clamps, check valve, primer bulb from tank to fuel pump. Also, installed fuel pump repair kit. No more excessive smoking. The root cause turned out to be the zip clamps that were used to secure the gas hose to fittings. It seemed this was where the air was being sucked into the gas line when running. Using a clear vinyl hose made it easy to locate the sources, (which were several). I replaced all the clamps with the screw type band type which totally eliminated the problem. Also, there was a problem with this engine which was my first posting on this forum two years ago. When the engine was shut off for an extended period of running, it would be a little difficulty in restarting. Had to choke to restart. This has totally disappeared and now starts immediately in all conditions. Maybe it was vapor locking, there was a lot of air being taken in while running. Anyhow, I want to thank all the contributors for their advice as it enabled me to fix my problem.