250 Pro XS, spark plug replacement, anything I'm missing?

[Slig]

(serial# 1B459323)
(2008 Mercury 250 Pro XS)

Symptoms: 3 weeks ago boat was running great one day, next morning it had a rough idle, coughing, shaking etc, even died a few times. Put it on the trailer and got home and pulled the thermostats and found a pretty big piece of wood in one. Figured that was it, but took it out this weekend and it idled better, but still not right. Vesselview mobile showed it's getting up to operating temp and no codes, so I ran it, and it did ok but was sluggish out of the hole and top end lacking. Was even a little hesitant to start at one point, almost like it was flooded, and seemed to smell rich. Put it back on the trailer and I'm guessing there might be a fouled plug(s)? Fingers crossed that's all it is.

Haven't owned the boat that long so not sure when it got plugs last. Per Don's previous posts (thanks Don) the proper plugs are NGK IZFR6J gapped to .042-.044 with a wire gauge tool and go no go method, thin layer of anti seize, using fuel line to prevent cross threading, then torqued to 20 ft/lbs. Am I missing anything else? Thanks

[castforcash]

Sounds like ya got it! Only thing I will add is to not pry against the center electrode of the plugs when gapping them. Use a good pair of side cutters to bend the ground electrode by gripping it from the back side.

[Slig]

Sounds like ya got it! Only thing I will add is to not pry against the center electrode of the plugs when gapping them. Use a good pair of side cutters to bend the ground electrode by gripping it from the back side.

Will do, thanks cast!

[EuropeanAM]

^^^^^

[Slig]

While I've got the lower cowling off to do the plugs, I'm going to check the water strainer as well. Thank you all!

[06 SB]

Have you checked the compressor too?

[Slig]

Have you checked the compressor too?

I haven't, how does one go about checking that? Is that something I need to add to yearly maintenance? Boat ran perfect prior to the stick in the thermostat, and after removal still have good water pressure and stream so hopefully nothing to do with the compressor.

[06 SB]

Here is a list of what Don recommends.

Recommended Annual Maintenance.

To test the compressor is really easy. Take off the belt and inspect it and replace if necessary. I normally would do a preventative replacement every 3 years. Turn the compressor flywheel with ONE hand. You should get no more than 3 revolutions before enough pressure builds up and you cannot turn it any more. If you get more than 3, it is probably toast or you have an air leak somewhere in the system. Also check the belt tensioner for it being loose or has play in the pulley. It has been a while since I had one fail but it is fairly common.

[Slig]

Here is a list of what Don recommends.

Recommended Annual Maintenance.

To test the compressor is really easy. Take off the belt and inspect it and replace if necessary. I normally would do a preventative replacement every 3 years. Turn the compressor flywheel with ONE hand. You should get no more than 3 revolutions before enough pressure builds up and you cannot turn it any more. If you get more than 3, it is probably toast or you have an air leak somewhere in the system. Also check the belt tensioner for it being loose or has play in the pulley. It has been a while since I had one fail but it is fairly common.

Thanks 06, I've got a few weeks coming up to start checking things off of this list, including testing the compressor. I appreciate it!

[Slig]

Update, changed plugs exactly as described and put some muffs on it in the driveway, and still idling rough, shaking etc and even died once. If the issue were plugs, would it have ran better immediately? As of now I'm planning to take it to a recommended merc mechanic in my area, but it'll likely be a few weeks before he can get me in.

In the meantime, is there anything else to check? 06 mentioned the compressor so that's one thing, and I found a post where Don mentioned a way to test the reeds one by one, but I can't seem to find the thread again. Sounds like it could also be a tracker valve but not sure if that's something I can check. Any suggestions appreciated. Thanks

[Slig]

Update, changed plugs exactly as described and put some muffs on it in the driveway, and still idling rough, shaking etc and even died once. If the issue were plugs, would it have ran better immediately? As of now I'm planning to take it to a recommended merc mechanic in my area, but it'll likely be a few weeks before he can get me in.

In the meantime, is there anything else to check? 06 mentioned the compressor so that's one thing, and I found a post where Don mentioned a way to test the reeds one by one, but I can't seem to find the thread again. Sounds like it could also be a tracker valve but not sure if that's something I can check. Any suggestions appreciated. Thanks

Forgot to add coil pack to that list, but seems a spark plug tester doesn't always find the culprit. I don't want to start throwing parts at it but would be willing to buy 1 coil pack and swapping until I found it, if that's a possible solution.

[JOE54]

tracker = start up engine ,breif time kill it and depress schrader valve on port side any fuel or vapors can be a good test for leaky tracker valve as well as other diaphrams in rails

[Slig]

tracker = start up engine ,breif time kill it and depress schrader valve on port side any fuel or vapors can be a good test for leaky tracker valve as well as other diaphrams in rails

Got it, thanks Joe, preciate the info and suggestion.

[Slig]

tracker = start up engine ,breif time kill it and depress schrader valve on port side any fuel or vapors can be a good test for leaky tracker valve as well as other diaphrams in rails

Quick update for anyone else with a rough idle and listed symptoms: After crossing off plugs, coil packs, thermostats, etc. as the culprit I ended up taking the boat in. Turned out to be a diaphragm as Joe suggested. Went ahead and had them replace all 3 and they are not cheap little parts. One thing to note, the place I took it to had 2 of 3 in stock but were waiting on one to ship(part #804533), and that shipping date came and went. I ended up calling around and found one myself at a local boat dealer. So if you are in this situation awaiting parts, you might ask if you can get an OEM one yourself and bring it in. Then see if Don has it, or someone else close by, seemed to save me some time.

[JOE54]

[EuropeanAM]

Another note I would make: I don't normally recommend replacing other diaphragms "just because you can". Replace any bad or compromised ones- if there is nothing wrong with the ones in the engine, there is really no benefit in replacing (new or old are BOTH subject to failure potential).