Mariner 90 3 cyl couple questions

[junkyardwarrior]

1987 model I believe (serial 0B132734)....

Starts ok but will run on one cylinder for a while, then it will take off & run on all 3. Seems to be worse in cooler weather. Sometimes during the summer it would run fine. Seems to only do it when the engine is first started-after it is run for a while, it will start & run every time on all 3 cyl. DOes this sound like a switchbox going south?


Also-I can't get it to idle down below 1300 RPM. Manual says 700 I believe? I have adjusted the carb every which way from Sunday and I can't ever get it down that low. Always wants to die? Any ideas?

Last question-I need a water pump. It works but pressure is getting low (~5psi wide open, used to be 10-12). It's been a while since it was replaced. Based on my serial number, I can't find complete kit (housing and all). Does anyone know where I can find one?

Last question-how much does this motor weigh? I have my eyes on a new 90 HP Yamaha and I didn't know how much weight difference there is--if any.

Motor is mounted to a '87 model Tidecraft bass boat-I like the boat (too small but I still like it) but this motor is just giving me fits.

 

[Silvertip]

Re: Mariner 90 3 cyl couple questions

Your best source of parts when you can't find what you are looking for is your local Mercury dealer. As for the cold running issue, have you looked at or replaced the spark plugs?

 

[Chris1956]

Re: Mariner 90 3 cyl couple questions

You may look up the weight at the NADA site. Idle speed is mostly controlled by idle spark timing. It sounds like you need to do a link and synch on that motor.

You can replace just the impeller, the impeller and upper water pump, the impeller and waterpump base, however, I do not think there are kits with all three pieces. Normally you would replace only the impeller. If the upper housing is cracked or the liner is worn, replace it as well. It water is leaking into the gearcase, replace the waterpump base and impeller. Use new gaskets and orings and a new wearplate, for best results. these are all included in the impeller kit.

 

[electricjohn]

Re: Mariner 90 3 cyl couple questions

Motor wieghts 294 lbs. (ELPTO)

 

[junkyardwarrior]

Re: Mariner 90 3 cyl couple questions

I have looked at Southern Marine's catalog at work (we are a dealer) and they list a couple different water pumps. So I will have to drop the foot and measure.

As far as the ignition, yeah I have replaced the spark plugs already. I seem to remember seeing a replacement plug for the gapless plugs that the manual calls for. Anyone ever hear of this? It's definitely an ign problem, but I don't have a lot of experience in Mercs. I've sold/worked with Yamahas for the last 15 years. The switch box--I could tap on it a little and it seemed to take off & run ok. I guess that means that the swtich box is going south. Only problem is, Southern Marine shows a bunch of different switchboxes-and none of them list my serial number in the ranges. Skips over. They are Sierra switchboxes.

The idle issue...I spent most of the day one day last week messing with it and no matter what I did, I could not get it to idle down in neutral and it still hold an idle in gear. Are there any links that will help show how to a link-n-sync? I remember seeing something once before, but it dealt with a tower of power inline 6 merc...which used a little bit different linkage than my lowly 3 cyl.

 

[junkyardwarrior]

Re: Mariner 90 3 cyl couple questions

Alright I think I got it!

I was out messing with the water pump earlier and decided to test run it in a tank after I put the foot back on. After I fired it up, it was again running on 1 cylinder. So I pulled the cover off of the igntion components and noticed that one wire that goes to the switch box was broken-corroded and broken. It was a white/black wire on the bottom right side of the switchbox. I got a piece of wire and repaired the break, and upon starting the motor it ran perfect. I then did a link-n-sync, the best I could...got the idle down to 850 in neutral and about 750-800 in gear. Probably could go lower if I wanted. As the timing is advancing just past TDC, the throttle is JUST being opened on the carbs, so it appears that I've gotten it at least somewhat correct. I set the WOT timing at 28 deg BTDC, and achieved best neutral slow idle at 4 ATDC.

So if anyone else runs into problems like that, have a look at the wiring. Thanks for everyone's help. Now, off to find me some kind of inexpensive jack plate.

 

[Chris1956]

Re: Mariner 90 3 cyl couple questions

Are those the correct max and idle timing specs? If you are not sure, doublecheck them. Today's rotten fuel is hard on motors that are set with too much spark advance

 

[junkyardwarrior]

Re: Mariner 90 3 cyl couple questions

Yes. I am looking at the manual right now (OE Mariner manual on Fiche...LOL). Actually it says max cranking advance is 32 BTDC, running 26 BTDC. So it' right there. Actually mine is a degree or two under the spec-I left it that way "just in case" there was a chance of picking up some cat-pee fuel. I may just up it to 32 cranking just so I know it's right where it should be.

 

[junkyardwarrior]

Re: Mariner 90 3 cyl couple questions

One more question:

Does anyone know where I can pick up a cheap water pressure gauge? I have the tubing and everything else, but I don't have a gauge (in-dash).