1997 Mercury 90HP 2 Stroke O/B

[cc190cc]

Greetings,

I have a 1997 Merc 90hp 2 stroke. I purchased last year and do not know to much about the motors maint. history. The engine runs a little rough at idle and tends to start smoking alot after about 30 min of low rpm use, like if im trolling. I noticed when i first start the engine it runs super smooth for about 5 seconds than starts to run a bit rough, almost like its loading up. Can anyone tell me if they have ran into this issue. Ive noticed a couple of times when coming up on plane the boat will slightly hesitate than its fine. It really screams and runs well at high RPM's. Do i need to adjust carbs, if so is there any info on here as to the procedure. Im pretty technicially savvy just have never messed with carbs on one of these.

Chad

 

[cc190cc]

Re: 1997 Mercury 90HP 2 Stroke O/B

Come one guys, can anyone help me out. I know people have been very helpful in the restoration threads when i restored this boat. If the right answer is to bring it to an authorized Merc dealer that is fine.

Chad

 

[saumon]

Re: 1997 Mercury 90HP 2 Stroke O/B

In a case of an engine of unknown history, never assume anything and the more efficient approach was to check, IN THAT ORDER, for:

1- good, even compression on all cylinders (over 100 psi and within 10%)
2- strong (blue, crisp) spark at all cylinders (jump at least a 7/16 gap)
3- fuel system checkup (from the tank pickup up to the carbs with everything between, including the fuel lines, the primer bulb and the fuel pump)

So, if compression and spark test ok, i'd clean and rebuild the carbs and fuel pump...an easy job to do. You'll waste your time trying to adjust a dirty carb!

Here's the OEM shop manual: http://rapidshare.com/files/213240343/75-90-100-115-125.rar

password is ?ribforum?

 

[Jacket4life]

Re: 1997 Mercury 90HP 2 Stroke O/B

Hey saumon, you got a link like that to the older Merc's??? I have a 73 MErc 500 (50HP), I'd love an online resource like that!

 

[saumon]

Re: 1997 Mercury 90HP 2 Stroke O/B

Hey saumon, you got a link like that to the older Merc's??? I have a 73 MErc 500 (50HP), I'd love an online resource like that!

Sorry, but if they're available, i'm not aware of it. You'll find a ton of good info there: http://www.maxrules.com/fixoldmercindex.html

 

[cc190cc]

Re: 1997 Mercury 90HP 2 Stroke O/B

Saumon, thanks alot for the input. Im going to do a compression check. This thing starts up at the touch of the key so I was thinking that they just may need adjusting. I will start with a compression test. How can i tell if the carbs are dirty??

Chad

 

[saumon]

Re: 1997 Mercury 90HP 2 Stroke O/B

Compression tester @ 30$
http://www.pelicanparts.com/catalog/shopcart/TOOL/POR_TOOL_CAT447_pg2.htm

Spark gap tester @ 15$
http://www.pelicanparts.com/catalog/shopcart/TOOL/POR_TOOL_CAT447_pg9.htm

(those are only for reference, they're available at any auto/parts store)
Thoses are cheap but invaluable tools.

As for the carbs, there's no real way to tell if they're dirty unless you take them apart. For each engine, they sell a carb gasket kit and a carb rebuid kit. Most of the time, you can get away with only the gasket kit and a gallon of carb cleaner (you'll have enough for all your life!), unless your inlet needle is worn out, but the carb rebuilt kit is 5 times the price of the gasket kit.

For your particular engine, you'll need:

3x carb gasket kits (Mercury 13958112231 or Sierra 1872111) @ 6$/each
1x fuel pump diaphragm kit (Mercury 21857005A1 or Sierra 187817) @ 15$/each

Hope it help...

 

[mikeneal]

Re: 1997 Mercury 90HP 2 Stroke O/B

I have a similar motor 1999 90HP ELPO and they are not known to be super smooth at idle and although carbs are clean and adjusted it is tough on a 2stroke carb to idle all day happily. All that being said I would buy or download factory manual and make sure carbs are adjusted (including linkage).