[fyshndad]

OK after nearly 1000 water miles my 1989 90HP Merc is starting to act up

I am not much of a mechanic so I am hoping to find someone here that would trade thier skills for a TUNA trip

The engine started surging at trolling speed on Sunday
it would run smooth at 7mph but when I tried getting 9mph it would act like it was choking out and then it would surge causing the speed to actually decrease instead of increasing then it would without touching the throttle smooth out and start going 11-12 mph

It was very frustrating trying to maintain a solid troll speed
the only time the engine does this is at troll speed the rest of the time it runs butter smooth

it even trolls at 2.5 mph without loading up

Anyone here that can solve my problem will get a free ride for what ever species you want to try for
I will pay for any needed parts

If anyone can give me some sugestions or ideas of what may be causing this those too would be greatly appreciated

 

[StickFish]

Hank, sounds to me like carbon build up - before you spend a chunk of change - try a shock treatment of Seafoam. I think you can get that at Napa.

 

[fyshndad]

Is that some kind of gas additive?

 

[Something Good]

I had an old 87 merc that started acting up like that at 3-4mph trolling for coho. Turned out to be the spark plugs. Might be worth a shot if it's time to replace them.

 

[dixiefisher]

Hank,
I just went through somehting similar....I have the manuals for that year, if you are inclined to tackle it yourself.....but my suggested steps.

1. seafoam first...like stickfish said napa or autozone. Using a seperate tank...pour in the 16 oz can into about 3/4 gallon of gas, and let this run for 20 minutes or so. then let the motor sit for a few. Do a second run of about 10-15 minutes or so, then let it sit overnight. A word of caution, put a bucket underneath the prop...there will be residual gunk that comes out for hours.

2. Check compression and spark on all three cylinders.

3. Check your filters and fuel lines and make sure they are in order.

4. clean out the carbs, from the sounds of it at low throttle, sounds like the jets are clogged. And from your previous motor issues, there could be some gunk that has been trapped in there.

4. This was my issue, but it was more at WOT than your low throttle. I found than my #2 ignition coil had a broken magnet....causing me to not have spark on that cylinder. I simply found this by removing the coild and looking at each one individually.

Good luck...If you want those manuals let me know and I can get them over to you...the merc manual has some decent trouble shooting steps

take care
Paul

 

[fyshndad]

I had an old 87 merc that started acting up like that at 3-4mph trolling for coho. Turned out to be the spark plugs. Might be worth a shot if it's time to replace them.

I just bought new plugs to put in it when I go down this weekend
Dang $40 for 3 plugs
I hope it is as simple as that

How often do those plugs need changing?
I do not have an hour meter but my trip log was at 988 miles when I got in on Sunday

 

[Ride Red]

I'd be concerned if you found someone to work on your motor, but they decline the tuna trip. Have them commit to the tuna trip first.:jester:

 

[Chrome Bumper]

We have a pair of merc 150's in the stable now. I also would like to hear of good mechanics near NW Portland.

Fyshndad, I'd soak it in seafoam, in the cylinders and carbs/bowls, check for water in the bowls and plugged filters, and put in new plugs. You can do that at home and maybe save a trip to the shop.

The directions are on the cans. Some you spray in the carbs while running to hit the cylinders, some you add to a small gas can and run through the carbs and into the engine.

You do it in the drive way.

 

[Something Good]

If you're using an engine with a carb for trolling I would change them every year. I already had to have my 1 year old T-8 Yamaha tuned up and the carb had to be taken apart and cleaned out because it was running poorly.

 

[Chrome Bumper]

2 strokes need their plugs changed all the time. Synthetic oil seem to burn cleaner. That's my story and I'm sticking to it.

If you premix and don't run close to WOT often I would go leaner than 50:1 on the mix.

100 hours is plenty time to foul a plug. Even on a 4 stroke if you troll alot.

$13 a plug? Ouch!

 

[Han Solo]

Hank I had some issues with my outboard this year. It came down to garbage from the fuel and the effects from that on the carb.

The motor in question is a T25 4 stroke Yamaha. Only a few years old so I had some trouble believing I needed a carb rebuild. But I took off the carb and used the soak in the can carb cleaner you get at napa in the gallon can.

You remove all plastic, rubber and so on before soaking. And get a reseal/gasket kit first as this stuff eats anything that is not metal. Before the carb cleaning it would not idle or run at any constant speed other than wide open.

After cleaning it is like a new motor. So my new routine is to run the fuel out of the motor after every use. It seems like if it sits in the motor for more than a week or two I have issues.

BTW a timing light used on each plug wire while the motor is running will tell you if your plugs are working without taking anything apart. A steady rate of flash on the light and all is ok if it flickers or is intermittent you have issues with spark on that cylinder.

The other thing is if you premix .. buy a ratio rite and mix the oil exactly at the correct ratio. More problems than you can shake a stick at with 2 stroke mixed by guesswork.

Good luck.

 

[fyshndad]

Hank I had some issues with my outboard this year. It came down to garbage from the fuel and the effects from that on the carb.


The other thing is if you premix .. buy a ratio rite and mix the oil exactly at the correct ratio. More problems than you can shake a stick at with 2 stroke mixed by guesswork.

Good luck.

This motor has an oil tank bolted to the engine that mixes the oil so I do not have to measure it

I am starting to believe that I need to rebuild the carbs and replace some hoses with ones that are not affected by alcohol

Paul I would like to borrow that manual sending you a PM

Thanks for all the opinions they all sound like good reasonable advice

 

[Chrome Bumper]

A lot of mechanics dump the auto oiler. If they quit working right they can fry your motor before you know what's up. A motor going on 20 years old has got to have some crud build up in the carbs, seafoam might get it, a rebuild definitely will.
Even new plugs can quit kicking on you. If you take them out, then lay them on the engine and crank the motor you should see pretty blue sparks on all of them.

 

[Moldy45]

I would give the seafoam a try Hank.you can do this right at home. I have used it on my motor with great results.Like was mentioned use a bottle in a portable with just a gallon of gas and let it run at idle for 15 mins then let it sit for a good 30 mins then start it and run at idle again then let it sit ,repete this 2 to 3 times. you will be amazed how much carbon will burn out

 

[Salty Walty]

Hank,

There is some good advice here fromthe dogs. Give the Boat doc a try too.

http://www.ifish.net/board/showthread.php?p=1631741#post1631741

Good luck with your engine.

 

[HntnFsh]

Buy your plugs at Carquest,Napa, or some place of the sort.My guess is you could cut the price to less than 1/2 of what they cost at a Merc dealer.

For my SJ and my 115 it was closer to a 1/3 or 1/4 the cost for the exact same plug.

HntnFsh