1997 Evinrude 25hp fluctuating idle and small backfire from upper exhaust

[WhiteRice]

Well, got my "new to me" boat out today after tinkering with it over the last 2 weeks. Changed the gear oil, impeller, thermostat, fuel filter and ran a can of SeaFoam through the gas tank. Today it started fine when I put in but after about 20 minutes, the idle began to fluctuate (RPMs raising then lowering) and I would get an occasional back-fire about every 1-2 minutes (I say back-fire but it was much quieter and released a larger "puff" of smoke from the upper exhaust. The motor would not go above about 10mph and stalled on me a few times when I tried to throttle it up. Had a hard time trying to get it restarted (pull start BTW) but when I did, it would not go above 10mph again and I limped back into the dock. Came home and fired it up in the barrel to flush it and it ran fine at med idle but still fluctuated with the occasional "puff".

From what I've read, it may be a carb issue but I am still learning outboards and my not want to tackle cleaning three carbs. How easy is this to do or would I be better off letting a shop take care of it? Is there something else I should be looking into from a trouble-shooting aspect? I want to learn as much as I can so I can take care of things myself but with it being 98 everyday, it gets a little annoying trying to trouble-shoot outside. Thanks in advance!

 

[jbuote]

Cleaning the carbs is really pretty easy.. Not that many parts involved really, and it's mostly just making sure all passages are clean and not obstructed,
​Basically, take it apart, soak the non plastic parts in cleaner, blow them out with compressed air, and reassemble with new gaskets, seals, float needle etc.. Pretty much everything that comes in a carb rebuild kit. (You'd need 3)..
​
​Quite sure somebody here can help step by step for your specific carbs, but that's the "Basic" gist of it..
​I bet you could do it no problem.. All 3 carbs should be virtually identical, so if you can do 1, then 3 is no issue..

Hope it helps..

 

[racerone]

Is the oil injection / mixer unit in service on this motor, yes or no ?---10 mph at max throttle ?-----What kind of boat ?-----Mixing gas oil at 50:1 on it ?

 

[WhiteRice]

There is no oil injection system with this motor. This is on a Carolina Skiff J16 and the max speed I could estimate was about 10mph. The RPMs were no where near enough power to propel the boat any faster so I don't feel it was an issue of "non-planing" since there was not enough power. The mix was 50:1 on a fresh tank today with stabilizer.


Thanks Jbuote. I may read through a few more topics and do some searching on YouTube. I'm sure it could be done... Just tired of sweating my ss off in the garage. lol

 

[jbuote]

^^ LOL.. I took mine off, and did it in my basement.. Had a fan in the basement window for exhaust, so I didn't fumigate myself, but it worked.. hehe..

 

[jbuote]

Sent a PM...

 

[oldboat1]

Stabilizer or Sea Foam? Running a decarb agent from the tank can loosen up nasties in there for use by the motor (and doesn't do much to clean up the carbs).

Have you tried using the primer bulb when the motor acts up? (potential fuel pump issues). Rpm fluctuation may mean some lean running (lean/rich fluctuation), with could be a fuel pump issue or a seal leak. You could spray a little carb cleaner around the base of the powerhead and see if you get a change in rpms. It would also be a good idea to do a baseline compression check. If a PO overheated it, a head gasket might be in order.

 

[WhiteRice]

Oldboat1: I actually cleaned the tank out with SeaFoam (saw a vid on pouring some in there when empty to let it sit and then slosh it around and pour it out. I did that and a few particles came out with it, but nothing crazy). I followed the video from the SeaFoam YouTube channel about putting a can in the tank and though it would do some good as the video stated. I did not try squeezing the primer bulb when the idle drops. I may give that a try as well. Thanks

 

[racerone]

Do a compression test on this motor.---Check for spark on all 3 leads.----Low speed needles may need to be adjusted.---On most motors they are set with " turns out from seated " but not these 3 cylinders motors.----Have a number of these motors that are for rebuild / parts.-----Electric start / remote or manual tiller model ?

 

[WhiteRice]

Do a compression test on this motor.---Check for spark on all 3 leads.----Low speed needles may need to be adjusted.---On most motors they are set with " turns out from seated " but not these 3 cylinders motors.----Have a number of these motors that are for rebuild / parts.-----Electric start / remote or manual tiller model ?

Pull start with remote. Is there a good / easy way to check for spark on a pull start when you are working solo?

 

[racerone]

Sure---Make something up with some wire and carboard / plywood.--Glue / staple / tie wire to the carboard with 3/8" gap between the ends.-Make wires long enuff so that you can see the gap and clip one end to the block and stick other end in sparkplug boot.

 

[oldboat1]

or get an adjustable spark tester from an auto parts store ($10 or so). Remove plugs and test each lead. Trick is to arrange the tester so you can see it while pulling over the engine (extending the ground can help). Pull it over three or four times and check.

 

[racerone]

There are 3 o-rings on the cylinder head.---No head gasket !!