carb or ignition problem?

1988 Evinrude 25hp motor.

Starts easy on 1st pull, but seems to idle a little rough. It will stay idling and idle low, but the motor seems to shake more than its supposed to. I might be wrong there, but the main problem is at WOT.

When I open it up it just flat out runs rough. Itll almost catch for a couple of seconds and sound smooth and good, then stop and cut out. It just wont stay running smooth. Its very inconsistent, last time I took it out, it ran rough just right at first, then the next 30 minutes it ran fine and sounded good.

I personally think its a carb problem and hoping it doesnt have anything to do with the ignition components, but who knows. What could this problem be that I might be missing.

ps. I am ordering a carb kit and going to install it soon.

Re: carb or ignition problem?

Good start. Look for a saturated float while you're in there. The float will not come with the kit.

Re: carb or ignition problem?

Do a spark test as well just to rule out ignition. See if each plug will jump a 7/16 gap with a strong blue spark. Use a spark tester for this. It's an easy test and do it when the motor is cold then warm.

MAS

Re: carb or ignition problem?

will do and update with the results...I know the spark is good and blue when cold, but I havent checked it after the engine being warm.

Matt

Re: carb or ignition problem?

it is possibly carb, you have a fixed high speed jet, in the bottom of the carb bowl, that has to come out to clean, you also have a low speed adjustable jet and the top of the throttle body. here is how to clean the carb, properly. and adjustments for the low speed needle. if you have problems after ward. you could have a coil going bad and not firing.

carb cleaning: http://forums.iboats.com/showthread.php?t=244013

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

Re: carb or ignition problem?

I have always wondered why the high speed jet is supposed to come out to clean. I can see it...If I shine a light down there, I can see straight through it plain as day. If their were any spec of dirt, I would be able to see it. Unless there is something else you guys are talking about.

The carb looks clean, but I am going to clean it again and do a carb kit.

thanks for you guys' input. Any more input will be appreciated...could a powerpack cause something like t his at WOT?

Re: carb or ignition problem?

A spark test eliminates power pack, coil, plug wire etc.
Sorting out the difference between ignition and fuel delivery is easy if you do the spark tests first.

Re: carb or ignition problem?

Would I be able to visually see an intermittent spark...Like when I pull the cord, if it sparked sometimes and sometimes not, is it easy to tell that visually?

Are there any examples of a homemade one?

The only way I have spark tested it before is when I got it, I just pulled the plugs and had them against the metal of the powerhead and the spark was jumping all around.

thanks

Re: carb or ignition problem?

spark testers cost about $10 at any auto parts shop, set the gat to just under 1/2 inch (7/16) , a spark plug won't work, you need that big gap.