1993 48 hp evinrude surges/hesitates randomly

[Todd Klatt]

Hello

I am having a problem with my 1993 evinrude 48 HP. The engine will start/idle fine when I put it in the water. It will run well initially on a plane/full speed but almost without fail will start surging, this is the best word I can think of to describe it. It will very quickly and dramatically lose power, then try to regain power then lose power ect.... When this happens I wil bring to idle and it will still idle fine and when I put it back in gear will run fine at trolling speed but as I bring it up past idle/trolling speed the problem will happen again. (I dont have a tachometer, so I cant give you the RPM's that the problem is occuring at). The thing is, it doesnt happen every time I have it on the water, nor does it happen at a specific timeframe, sometimes it happens after running for an hour, sometimes 15 minutes, its very random. The engine sat for about six months, before I put it back in the water about a month ago. I just had the carbs cleaned and rebuilt. I have also replaced the gas tank/line. I also have been using and additive in the gas, which is suposed to counter act the effects of ethanol. Not sure where to go from here, any ideas would be greatly appreciated.

 

[Joe Reeves]

Re: 1993 48 hp evinrude surges/hesitates randomly

If the engine acts similar to running out of gas temporarily, I would suspect a fuel restriction problem. Usually this is due to a sticking Anti Siphon valve. See the following.

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

If on the other hand, the surge is a instantenous drop and raise in rpms, that usually indicates an ignition problem. As such, you would want to check the spark on the engine when this problem pops up..... as follows.

Remove spark plugs, hook up a spark tester whereas you can set a 7/16" gap. The spark should jump that gap with a strong blue lightning like flame.... a real SNAP! Note that using spark plugs to test the spark is a waste of time..... the 7/16" gap is important. A spark tester can usually be found in any automotive parts type store.

Describe the appearance of the spark plugs.

 

[Todd Klatt]

Re: 1993 48 hp evinrude surges/hesitates randomly

J. Reeves,

Thanks for the suggestions. I failed to mention it before, I did change the spark plugs as well, about a week ago. The old ones had what looked like oil on the threads, and the gaps were much greater than what was recommended. After I changed the plugs the engine seemed to run a little smoother than before but the above problem persisted. I will however check the anti-siphon valave and the spark as suggested and reply with the results, thanks again.

 

[fireman57]

Re: 1993 48 hp evinrude surges/hesitates randomly

You also might want to check your tank/engine fittings. Sounds like an air leak to me.

 

[Todd Klatt]

Re: 1993 48 hp evinrude surges/hesitates randomly

Fireman57 thanks for the suggestion I give that a shot