2001 Johnson 50hp - Power issue

Hi,

I recently purchased a 50hp Johnson (model-J50VLSIG) and am having issues with power under load. Each of the three times I have had the motor on the water it has done basically the same thing. It starts and idles smoothly, then when put in gear has plenty of power (I have it on a Lund SSV-18) out of the hole and planing beautifully. After a minute though (without touching the throttle) the rpms drop and the motor sounds bogged down, losing all speed and power. Sometimes the rpms first fluctuate with no throttle input. When put in to neutral the motor will rev to max rpm, but won't while in gear. Once when I was on the water and the symptom appeared and I stopped and hung out on a beach for and hour or two. When I left the symptom was gone and the motor ran smoothly, but after a few minutes it returned. The last time I went out the symptom was present immediately and did not go away.

I have replaced the fuel filter, have new gas in a new tank, the valve is open and it seems to be drawing fuel fine. I have also tried choking it at high rpm (recommended by a friend to try to dislodge anything in the carbs). I now plan on rebuilding the carbs and have rebuild kits on the way.

Any ideas or advice would be greatly appreciated!

Cheers,
Sean

ps. New to outboards so I'm am a little clueless

Your friend was totally wrong about choking the motor !----------That used to be the case when motors had choke flappers.--------Your motor has a primer system !--------So cleaning the carburetors is a good step to take.-----------Hopefully no damage was done running with a plugged carburetor.----Compression test must be done.--------Good idea to install a new water pump impeller too.

Your explanation indicates that a possible fuel restriction exists, and if so, it is most likely caused by the following. This would be the very first place I'd look.

(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.

NOTE: There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

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