Engine problems of my own

[Gumby]

Was cruising across the lake into 20-25 mph winds at 3/4 throttle, everything running fine. All of a sudden the rpm's drop to about 1/2 to a 1/3, but the motor never got rough or died. Brought the throttle back to nuetral and tried to take off again. As the rpm's came up and the boat got moving, the rpm's again dropped off and would not come up to full power. Motor is '93 Merc 50hp w/Quicksilver throttle. Have checked all 3 plugs, look uniform and pretty good. Could the problem be with fuel delivery? Don't fully understand 2 stroke motors, so I didn't take too much apart. Just looking for some in-sight as to what the problem may be. Talked to some reputable mechanics, all said they couldn't diagnose problem over the phone, and all are backed up a week or more. Looking for any help to fix the problem, although wife would love to have me home for a few weekends to do "honey-do" lists. Please, spare me from the chore list!

[Hans]

Could be a fuel delivery problem (in fact, probably is).

Check your fuel filter... make sure the primer bulb isn't collapsed .... look for kink in fuel hose .... is your fuel tank venting OK?

There's a few simple things to check.

Hans

[Don]

Maybe your fuel pump is going bad.Take your boat out once more and try it,when it starts to bog down squeeze the primer bulb a little and see what happens.If it picks up and seems to run fine when you do that ,it is more than likely a fuel pump going bad.

[Bear]

Change your plugs, looking at them will not tell you a the time if they are bad. Been there done that.

Bear

[WalleyeGuy]

Gumby,
I had a similar problem on a 1998 150 Optimax. Although our motor's are considerably different, I can offer my experience. I had the same situation on the Illinois River one weekend. I was moving along at 45 MPH when the motor dropped to below 2000 RPMs, but it was running smooth and never died. Unfortunately, it would never get over 2000 RPMs for the rest of the day. I later found out that my alternator was shot, and the motor was limiting my speed because of low voltage (battery dropped below 10.5V). Once the alternator was replaced, never had a problem again. I've heard that people have had problems with their batteries, and once replaced the problem is fixed. Make sure you are getting enough voltage out of your battery. It may be as simple as that. Good luck and tight lines.

WalleyeGuy

[Eyez]

I'm not sure if a 1993 50hp is capable of rev limiting itself like that. Opti's are highly computer controlled, and that sort of behavior is one of the "features" :) I would lean more towards the fuel delivery explanation. change your fuel filter, see if the bulb is collapsing when it bogs, if it's not, try squeezing it when it bogs as mentioned above.


Eyez

[Hairy Minnow]

I had a similar incident; motor running full throttle, then drops to 1/2 or 1/4 throttle. Turned out to be a bad coil. This was on a 1995, 75hp merc. Just something to consider.

[EAGLE EYES]

It sounds to me like Walleye Guy is on it. Check out your battery, it might not be puttin out enough DC. A bad battery with low voltage, will cause this problem on any size motor that contains a CDI box. Low voltage won't allow fast enough spark delivery, thus causing the short revolutions you are seeing. If your battery is good, then try looking at fuel delivery. Good luck! EE

[RANGER]

I agree with all the probable causes represented here. There are any number of solutions. I'll offer one from my own files - 1982 70hp Evinrude, did the same thing and drove me bonkers for four days. I was shooting ever possible trouble-causing scenario I could think of. A few choice words went with the trouble-shooting. THE PROBLEM - I had a fuel tank connector with a small leak at the hose clamp that didn't show up until the demands of the engine warranted it, and then it would suck air reducing the flow. Four days of peeing around with that motor for THIS!! :-(


RANGER


"KEEP YOUR LINES WET, YOUR POWDER DRY and THE BEER COLD"!

[EAGLE EYES]

Whoops, I forgot to add that you might have bad coil also. Just as you described your motor running, is how they act when they go bad. Either way I feel its spark delivery.

[Box]

I have a 82 50 hp, and if it is similar to mine, a likely source is that the screw cap on the gas tank is screwed CLOSED. The mercs that use the 6 gallon tank need that to be OPEN. At least on my year model.

I was at a cabin and the neighbor was having the exact same problem, and was looking for advice on carb kits and gaskets and mechanics. I told him - check the vent on tank. And that was it.

I hope that your problem is as easy! :)

Good luck,
Box

[REW]

1. Have an assistent at the back of the boat, when you take your boat out to test for this problem.

2. If you encounter the problem, have the assistent pump the squeeze bulb - until hard - while the engine is running to see if the performance improves.

3. If the performance comes back to normal - and if continued squeezing of the bulb - keeps the engine runninng properly, you have one of 3 proablems.
a. Defective check valve in the squeeze bulb, or other small leak or connection in the line, connection, and or bulb.
b. Partially plugged fuel filter - that is limiting the amount of fuel deliver, that is overcome by additional pumping pressure.
c. A partially defective fuel pump - that is assisted by the pressure from the externally pumped fuel bulb.

Solution:
If the fuel lines and or squeeze bulb are more than two years old, simply purchase a new line and bulb before going out and testing the boat and motor. If you encounter the problem, put the new line and bulb in place and retest. If the problem continues, then the problem is either b or c.

If the squeezing the bulb doesn't help the problem, then I would look at ignition as causing the problem with your engine. First install new plugs, if that doesn't cure it - and if you can say that you have an ignition problem - you are looking at a coil pack or power pack - depending on the particular model engine.

Take care

REW

[Gumby]

Thanks to all of you for your replies. I now have some very good ideas on how to find the problem; fixing it may be another story, but I have some very good friends and neighbors who may lend a hand. Thanks again to all of you, and thank God for this web site. It truly is the best.