1980 Mercury 40 wouldn't run much above idle

[YN2(SS)]

The other night, we took the boat to the lake and my buddy, who admittedly is "getting his feet wet" with his new boat tried to get it started, (might have flooded it), had a hard time, finally did and got it to the dock.
So I parked the car, got in the boat and we left the dock. With the throttle all the way forward, it ran just a little rough but it was if the throttle was moved only 1/4 way forward.
So we returned to the dock. The Commander control has a throttle only button that allows limited movement of the throttle cable without putting the motor in gear. This is like what we were experiencing and I thought maybe it was working like that when we were also putting it in gear. Checked it out, that wasn't what was happening. Removed and cleaned both plugs in case one was fouled and reinstalled them. Fuel line pressure was good. The motor had never done this before but it had been "tilted" all the way up for transportation for a week.
It was late at night so we floated next to the dock and had a "pop". When we were done, as a last ditch effort, turned the key and it started and ran normal with no other problems.

What happened? This almost ruined our fishing trip.

 

[YN2(SS)]

Re: 1980 Mercury 40 wouldn't run much above idle


OK,
So my buddy and I took the boat out on the lake again today and the same thing happened, except this time we kept the motor running and started putting out to the fishin hole and in about 25 minutes it "cleared it's throat" and ran pretty good after that. Any thoughts?

 

[YN2(SS)]

Re: 1980 Mercury 40 wouldn't run much above idle

Does this sound like a carb issue (stuck float maybe) or a problem with the ignition system (needs to warm up/dry out)?

 

[YN2(SS)]

Re: 1980 Mercury 40 wouldn't run much above idle

Another trip, same problem. Motor runs with reduced power for a period of time 20-30 minutes, clears it's throat, spurts, then takes off like a champ. Each time we shut it down on the lake though, it is a little hard to start. Sometimes if we pressurize the fuel line with the bulb, that gets her goin. Any thoughts?

 

[Fuzzytbay]

Re: 1980 Mercury 40 wouldn't run much above idle

Could be a few issues you have. My first question is on the spark plugs? Have you tried new ones. What did the ones you took out, look like?
In regards to more information needed. Has the motor been serviced lately?
The fuel, you mentioned the ball. Does it get hard, and stay hard when first starting? When its running, does it sound like its missing, or not getting enough fuel to "take off"?

 

[YN2(SS)]

Re: 1980 Mercury 40 wouldn't run much above idle

OK, so on the lake yesterday it did exactly the same thing. Low power pulling away from the dock. We just pointed it towards the middle of the lake and after 12 minutes with the throttle all the way fwd, it suddenly snorted/spit/surged/healed itself and took off. Ran like a champ the rest of the day. It is predictable.
I have done a lot of work on this boat and motor since spring to bring this boat and motor to life (too much to list) and it was running well. The first time this happened, (see first post), I pulled the plugs and cleaned them with starter fluid. Found a loose ground wire on the motor. Fixed that. Pressurized the bulb again. None of this healed the problem. Waited another 20 minutes while we floated (after the "pop"). Problem gone. I have not replaced any electrical/ignition components other than a rectfier all summer. Repaired some burnt wires coming out of the switch box assembly before we even started using it in the spring. Same plugs all along. The fuel line (tank to engine), fuel hoses on motor, fuel filter and housing are new. The whole fuel system was drained and dried and has no water or contaminants in it (verified). Fuel pump and carb rebuilt and idle set by me. I am a good mechanic, but not an experienced outboard tech. We have not yet taken it to a shop and had the carb adjusted by them or a link and sync done. The fuel bulb (new) pressurizes well, but one time recently, after the motor began running well, and we turned it off for bout 30 min, the motor would not start until I pressurized the line with the bulb, then she ran great.
I dont know if this is a miss. It doesn't run smooth or have much RPM when the problem is present. Or is this a lack of fuel? My gut is beginning to tell me this is an ignition problem that goes away when it warms up. There is usually 1 or 2 weeks between trips. So far, it has cleared up everytime and doesn't come back that day.

 

[Fuzzytbay]

Re: 1980 Mercury 40 wouldn't run much above idle

OK, so on the lake yesterday it did exactly the same thing. Low power pulling away from the dock. We just pointed it towards the middle of the lake and after 12 minutes with the throttle all the way fwd, it suddenly snorted/spit/surged/healed itself and took off. Ran like a champ the rest of the day. It is predictable.
I have done a lot of work on this boat and motor since spring to bring this boat and motor to life (too much to list) and it was running well. The first time this happened, (see first post), I pulled the plugs and cleaned them with starter fluid. Found a loose ground wire on the motor. Fixed that. Pressurized the bulb again. None of this healed the problem. .

I'd change the plugs. That way you know for sure you have no spark issue with them.

I have not replaced any electrical/ignition components other than a rectfier all summer. Repaired some burnt wires coming out of the switch box assembly before we even started using it in the spring. Same plugs all along. The fuel line (tank to engine), fuel hoses on motor, fuel filter and housing are new. The whole fuel system was drained and dried and has no water or contaminants in it (verified). Fuel pump and carb rebuilt and idle set by me..

OK when this type of work is done, you need to do a link and sync.

Still hard to nail down this problem, it could be ignition, or the fuel pump might be faulty. What did you do on the rebuild?

 

[guitchess]

Re: 1980 Mercury 40 wouldn't run much above idle

I have been research this type of issue for a week now and and most of the answers seem to be pointing toward ignition problems, specifically the switch box. This weekend I am going to do some diagnostic tests that will confirm/rule out this idea. My problems started exactly as yours. Eventually, you will not be able to achieve full power at all.

 

[YN2(SS)]

Re: 1980 Mercury 40 wouldn't run much above idle

Fuzzytbay,
I really appreciate your input. I'm gonna nose around inside the cowl, see if I see any thing obvious. We are going to pull the motor to do some transom work and then hope to put it back on and get it to the shop. I knew I had reached the limits of my experience on the "tune up" once the carb idle was adjusted. Following the SELOC manual I could not determine how to do a "link and sync" but would be able to once I saw it done or had more specific instructions. I probably need to find good instructions on how to test the stator and switch box. I have limited experience with my multimeter other than basic continuity, resistance and voltage measurements and it may not (probably isn't) a DVA? meter, which I guess I need for this and then I would still have to do the tests. So if this thread goes dead for a while, that's because of a transom rebuild and winter.

While I wouldn't wish trouble on anyone, I am glad to see someone else on here that is experiencing the same problem. Let me know what u find.

 

[YN2(SS)]

Re: 1980 Mercury 40 wouldn't run much above idle

P.S.

On the rebuild, I didn't touch the motor. I checked compressions early on and they were good. There might be compression problems on a cold motor now, havent checked that. The fuel pump was rebuilt.

 

[Fuzzytbay]

Re: 1980 Mercury 40 wouldn't run much above idle

Here is the link to the link n sync. Sorry I had thought i posted it earlier.
http://forums.iboats.com/showthread.php?t=168855
If you do a search for testing switch box's, here on Iboats I know the test is shown in several post's, (Thanks to Laddies for that).I have magneto driven motors, so I am cluless on the test's for switch box's and triggers.

 

[Nedly]

Re: 1980 Mercury 40 wouldn't run much above idle

Hi Guys I have recently aquired a tidy old 15 ft f/glass half cab fitted with a 1979 merc 50hp 4 cyl and it does exactly the same thing. It starts easily but for the first 20 min or so it will not rev then all of a sudden it takes off and runs like a swiss watch for the remainder of the trip. I have replaced the plugs and fuel line and I suspect the problem is electrical. Did you guys get to the bottom of this issue? And if so what is the hiddeous beast ruining our precious liesure time?
Sincerely hope you can help
Ned