1984 Merc 7.5 won't throttle up in gear (RESOLVED)

Hi all - I discovered this site while searching for an answer to my recent, sudden problems with my outboard. I haven't been able to find a post that quite describes what's happening to my old merc.

The outboard is on the back of my 26' sailboat. I went out the other night in pretty fun conditions: big wind and big waves. The motor was fine on the way out. When it came time to motor back into harbor, I couldn't get any power in gear. Luckily the wind was blowing me "in", so we made it safely back to the slip. (the motor usually can push the boat about 5.5 knots - I can't even get it up to 2 now)

It seems fine in neutral. Even in gear at idle is acts as it always has. When I try to throttle up, it doesn't rev up; instead, it just shakes more and sounds pretty terrible.

My initial thought was that maybe while we were sailing in the waves, the motor got banged around and a plug wire came loose. Checked the plug wires, and no problem.

With all the vibrating and shaking I thought: "Maybe only one cylinder is firing, even though it seems ok in neutral...". I changed the plugs. The motors starts easier with clean plugs, but otherwise, no change.

A sailing friend said it sounded like I had weed wrapped around the prop. There's nothing visible, but there's certainly lots floating around that maybe have gotten twisted around it at some point. Is it possible that it's wound so tight I can't see it?

It's difficult to work on the motor as it's hanging over the water - it's a huge deal to haul the boat out. Anyway, I might be able to borrow a dinghy to get a closer look at it.

Any ideas what I should look for?

Re: 1984 Merc 7.5 won't throttle up in gear

Re: 1984 Merc 7.5 won't throttle up in gear

*bump*

No ideas?

Another friend has recommended something called "Seafoam"... that sounds a little too easy, but I'll try it.

Re: 1984 Merc 7.5 won't throttle up in gear

Re: 1984 Merc 7.5 won't throttle up in gear

"It seems fine in neutral. Even in gear at idle is acts as it always has. When I try to throttle up, it doesn't rev up; instead, it just shakes more and sounds pretty terrible."

This makes me think its a fuel / air thing ...


I'll take a shot at it, I guess ...


Check and see if in the "big wave" activity, that maybe your choke adjustment got knocked about in the big wave fun ? ...

fuel line connected as normal ?

Water got into your fuel source / fuel line somehow ?


It was pretty wet and windy, by your account ...

Re: 1984 Merc 7.5 won't throttle up in gear

Re: 1984 Merc 7.5 won't throttle up in gear

Thanks for the reply.

This motor has a manual choke, which still opens and closes the little round "door" on the front of what I presume is the carburetor just fine. I suppose it's possible that the door isn't closing tightly? I've never really looked at it before, but it seems ok to my eye.

The fuel line gets disconnected and reconnected to the portable gas tank each time I use the motor. The fuel line is still connecting as normal.

The tank was almost out of fuel last night, so I filled it with fresh stuff. No improvement.


I found another thread Re: suspected dropped cylinder that suggested removing a each plug wire in turn while the motor is running to determine if both cylinders are firing (i.e. if by removing one of them the motor stops, then you know that's the only cylinder that's working).

Re: 1984 Merc 7.5 won't throttle up in gear

Re: 1984 Merc 7.5 won't throttle up in gear

good deal ...


maybe it is an electrical issue if the motor or wiring somehow did get wet while you were out there ...

Re: 1984 Merc 7.5 won't throttle up in gear

Re: 1984 Merc 7.5 won't throttle up in gear

Just wanted to update this post with progress, in case somebody else experiences the same issue.

I think we found the problem.

After removing the prop (surprisingly easy to do) and confirming that it was not wound up in fishing line or seaweed, we tried the trick of removing a plug wire (the engine runs for a bit on one cylinder, and I got my fingers shocked a few times - it's not bad though)

Removing the carb everything looked clean but we noticed this little arm thingy that didn't seem to do anything. It seemed weird to have a plastic arm not attached to anything...

A bit of investigation led us to realize that it was supposed to open the throttle door on the back of the carb. The "throttle lever" is on the top of the carburetor (it's the little plastic arm) and it was not gripping the throttle "knob" tightly enough to actually open the throttle door. The plastic was a bit cracked. There's a little screw there to tighten, which we tried, but the plastic just broke. So I think if I find a replacement arm we should be good to go.

It seems that what was happening was that the spark was being advanced when I twisted the handle, but there was no extra fuel mixture getting into the engine, hence it only revs up slightly, then shakes all over the place as the sparks are sparking too fast for the the cylinders.

Anyway, I'll post an update in a couple days (hopefully) when the parts store opens after the long weekend to confirm that we got it right.

Re: 1984 Merc 7.5 won't throttle up in gear (RESOLVED)

Just wanted to confirm that indeed it was the throttle lever (Merc Part No. 44425) that was the problem. Once the new one was installed (a 5 minute job) the motor throttled up better than ever. It leads me to believe that this part had been on the verge of breaking ever since I got the boat a year and a half ago.

Anyway, it's all good now. $11 for a little plastic part is much easier to deal with than mechanic's hours

Re: 1984 Merc 7.5 won't throttle up in gear (RESOLVED)

Good going!