98 Merc 25HP issue

Gents,

This past sunday, I took the boat out, and it ran fine during our morning transit. Later in the day, I was running to another spot and when I placed the throttle handle into Neutral, I noticed that we were still making forward progress. I eventually had to hit the kill switch to stop.

I made sure the motor was in neutral, and when I started up, it sounded like I was running wide open (however, it was in neutral and the prop wasn't spinning) I quickly engaged the throttle so not to burn up the engine, and I ran it back to the launch until I got close enough and hit the kill switch again to stop and coast in. I realize that its not a good idea to engage the prop when running such high rpms. I haven't done it since.



I have spent the past few days working on it, but can't seem to find a problem. I actually don't even know where to begin to look. Most responses are that its a linkage issue. When I manipulate the throttle, all of the linkage on the side seems to operate correctly.


Any suggestions would be great. Thank you for your time.

Trey Knight
(904) 716-4604

Re: 98 Merc 25HP issue

Is this a 2/4 stroke? What is the engine s/n?

When you are manipulating the throttle can you verify that the butterfly in the carb throat is moving?

Gerry

Re: 98 Merc 25HP issue

It is a 2 stroke, S/N 0G683435

If by butterfly, you mean the little flapper part in the intake portion... yes it does move. its basically closed at Neutral, and horizontal when wide open.

Re: 98 Merc 25HP issue

S/N 0G683454 typo on the last post

Re: 98 Merc 25HP issue

Your s/n comes up as:

MERCURY - ( 25 H.P. (1998 ))
Serial No: 0G683454 Model No: 1025201UD

Parts Listing for model 1025201UD :

Mercury Parts, 20/25 H.P. 15/20/25 SEA PRO/MARATHON SUPER 15

Service Manual P/N: 90-826883R03

If you don't have the manual, send me a PM with an email address and I'll send you a copy.

If the butterfly is operating and the linkage appears to be ok I think I would have a look at the reeds to ensure there is no damage to any of the petals as it sounds like the fuel flow is not being controlled. Did this problem happen out of the blue? Was any work done to the carbs recently?

Gerry

Re: 98 Merc 25HP issue

Gerry,

Thank you for the help, I do have an electronic copy of the manual. I rebuilt the carb about three weeks ago, replacing all of the seals. I have used the motor three times since, and it ran fine. I am in no way ruling out that it could be a fuel issue, I just don't understand fully how all of it works.

I guess my thing would be as to why I couldnt' get the prop to shift into neutral until after I shut the motor off. Slowly but surely I will have torn this motor down and built it up enough to know everything about it.

Thanks for any advice you can give.

Re: 98 Merc 25HP issue

Also,

I believe its the shifting rod (the rod with the two holes that goes onto the ball joint area near the cables) anyhow, the plastic part that clips onto the ball joint is cracked, so it bends when I shift. I don't believe its enough to cause the issue, but I know I will need to replace it as well. I can tell that it will probably pop off when I use it if I don't replace it.

Re: 98 Merc 25HP issue

Sorry, I thought you said that you could not reduce the rpms to idle. I'll have to re-read your first post.

Gerry

Re: 98 Merc 25HP issue

I can't reduce the rpms to idle, you are correct. When I shift to what would generally be neutral, I still make forward progress at about 10 mph. once I kill the motor, and started back up, the prop was in neutral and it wasn't moving, but the rpms were still through the roof.

I do apologize if I'm causing confusion. This issue has me stumped.

Re: 98 Merc 25HP issue

Okay, once more, you say that when you shift back to neutral, you are still making about 10mph. The thing I am looking for is the effect of the shifter on the engine rpms. Therefore as you come back to neutral, are the rpms decreasing accordingly or are they remaining at full rpm?

Gerry

PS. No apologies required. When you have screwed up as many times as I have, then you can start to worry.

Re: 98 Merc 25HP issue

When I go from full throttle to neutral, the RPMs do decrease accordingly, and they sound correct for the speed I am still traveling. It's when I start back up, and the prop isn't spinning, the RPMs still sound as they did when I shut down, which is much higher than when normally at neutral

Re: 98 Merc 25HP issue

Maybe it is just me but I am having a difficult time understanding. In post #9, you say that when you started up, the rpms were through the roof.

In post #11, you say that when you started back up, the rpms are much higher in neutral than normal.

What type of setup do you have, remote control, tiller or side shift?

In posts # 6/7, you talk about not being able to shift into neutral until the engine is shut off and damage to the shifting rod. Can you identify the damaged rod end in the parts listing?

Gerry

Re: 98 Merc 25HP issue

Gerry,

I guess I can see your confusion as I change up the verbage with each post.

The broken peice is number 15 under the Throttle and shift linkage (Tiller shift)

- In regards to RPMs when starting up in neutral... they are extremely high.. I relate the RPM's to the sound of the motor..When I was on the water, and unaware of the problem, they were extremely high. Now that I know there is an issue, as soon as I start it up and I can tell that its not right, I instantly shut it off. I was told that I can burn the motor up if I let it run at high rpm's in neutral, so I don't leave it running long.

- In regards to shifting into neutral. When i was on the water, and the tiller was in the neutral position, I was still making way. I shut the motor off, and started back up (tiller handle still in the same position), and the prop didn't spin. So basically, once under way, when I shifted in neutral, it didn't take... However, as soon as I shut off and restarted, it was in neutral(prop not spinning), but the rpms were very high.


I hope this makes sense, because for some reason, I have a feeling that you will be able to give me some good trouble shooting tips. If this still confuses you, feel free to call me if you don't mind and I will be more than happy to talk you through it.

Thanks again,
Trey Knight
904 716-4604

Re: 98 Merc 25HP issue

Well seeing as item 15 is on the throttle link, I think it would be a good idea to get that replaced as the rod ends are plastic and depending on where it is cracked you probably don't have a solid dimension between the two attaching points. Therefore, if the rod end is opening up everytime you apply an action to it, you are not making a correct selection whether it is the throttle or the shift link. The rod ends are only a couple of dollars and I presume you have a dealer somewhere near you in Florida. I would examine the rod ends on the shift and throttle links and get them replaced before starting it up again.

Gerry

Re: 98 Merc 25HP issue

Thanks for the help. I will be replacing the part tomorrow then testing again