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1987 Merc 25HP starting and running issues

R

rmcderm313

Regular Contributor
So the saga continues on my 1987 Mercury 25HP serial number 0B236965. I cleaned the carb and put everything back together. The engine won’t start in neutral. It starts every time if I put it in gear, with or without the prop engaged. If I let it run in gear it will stay running. If I let it run for a little bit and then drop it into neutral, it will run for about 60 seconds and then slowly die.

Even when I have it in gear it will start to bog down if I leave it at one “speed” for a minute or so. When that happens if I advance the throttle some more to keep it running, it will cough a bunch of white smoke and then eventually clear and stop smoking.

I’ve played with the idle screw, and although it does change how fast the engine runs, it doesn’t keep it running. I’ve ordered the carb rebuild kit, so that is my next step. I’ll replace all the gaskets, springs, needle etc. and see if that helps the issue.

Occasionally when trying to start it, each time I pull the starter rope, gas flows from the front opening of the carb (stuck needle?). This doesn’t keep it from starting in gear, and it doesn’t happen all the time.

The other thing that is happening is that the lower cowl is filling with water when the engine is running. I can’t really see where the water is coming from, but I’m thinking it is the adapter plate gasket. Part #6 in this diagram..

[url]http://www.boats.net/parts/search/MercuryMarine/0B236965/274/150/DRIVE%20SHAFT%20HOUSING%20ASSEMBLY/parts.html[/URL]

I have removed the engine block to have a look and it was in rough shape. I’ve ordered both that gasket and the driver shaft housing gasket (part #13), and I will replace both. Hopefully that will stop the water issue. I am getting a strong cooling flow so I don’t think it is affecting the way the engine is running, but I’m not sure.

Any opinions on whether the behavior I am seeing could be remedied by replacing the carb parts and fixing the water issue? What else could I try? I’ve got the engine block detached from the adapter plate so its a good time to look at other stuff while it’s off.

Thanks,
Rob

 
It starts every time if I put it in gear, with or without the prop engaged.
Click to expand...
Huh? Stop messing w/the idle speed and get the carb thoroughly cleaned. Idle speed is adjusted under a load in the water. Are the plugs burning medium brown?
 
I did clean the carb really well, but I haven't replaced the gaskets and springs etc. I just got those today.

Was your exclamation of "huh?" regarding the fact that it's starting with the prop engaged? I know. I think that is related to the fact that this was set up as a remote start/shift, but I have disconnected the starter control cable, but I still have the remote throttle linkage connected. I need to remedy that before taking this on the water. Obviously don't want to be able to start in gear with the prop engaged. I hope I will be able to fix it so it can only be started while the remote shift is in neutral. For right now I'm just trying to get it running close to correctly.

I can't tell much about the plugs. They are those NGK BUHW plugs without the gap so I can't see much of any color on them. They look pretty clean actually.

I'm hoping the gaskets and such help the issue. If not, I'm not sure where to turn next.

Thanks for the reply,
Rob
 
Here are the plugs:

photo (5).jpg
 
Keep in mind I'm using the pull start rope, it cranks but won't fire. It even starts to chug a little bit sometimes, but never starts. I'm 99% sure I was checking for spark with it in neutral and I was getting spark. I have a harbor freight spark tester that just lights up so I can't tell how strong the spark is.

I'm thinking that it's some kind of fuel delivery issue when in neutral. I need to go through the service manual and check all the starting points for the carb. Float adjustment etc. Is there some starting point for screwing in the main jet at the bottom of the bowl or do you just screw it in?

Thanks for the reply,
Rob
 
Is there some starting point for screwing in the main jet at the bottom of the bowl...
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Turn it inward until it barely tightens and back it out 1 & 1/2 turns to start. To check spark use any lawn mower spark plug w/an electrode and adjust it to .030", attach it to a plug wire and hold it on the head to ground the case...pull start it to see the spark. Orange or white spark is weak.
 
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