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65 hp Mercury outboard bogs under load

D

drivewayguy

New member
I just purchased a boat with what i believe a 1975 mercury outboard.

The motor starts and revs up nice in neautral, when you engage it and try to punch it just goes oh about 8 MPH.

I chaneged the plugs really really good spark,

Compression in Top Cylinder is 135 psi the bottom two are at 130 psi so that is good

So i have good spark good compression and i have fuel delivery at least for good idle, i tried running some carb cleaner through and it mad a differenc in the idle stage immididate response when you give it gas but still no go when i put it under load.

I am thinking maybe dirty carbs but they look really clean however i am no mechanic just picked up a lot of stuff over the years.

Any ideas as to what i could look for now, or any links to show how to clean the carbs on those motor`sÉ

All help would be greatly appreciated.

Thanks Don
 
If those are the cvarbs that bolt to the block with long bolts from the front, you need to remove the bowls and clean out the tiny passage in the bottom that feeds fuel to the idle circuit.

The video below reveals how badly the motor "takes gas" when just one of those carbs need cleaning. Note how it reacts towards the end of the video.


http://www.youtube.com/user/57Fastjeff?blend=20&ob=5

Jeff
 
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If nothing else, run some seafoam through the engine with some fresh gas. You really shoudl consider pulling the carbs and cleaning them. how big of a boat are you pushing? And how much are you willing to try yourself? Fuel pump diaphram might have holes. Fuel filter might be dirty.
 
I wonder, does gas really go bad because i topped of the fuel that was in there already it took only ten litres to fill it. Could this cause my issue.

I am going to put all fresh gas in it today and try it out.

If it does not work then i am pretty confident in trying to take the carbs off and try to clean them if i can get some kind of instructions to take them off.

Would pictures of the motor be of any help?

Thanks for the replies

Don

Where is the fuel filter located?
 
.."Where is the fuel filter located? "

Follow the fuel line from the pump to a round thingee--that's it.

Jeff
 
i personally have experience of this. My boat ran well in the water but the second you tried to pull a wakeboarder it struggled. Carb cleaner and fuel stabilizer and new fuel = whole season of hassle free boating. If these guys say clean your carbs, they mean it.
 
I have had an interesting experience with a 65hp Merc I believe mine is a 1975.

Purchased it a couple of years ago as the fellow got mud in the engine....sucked it up into a cylinder. Anyway redid the engine. Fellow that helped me had a ton of experience with boat and small engines. He set the carbs and timing on it. Used it for the past couple of years but it always idled crappy and when starting it cold, man I cranked and cranked it. Seemed like once we got it going run fine.

Last weekend it worked the same on Friday night.... Saturday morning only running on 2 cylinders. I troubleshot it and found eventually that there was no spark on one cylinder. You can actually move the wires on it's cdi to tell whether it comes from a faulty coil, etc. It was the cdi. It would run but dies as soon as put in gear. If I held my mouth just right I could keep it from stalling and drive it 5mph or so with it.

I borrowed a cdi off of a buddy and tried it. It fired up immediately and actually ran about 4-500 rpm's faster. I had to go and adjust the idle down.

So looked on Ebay and found a brand new cdi out of Florida for $105....from Merc it was almost $400. Same box. It only takes about 5 minutes to switch the cdi.

Good luck.
 
Well the plot sickens.

Getting tired of working on this motor.

Last night boat was working great, day before working great. But then it did the same thing last night again and is only running on 2 cylinders. When hooking up the different CDI the other day, a small piece of the insulation on one of the wires fell off and I noticed that the wires inside were very corroded. Tonight I am going to rewire the CDI, etc with new wire. I have also noticed on other occasions that moving the wires around made it work better. Moved them around last night and couldn't make it better. I had thought that it may have been cross firing being that we really weren't careful how we placed those wires after doing the engine.

Perhaps they are just not making a good connection.
 
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