75 hp merc power problems


Old 07-03-04, 04:47 AM
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75 hp merc power problems

I have a 1986 merc. 75 hp and am having problems. The thing idles but when put in gear the motor bogs out with no acceleration. what do you think.
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Old 07-03-04, 09:00 AM
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Hello: judu

A few common posibilities come to mind.

Ignition timing and or carb problems.

Other possible problems could be stale fuel, flow flow restictions anywhere in the fuel system to the carb, etc.

Would need much more specific and detailed information posted in a reply. Use the reply button to add more info.

Reading this post and several like it will help to diagnose common engine problems like the one you are describing.


The resident boat service & repair professionals may have additional helpful information, suggestions and advice. Check back on your question several times for additional replies.

Kindly use the reply button to add any additional information or questions, etc. to this thread. Using this method also moves the topic back up to the top of the daily list automatically.

Regards, Good Luck & Safe Boating.
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Old 07-04-04, 08:21 AM
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So far I have found water in fuel so I drained and replaced with new. I found the fuel pump diaphram was suspect, replaced that.
I have also tried to check the stator and trigger, my meter was'nt working properly. Also checked compression (140#-145# each cylinder). Have'nt checked timing yet.

What do you think?
Old 07-04-04, 01:14 PM
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Hi: judu

You're doing well thus far and may be on the right track.

Water in fuel system?
Did you flash out the tank and fuel lines?
Replaced the fuel filter?

If not, must be done completly to ensure the left overs and left ins are not recirculated back into the carb, pump, etc.

Replaced furl pump diaphram? Good. Does that mean the entire pump and assembly or just the diaphram? Hope it means the entire assembly and all the fuel passages, etc.

How about the carb? Prior stale fuel will plug up the carb and all it's internal fuel passages, etc. Any fuel restriction will drastically effect the engines normal operation as you originally described in the first post you made.

Once all the above are completed, mostly mechanical work, engine electrical and timing issues can be addressed. Which, in my opinion, should be the steps taken after the fuel system and carb are positively not the causes.

What do I think? Electrical system of the ignition and timing should be the last items to check. Not as likely, in my opinion, to be a direct cause of the problem you described. Carb and fuel problems must be checked first.

Alternate voltage output should be 14.5 volts or there abouts, at idle, which you mentioned the engine can run at. Thus a reading can be taken. If the boat already has a charge meter or gauge, it will show the output rate.
Old 07-04-04, 09:14 PM
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If you took a look at the thread that was added you will see I had the same problem.I did do some other things you might want to try.Initially when I started to try things to fix my boat I replaced the spark plugs.It did not change my problem but when we were out on the water after adjusting the idle we took out the plugs and they were really black.I was told that it was a good sign of running rich.An ajustment was made on the carb to lean it out.I didn't actually do it myself,but I was right there and it didn't seem to difficult.Origionally I had said that the boat idled fine in neutral,but seeing and hearing how it runs now I would have to say I was way off.What I should have been saying was "This boat idles like it wants to stall and when I put it in gear it does stall unless I am out of the water"Does this sound familiar?

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