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Merc 650 help

BingerFang

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Hey guys, recently picked this 1968 Mercury 650 4cyl for my pontoon boat. It ran great at the guys house, fired up every time. Took it out to the river and ran it for a while and it ran great. Shut it off and it would not fire. It took me 10 minutes of fiddling to finally get it to start and idle. It now has this weird cough when I finally get it to idle.. I'm thinking I may have gotten bad 87 at the pump or maybe the fuel filter is clogged and that could be the reason why it's so hard to start? I have a video of the cough here:

I have 0 knowledge on outboards, was hoping someone could help.

Thanks
 

Ragged Edge

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Looks and sounds like a lean sneeze. Replace the fuel filter to start, does the boat have a water separator filter in the fuel line? Every boat should run one but I know not everyone does. Next would be carb cleaning as they could be gummed up or have some debris in them restricting fuel flow, could also be bad reeds and I have seen poor timing cause a condition similar to this as well. If you want a mechanic to check it out take it to Al's Outboard in Havasu. 928-453-0256

Oh, if this was my motor I would be running 91 octane at a minimum of 40:1. Good synthetic 2 stroke oils smoke less, (Klotz, Motul, Torco) but the Merc stuff is good as well.
 

BingerFang

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Looks and sounds like a lean sneeze. Replace the fuel filter to start, does the boat have a water separator filter in the fuel line? Every boat should run one but I know not everyone does. Next would be carb cleaning as they could be gummed up or have some debris in them restricting fuel flow, could also be bad reeds and I have seen poor timing cause a condition similar to this as well. If you want a mechanic to check it out take it to Al's Outboard in Havasu. 928-453-0256

Oh, if this was my motor I would be running 91 octane at a minimum of 40:1. Good synthetic 2 stroke oils smoke less, (Klotz, Motul, Torco) but the Merc stuff is good as well.

Ragged, thanks for the reply. I will richen up the air/fuel mixture tonight and give it a try. Do you have to take the carb off to replace the fuel filter? Also, it does not have a water separator in the fuel line, I will be sure to add one. I've cleaned many dirtbike carbs over the years but taking apart this outboard to service the carbs seems intimidating, I don't even know where to start unbolting things to get to it and really can't find anything online.

I was told to run 87 only in these motors but will dump my fuel out and try 91. I only use Motul 2t for my 2-strokes at 50:1 and tried the same on this motor. I will wrench on it tonight and maybe take it to AL this weekend if I can't get it figured out.
 

Ragged Edge

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The fuel filter on these older motors (if it has one) will be inline much like you would see on older carbureted dirt bikes. I have seen outboard boats with no fuel filter at all and some with just a fuel screen in the fuel pump. That's another thing to look at as the fuel pumps (probably have two) on this motor would have a rubber diaphragm that could have small tears in it so not working at full capacity. Another problem with these old motors is the fuel lines can break down on the inside putting small bits of rubber in your fuel pumps and carbs, so check your fuel lines.

The carbs look more complicated than they are, just make sure to turn the idle screw all the way in first and count the turns so you know where to put it on reassembly. Probably be about 1 & 1/2 turns out. This link has a diagram of the 3 cylinder 650 fuel pump, fuel lines and filter set up :https://www.marineengine.com/parts/...-fuel-filter-and-fuel-line-serial-group-no-11 , 18 thru 26 would be the fuel filter.

Here is a 650 carb schematic, should be similar to what is on your motor.
 

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Ragged Edge

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Unbolt and remove the upper cowling to gain easier access to the carbs.
 

BingerFang

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Unbolt and remove the upper cowling to gain easier access to the carbs.

Thanks for all the supplied information, I greatly appreciate it and will take a look when I get home.

The carbs are behind the distributor on one side and the starter on the other.. seems almost impossible to reach to work on without taking a ton of things off. Any ideas on how to go about this?
 

white tortilla

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Thanks for all the supplied information, I greatly appreciate it and will take a look when I get home.

The carbs are behind the distributor on one side and the starter on the other.. seems almost impossible to reach to work on without taking a ton of things off. Any ideas on how to go about this?

If this is the case, I would suggest first removing the distributor and starter to make it easier to remove carbs. Best thing is to take pictures as you go so its easy to reference when putting back together. Also check flogger bar on the outside of the carb where the choke attaches they tend to get out of adjustment on these old mercs which can contribute to the popping your hearing.

[emoji1360]
 

BingerFang

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If this is the case, I would suggest first removing the distributor and starter to make it easier to remove carbs. Best thing is to take pictures as you go so its easy to reference when putting back together. Also check flogger bar on the outside of the carb where the choke attaches they tend to get out of adjustment on these old mercs which can contribute to the popping your hearing.

[emoji1360]

Lol, I'll just wait until this weekend and I'll let you do it.
 

BingerFang

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Sooo..... got home yesterday and let her warm up. She was still sneezing like usual. Counted the air/fuel screws and the top one was 1/2 turn out and the bottom was 1 turn out. Set them both to 1.5 turns out and she purrs like a kitten now. Thank you very much for all your help Ragged!
 

Ragged Edge

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No worries, happy to help. Good to hear that it looks like a simple adjustment resolved the issue and you don't have to start taking it apart.
 

HST4ME

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Sooo..... got home yesterday and let her warm up. She was still sneezing like usual. Counted the air/fuel screws and the top one was 1/2 turn out and the bottom was 1 turn out. Set them both to 1.5 turns out and she purrs like a kitten now. Thank you very much for all your help Ragged!

Those were great running motors, but I will say this you have a hobby now. ;)
 

BingerFang

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No worries, happy to help. Good to hear that it looks like a simple adjustment resolved the issue and you don't have to start taking it apart.

Ran it all last weekend and she ran like a peach! Roasted my brand new prop Friday... Wasn't even mad I had to buy another new one since the boat was running so good.

Will post a photo for laughs below!

IMG_9444.jpg
 
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