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7.5 Mercury Wont Start


jeremy28c's Avatar
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05-20-10, 11:51 AM   #1  
7.5 Mercury Wont Start

I have a 70's model Mercury 7.5hp outboard that I cant get started. If I spray a little starter fluid in the carb it will start up till its burnt it out and then nothing, Its getting plenty of fuel in the bowl so I put a new carb kit and fuel pump kit in it today and the same thing. Any thoughts would be great. Thanks

 
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samuari's Avatar
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05-20-10, 08:50 PM   #2  
There could be a couple issues causing this.
First thing I would look at is to be sure all the jets in the carb are clean as well as all the passages.

Also check compression, if it's low the motor will run on the starter fluid because it burns faster than gas.

Another thing with a 2 stroke of that age could be the seals on the crankshaft or crankcase are leaking the motor will not create enough vacuum to draw fuel into the crankcase.

 
jeremy28c's Avatar
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05-24-10, 04:45 PM   #3  
I think Im going to pull the carb again and see what happens. It has plenty of compression. Maybe it donts have enough vacumn to run the pump. Is there a way to check for that?

 
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05-24-10, 09:49 PM   #4  
It's hard to test vacuum without the motor running, but with the primer bulb you can fill the carb bowl and don't need the pump at start up. I would say it's more likely a problem with a jet in the carb.

Good luck.

 
tct64's Avatar
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08-08-12, 07:00 AM   #5  
First time on this site, so hope doing this right. I also have a 7.5 HP Mercury (1969) that I haven't started in years but would like to sell - trying to get started, but no spark. Was told to check points, but not sure how easy they are to get to - kind of afraid I might screw something up if I take off the top of the coil

 
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08-09-12, 04:22 AM   #6  
Welcome to the forums. I strongly suggest that you buy a Service Manual. It will take you step-by-step through any procedure.

https://webapps.brunswick.com/litreq/navigate.do

 
Northern Mike's Avatar
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08-09-12, 05:40 AM   #7  
Welcome to the forum.
Did you try changing the plug (I think there is only one in the 7.5hp, can't remember.)
It is a 2-stroke, so a new plug would be the first thing to look at and they are cheap anyway.

 
Samue's Avatar
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08-09-12, 06:03 AM   #8  
go to auto parts store and get a can of Sea Foam auto marine fleet Motor Treatment for gas and deisel engines. Add as directed to gas or gas oil mix . It cleans carburator jets , injectors . removes moisture from fuel , stabilizes fuel, frees lifters and rings, cleans carbon. It costs a little more than carburator cleaner. 7-8 bucks -16 ozs.. two-three ozs per gal of gas. + it works.

 
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