1981 7.5 mercury with tillotson carb fuel leak problem

camoski

Cadet
Joined
Apr 9, 2013
Messages
6
Just bought a duck boat for me and my sons. The motor (1981, 7.5 mercury, tillotson carb) has sat for 8 years. I got her running and had fuel dumping out the front of the carb while it was running. I replaced the needle, float, gaskets and got everything running fine. Tested on the water and after running great for about 10 minutes it flooded out again and had fuel dumping out the front of carb. Couldn't get restarted, and forgot paddles, so dog paddled back to shore. Took carb apart and readjusted the float. I also noticed the diagram for the carb shows a spring that goes with the needle. There was no spring in the needle/float assembly when I first disassembled the carb. The new needle I received did not have a spring, but I just looked at another supplier and their needle comes with a small spring. Does anyone know if this needle should have a spring? I assume it goes between the needle and the float tab. Would the spring, or lack of the spring, cause the flooding issue? Could this be a problem with the reeds? I got it back together and running without the spring but I still have a small leak out the front of the carb. Appreciate any help....
 

Bosunsmate

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Apr 7, 2012
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6,129
Re: 1981 7.5 mercury with tillotson carb fuel leak problem

I would have a go and order the needle and spring.
I havent done one for a while but i think the spring is under the needle which helps keep the pressure up on the seat
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1981 7.5 mercury with tillotson carb fuel leak problem

I would check your year on your motor as Mercury had gone exclusively with the MerCarb on the 7.5s by the 1980s. If it has a Tillotson, it's likely quite a bit older...
 

camoski

Cadet
Joined
Apr 9, 2013
Messages
6
Re: 1981 7.5 mercury with tillotson carb fuel leak problem

I would have a go and order the needle and spring.
I havent done one for a while but i think the spring is under the needle which helps keep the pressure up on the seat

sounds good. I ordered the needle and spring and will see if it makes sense as far as fit goes when it arrives. Thanks!
 

camoski

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Apr 9, 2013
Messages
6
Re: 1981 7.5 mercury with tillotson carb fuel leak problem

I would check your year on your motor as Mercury had gone exclusively with the MerCarb on the 7.5s by the 1980s. If it has a Tillotson, it's likely quite a bit older...

OK, will double check the serial number when I get home. From what I recall the first two numbers were 56, which translated to 1980/81 on the chart I refersnced. Thanks for the help!
 

camoski

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Apr 9, 2013
Messages
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Re: 1981 7.5 mercury with tillotson carb fuel leak problem

OK, will double check the serial number when I get home. From what I recall the first two numbers were 56, which translated to 1980/81 on the chart I refersnced. Thanks for the help!

UPDATE: New needle w/spring attached arrived yesterday. Installed last night and motor started right up and ran great with no leaks or flooding. Will test on the water this weekend. Also reverified serial number and it comes back as a 1980/81: maybe someone before me changed the carb to a Tillotson?
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1981 7.5 mercury with tillotson carb fuel leak problem

Curious... Did they add a fuel pump? The MerCarb had the fuel pump built in, while a Tillotson would require a separate fuel pump.
 

camoski

Cadet
Joined
Apr 9, 2013
Messages
6
Re: 1981 7.5 mercury with tillotson carb fuel leak problem

Curious... Did they add a fuel pump? The MerCarb had the fuel pump built in, while a Tillotson would require a separate fuel pump.

The Tillotson on my engine has the built-in, diaphram style pump on the left side. I replaced all the the components and it seems to work fine.
 
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