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1974 7.5hp Carburetor Rebuild

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William01

Advanced Contributor
I’ve just rebuilt the carburetor based on the service manual. I was missing a few pieces as per the service manual so all the pieces are now installed. The engine is at the lake and the carburetor is at our winter home so I can’t field test my work until spring. I’m not the first person to have this carburetor apart!

1) Is there any bench testing that I can do to check my work?

2) Previous owner/owners had a pipe clamp around the fuel line between the Inlet strainer and the fuel supply inlet, presumably to mitigate a kink in the fuel line. No fuel pump on this engine so I’m wondering if I can lengthen the fuel line so there’s no chance of a kink forming?

3) What size fuel line? The manual or the parts list doesn’t specify what diameter fuel line is factory specification. It appears I currently have a 5/16” fuel line, measured with a drill bit. There is some resistance when sliding the fuel line on to the strainer nipple but the fuel line slides on fairly easily.

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racerone said:
??----The fuel pump is part of the carburetor.----Has a diaphragm operated by crankcase PRESSURE.
Click to expand...

Yes, you are correct. Service manual shows 2 gaskets and 2 diaphragms, my carburetor only had 1 gasket and 2 diaphragms. Mercury rebuild kit came with 2 gaskets and 3 diaphragms. The extra diaphragm was a light brown fibrous one that I understand is for ethanol blended fuel which I did not use since I only use non ethanol fuel. The missing gasket was the one between the fuel pump body and the strainer. The motor ran before my intervention but not very well. When I disconnected the fuel line the engine started to run like it should, don’t know if the missing gasket was causing my issues or over fuelling. The float was within 1/16” of the 1/4” float level the service manual calls for.
 
Thanks for the confirmation. That’s exactly how I put it back together, I used the rubber check valve instead of the fibrous one, can always change them out if needed. Note 7 is interesting, says to blow thru the outlet hole which I don’t have so I blew into the fuel intake with the carb right side up and after a brief second I could blow thru. I flipped the carb upside down and I couldn’t blow air thru so that tells me the float is working? Not much air pressure but in theory it’s a test.
 
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