Rebuilding 1985 mercury carburetors

SevenBoater

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Oct 5, 2020
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Hi, hoping for a little advice regarding my carburetor rebuilds. I am rebuilding the carburetors on my 1985 Mercury 50 hp two-stroke using QuickSilver kits part number 1395-9023. The top carb is stamped WMA3.1. The rebuilds have gone well so far with one exception. The kits have one less gasket than what was present in the carburetors. Specifically there was a very thin gasket between the pump diaphragm and the fuel pump body. I have attached a photograph with an arrow pointing at the extra gasket. My Clymer manual does not show this extra gasket. So.... should I re-use the old gaskets or should I install just the gaskets and diaphragms that came in the kits?
Thanks in advance for your help.

Unfortunately, when I try to upload the picture I get an error message.
 
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racerone

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Dec 28, 2013
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The thin diaphragm with the valve flappers is sometimes used to seal better.----With the brown gasket backing it up.----Your choice.-----Why did the carburetors need to be " rebuilt " here ?----What is the motor doing / not doing ?
 

SevenBoater

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The thin diaphragm with the valve flappers is sometimes used to seal better.----With the brown gasket backing it up.----Your choice.-----Why did the carburetors need to be " rebuilt " here ?----What is the motor doing / not doing ?
Hi racerone,
Thank you for your response. I decided to reassemble the carbs using only the gaskets and diaphragms that came with the kit. I then pressure tested them by hooking them to the fuel tank and pumping the bulb. They didn't leak so I am planning to reinstall them on the engine this week.

Regarding why rebuild: The boat has been running poorly at speed. Cranked easily and idled smoothly and without problem. At anything over half throttle it ran poorly. Skipped and sputtered. Took it to the shop and they checked compression and ignition system, replaced plugs, replaced fuel lines. That seemed to help but only a little. After running it a bit the problem returned. So, carburetor rebuild seemed like the next step. When I got the carbs off the motor I turned them upside down to move the float and open the valve and tried to blow into the fuel inlet. On one carb I was not able to push any air without jiggling the carb. On the other carb I was initially unable to push any air until I blew very hard. When I disassembled the carbs I found that the inlet needle valve was partially made of plastic. Hard to tell, but it appears that the plastic may have partially degraded. The needle valves in the rebuild kits are all metal, with no plastic. I am hopeful that degraded plastic was the problem. Otherwise the carbs were clean and not clogged and in pretty good shape. I hope to get them back on the motor this week.
 

SevenBoater

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Oct 5, 2020
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Update on my aggravating engine troubles. I put the boat in the water to see if my carburetor rebuilds solved my problems. Motor cranks easily and runs well at low speed. Unfortunately the problem with high speed operation was not fixed. At any speed up to about half throttle it runs great. When I push the throttle past that point the motor sounds different but does not go any faster. I noted that there seems to be more exhaust smoke when I push it to full throttle. I have replaced or cleaned nearly every component of the fuel delivery system and I am convinced that adequate fuel is passing through the carburetors. I even ran it on some new fuel yesterday just to be sure that sour gas wasn't the cause of the problem and that didn't help. I would appreciate any suggestions.
 

SevenBoater

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ARRRGH! The last mechanic who worked on my boat was certain that ethanol in the gas had ruined the fuel hoses so he replaced all the hoses. He also replaced the spark plugs and checked compression. I assumed that he was correct about fuel delivery being the problem so when it still didn't run properly I decided to rebuild the carbs. Rebuilding the carbs didn't help. Since I assumed that he had correctly diagnosed the problem, I never checked any part of the ignition system. Yesterday I decided to check. I grounded each spark plug wire separately, turned the engine over. When I disconnected the lowest spark plug and grounded it to the engine it cranked but ran very badly and the spark looked weak to me. When I disconnected the next wire up and grounded it against the motor I saw good spark and the motor wouldn't crank. Then the BIG surprise; no spark on either of the top two wires and disconnecting them didn't change how the motor ran at all! So it appears that I have been running on two cylinders. I am guessing that the coils are bad and I plan to replace the coils and the spark plug wires.
 

racerone

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Dec 28, 2013
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Most folks pick the carburetor cleaning / rebuild as step #1 for motor fixin.------ Sometimes I say that trouble shooting is becoming a lost art.
 

SevenBoater

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Oct 5, 2020
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racerone,
Thanks for your reply. I feel like a complete doofus for not checking the spark to bein with! Would have saved a lot of trouble. Now I still have to fix the ignition problem and I probably will have to take at least one of the carbs back off because I think I set the float too low as it is not fully closing the inlet needle valve. I will post an update when I get everything figured out.
 
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