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Won’t stay running

C

ChuckL

New member
I am working on. A 1956 Evinrude 7.5 and am experiencing starting issues I believe are fuel related. The motor starts and runs on fuel accumulated while choke-starting but won’t stay running longer than a couple of seconds. The primer on the tank builds up pressure and pumps fuel to the carb fine. After the fuel hose coupling, the air hose connects to a nipple in the intake manifold on the block, behind the carburetor . It reads vacuum, not positive pressure! Shouldn’t that line supply positive pressure to the tank?
 
That line provides positive pressure to the tank.-----Perhaps there is an issue with the rubber flappers / check valves inside the manifold.
 
????---No-----Reed valves are metal.---Reed valves are for crankcase induction.------The rubber check valves are used to pressurize the fuel tank.
 
Reed valves allow air to enter the crankcase.-----The rubber flapper check valves open as needed to allow air OUT of the crankcase.----The rubber check valves open a lot on start-up.----Then only a little bit to maintain pressure in the tank as fuel leaves the tank.
 
racerone said:
Reed valves allow air to enter the crankcase.-----The rubber flapper check valves open as needed to allow air OUT of the crankcase.----The rubber check valves open a lot on start-up.----Then only a little bit to maintain pressure in the tank as fuel leaves the tank.
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That sounds like the right direction. I’m not familiar with them, but it sounds like they might relieve back pressure like a compression relieve valve, which would be appreciated. Can you tell me where they are located on the engine so I can refer to the parts diagrams for ordering? Perhaps also the part number? Thank you so much for your assistance and support.
 
Note---- the primer on the tank does NOT put air pressure on the tank.-----The primer only pumps fuel into the carburetor.-----No rubber flappers don't relieve back pressure.-----Easy to find on the parts diagram.------On the reed valve plate.
 
Thank you for all that info. I haven’t worked on this vintage outboard since my teens and even then, my experience was limited.. and I’m 70 now. Sharing your experience and advice is greatly appreciated. I’m going to go into the reed valves and check it out. Do you know where those flapper valves are available?
 
I’m back, and hopefully not like a bad penny. I removed the reed valve plate and removed the flapper valve. It is retained by little metal arms with tiny screws with even tinier spacers establishing a set height tolerance for those arms. I inspected the rubber and found no signs of wear or failure and the plate on which that ruber flapper seals was smooth and clean, but noticed the little metal arms laid right against the rubber leaving no space to “flap.” Wondering if this is correct, or if there is a specified tolerance for movement that could be adjusted with a gap? Also, took note of the two passageways supplying the air pressure to the flappers. There didn’t seem to be anything blocking the openings but wondered if you can suggest how to check for a clear passage through those ports?
 
racerone said:
order them from this very website if you find they are bad.-----click on boat engine parts.
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I’m back, and hopefully not like a bad penny. I removed the reed valve plate and removed the flapper valve. It is retained by little metal arms with tiny screws with even tinier spacers establishing a set height tolerance for those arms. I inspected the rubber and found no signs of wear or failure and the plate on which that ruber flapper seals was smooth and clean, but noticed the little metal arms laid right against the rubber leaving no space to “flap.” Wondering if this is correct, or if there is a specified tolerance for movement that could be adjusted with a gap? Also, took note of the two passageways supplying the air pressure to the flappers. There didn’t seem to be anything blocking the openings but wondered if you can suggest how to check for a clear passage through those ports?
 
OK. With your help and advice, I have discovered two problems with my motor. In trying to cure the stalling problem, I discovered my tank was not getting pressurized. I started by checking for air pressure at the hose barb on the reed valve plate using a pressure gauge. As the gauge works to measure both pressure and vacuum, initially, I read the gauge wrong and thought it was showing vacuum. The actual problem was that the fuel hose connector was leaking the air even after I replaced the O-rings inside. It appears now that the hose connector is worn and has too much slop after connected. I have proven this by disconnecting both ends of the air supply hose at the connector and used a piece of 3/16 brake line tubing to bypass the connector and now I have air pressure to the tank and a steady fuel supply to the motor. During this troubleshooting period, I installed an inline fuel filter just before the carb that allowed a visual inspection for fuel. Seeing fuel, I had suspected the carburetor float valve to be failing, so I ordered a carb rebuilding kit which included a new float and valve with the seat. BEWARE EVERYONE! The stalling problem became worse! After double-checking my carb rebuild, I took notice of the new float valve and observed a tiny rubber tip at the point. After trying the float valve by holding the carb upside-down, lifting the float and trying to blow into the carb fuel barb, it blocked as it should. But when holding the carb right side-up I could not get any air passage; the needle stuck into the valve seat because of that rubber tip. The original needle and seat was machined to equal tolerances and was of higher quality. The design using this rubber tip like an old drain plug is NOT a modern improvement, but a problematic repair. Having damaged the original float valve seat due to almost 70 years in place, I am now looking for a NOS replacement.
 
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