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20hp mercury stalls

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WoodyS

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I have a 1996 20hp mercury serial number 0G473300, that will stall unless I pump up the ball on the fuel line every minute or two. It has a new diaphragm in the fuel pump. The carburetor has been cleaned. I've checked for leaks in the fuel line and found none. I even took off the ends of the fuel line and connected the motor end directly to the carburetor nipple and stuck the tank end directly into the gas tank thinking there was a leak somewhere in the connections or in the fuel filter but nothing changed. Could there be something wrong with how the fuel pump gets its pressure and vacuum pulses? There is no external hose that connects to the carburetor, the carburetor gets its vacuum from a passage leading from the engine. I have been working on this problem for a while and can't figure it out. I'm sure someone has dealt with this before but it's got the best of me. Help please.
 
Yes there could be an issue with the PRESSURE pulses.----Reed valves or crankcase seals.-----You can start with a cylinder compression test.-----Post your numbers.----That may offer a clue to crankcase compression.
 
Welcome. Another question is when or how did the problem begin? Is that little pulse hole coming from motor to carb, open, plugged, or leaking? Did it indicate pulses when carb was off and you pulled it over?
 
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When was water pump impeller changes last ??----So many folks want to run and run these motors with no critical maintenance.---Almost every one of these motor should have had 3 new impellers in those 25 years.-----You risk damage to pistons etc , because often these motors do not have a warning or shutdown system for overheating !!!
 
I was going down the lake and it stalled. It cranked a couple of times and then I think it flooded and that was it for the day. I had the carb rebuilt and it would crank and run for a while and then stall unless I pumped the bulb every little while. That's when I started checking all the connections in the fuel system as I mentioned in my post. I did check the port in the engine and it wasn't plugged but I did not check to see if there was a pulse as the engine was cranked. I'll do that tomorrow. I've not done that before, what should I look for? Thanks for the input.
 
I changed the pump a couple of years ago but the motor hasn't been run much since. There is a good stream coming from the weep hole. Thanks
 
WoodyS said:
I was going down the lake and it stalled. It cranked a couple of times and then I think it flooded and that was it for the day. I had the carb rebuilt and it would crank and run for a while and then stall unless I pumped the bulb every little while. That's when I started checking all the connections in the fuel system as I mentioned in my post. I did check the port in the engine and it wasn't plugged but I did not check to see if there was a pulse as the engine was cranked. I'll do that tomorrow. I've not done that before, what should I look for? Thanks for the input.
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How did you check the pulse port with the carb on? Take the carb off and see if the base gasket is on correctly all holes must line up. Or did the use the wrong base gasket?
 
WoodyS said:
I was going down the lake and it stalled. It cranked a couple of times and then I think it flooded and that was it for the day. I had the carb rebuilt and it would crank and run for a while and then stall unless I pumped the bulb every little while. That's when I started checking all the connections in the fuel system as I mentioned in my post. I did check the port in the engine and it wasn't plugged but I did not check to see if there was a pulse as the engine was cranked. I'll do that tomorrow. I've not done that before, what should I look for? Thanks for the input.
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How did you check the pulse port with the carb on? Take the carb off and see if the base gasket is on correctly all holes must line up. Or did the use the wrong base gasket?
 
I did have the carb off and looked in the port. I used the gasket that came with the kit. I will check to make sure it doesn't cover the port but remember this issue started before I did anything to the carb.
 
Flying scott you get the grand prize! the hole in the base gasket did not line up with the hole in the crankcase. It lined up with the hole in the carb which I had seen before but I hadn't noticed the misalignment on the block. The compression was 120 on both cyclinders by the way. Gentlemen I thank you all for your input on this problem of mine.
 
WoodyS said:
Flying scott you get the grand prize! the hole in the base gasket did not line up with the hole in the crankcase. It lined up with the hole in the carb which I had seen before but I hadn't noticed the misalignment on the block. The compression was 120 on both cyclinders by the way. Gentlemen I thank you all for your input on this problem of mine.
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That is a pretty common thing with those.
 
He gets lucky once in awhile.
But seriously....you came to the right forum....got some top notch techs here.....thousands of years combined experience. I see over 200 years alone between Joe Reeves, Racer, Pappy, and Mr. Scott.
 
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