Need some serious help with my 1993 20hp 2stroke merc

Ok,so here is my issue.I go to the lake today and my outboard runs great at idle,got all the tuning great and here we go to wot and 15 seconds later it stalls.To make a long story short because i'm so frustrated and i'm hoping someone else has had a similar issue so i can get help.Here is my issue.When i go wot it wants to stall unless i constantly keep pumping the bulb and then it never stalls out.I tried 2 different new lines and tanks and got the same issue.It runs like a raped ape but it won't stay going unless i constantly keep pumping the ball.I have replaced all the gaskets in the carb,the carb is in mint with no varnish or old parts except there is a plastic fuel pump that is obsolete and a spring release valve that i can get but only in a repair kit for $90.Now i don't mind spending the money but i just don't know if that's the issue.Everything fuel related is brand new on this outboard including the tank and line.

I went to my local marina and they couldn't even answer me and tell me a round about what it could be but that release spring valve that i guess acts as a vacuum to suck the gas in,The lady i know well there said if the plastic part was bad it would leak gas.So i ask for any help please because i love this outboard and i don't know what to do as of now.I don't know what else it could be.

Don't laugh but after I bought my first boat the same thing happened to me . . . I FORGOT TO OPEN THE TANK VENT

That is open,believe that.I am so lost here.I'm so frustrated and may be stuck with a beautiful outboard i can't use.I'm not bringing it to my local marina because they said it's a waste.I don't know what to do.I'm hoping someone can help me here.

have you taken the fuel pump apart and inspected it?

Same thing was happening to me.

I had a glob of something in the gas tank. It would suck to the hose and stop the gas flow.

Took me four trips to figure it out.

Everything on the carb is brand new,yes i took the fuel pump apart just an hr ago and nothing seemed out of wack.Now there is like a spring under the gasket that i believe is like a valve that seems like it's working fine.The funny thing is i used 2 brand new tanks and lines and got the same results,starving for fuel,now it's even running like crap and stalling in idle on muffs,strange stuff.I ran near 30 minutes going wot and it ran like a raped ape but if i let off the primer ball for more then 5 seconds it would stall,this is probably something so darn simple but i just can't figure out what it is.

have you thoroughly inspected the fuel line and connections (clamps etc) from the engine side of the fuel line disconnect to the fuel pump? Perhaps there is a slight leak there and its sucking air. Since its sucking fuel you may not see a leak. Or maybe the inside of this line is deteriorating and is causing a flow blockage?

Another thing is you are absolutely certain there is not a pin hole or minute crack in the fuel pump diaphragm?

just throwing out a few ideas

Everything is 100% brand new as far as lines,gaskets,etc.I checked it again today and i saw no daylight in any gaskets.I'm going to have to revisit the carb and check over everything once again step by step.The most frustrating thing is it runs so freaken awesome, i just can't get it to open up more than 15 seconds at wot without pumping the ball.I put a whole new carb diaphragm kit in just a month ago.I guess what i must do is tear down the carb again and inspect it all again.Would like the needle cause this,or like the float,or jets,anything else but like a air leak as you said or pin hole in one of the gaskets.I put everything back together as it should be.I will retrace everything like i said.

I bet it's something so stupid and easy.I can't seem to find the fuel pump for this outboard,it's obsolete,so i don't know what to do there.This is crazy.Maybe it's a defective male engine gas connect that i just put on the engine a month ago.All i know is when i pump the ball on either of the 2 brand new tanks or line i use it would get rock hard then in time it just seems like it goes limp unless i keep pumping it.

If it had an air leak wouldn't i see a gas leak somewhere?

It's also starting to run all over the place on muffs now,stalls and then it is hard to restart.The thing i noticed is the primer plunger when pressed is it supposed to get hard?Also when i drained the fuel lines on the engine and the fuel filter and hit the primer plunger button i could here air going into the carb because there was no gas,is this normal?I guess i need to take the carb off and inspect it all again.

Take off the carb and look at the gasket. If the hole in the gasket and the hole in the head don't match then your fuel pump won't work. Ask me how I know.....

I'm wondering if it's the fuel connection on the engine itself.Now i did just replace it less than a month ago but whats the chances of a new one being bad by sucking air?

So i did some research and it said to put the gas tank much higher than the outboard and if it keeps running and doesn't stall it's the fuel pump.The only thing i didn't replace is the plastic hard body with is NLA and the spring valve in the fuel pump.I'm going to go over everything today again,rip the carb off,make sure there isn't anything in their again,check all lines,i have to eliminate everything one by one.I may run a can of seafoam with 3/4 gallon gas to see if it clears up and stays running if maybe the needle or float is stuck,if that doesn't work,carb tear down time.

since it now running erratic its sounding to me like you have a vacuum leak someplace.

It ran fine before installing all new gaskets,now it starves for fuel,so it's either something I installed that is defective or I don't know.

scoobeb said:

It ran fine before installing all new gaskets,now it starves for fuel,so it's either something I installed that is defective or I don't know.

Click to expand...

define "all new gaskets"

Whole carb repair kit

I bet it's the needle sticking restricting the float from letting gas in. Yesterday we tried to empty a fuel line and when we stuck our finger in the fuel fitting trying to gavity feed it to the engine it was spitting gas back out at us instead of towards the engine,to me that sounds like the needle is stuck.

if that is what you think take the carb off

take the bowl off

blow (with your mouth) into the fuel inlet and try working the float up and down and see if it is working properly

...or...

while its still on the motor, shake the heck out of motor and see if you can unstick the needle. If that does something then you know you its sticking

I'm going to run seafoam through it to try and clean anything out if in fact that's what it is.

I have the same motor, albeit a few years older, and I ran into the same problem.

You mentioned replacing the fuel fitting on the engine side of the fuel connection. By chance is it a grey plastic part now that you sourced from a local Walmart or as part of an Attwood hose connector kit. For some reason (don't ask me why) there are kits out there with two connectors, a female connector that goes at the end of the hose and a connector that looks just like the male Mercury "Engine Side" connection -- only it's actually a different version of the "Hose Side" connector, so the check valve operates in reverse of how it needs to when mounted on the motor vs. the fuel hose. Put this on the motor side and it will block fuel flow to the motor. Your pressure on the fuel bulb may be opening the valve and allowing fuel to get through until the pressure dissipates - the tiny fuel pump on the side of your motor does not pull enough vacuum to open the valve without pressure in the fuel line side of the equation.

I know this sounds crazy but you aren't the first person on here to do this if you did. I didn't notice it testing the motor on the earmuffs either because it really isn't using that much fuel during the tests. I was in the same boat - rebuilt everything and was all excited to get going & then WTF!!!

I use a clear fuel line from my fuel filter to my carb so I can see the gas flowing. If you've got the same great - start your motor with the cowl off and you should see fuel sitting in the line from the carb to the filter - this should noticeably flow when the engine is running (even at idle at the dock.) If you notice this line is dry then you're not getting fuel. If by priming the bulb you see the fuel again flow from the fuel filter down & fill the line you know this is the issue.

If you're using solid fuel lines and don't want to replace them get a double barbed fitting from the local hardware store and remove both the engine side connector from the fuel line going to the carb and the connector at the end of the fuel line coming from the tank and hook both to the barbed fitting creating a direct connection to the tank (but no quick-release). Prime as you normally would until there is pressure in the line & you should be good to go.

Assuming that fixes it then the only thing you need to do is get the correct mercury/mariner engine-side connector or rebuild your old one.