Choke must be on or 5hp dies

brewster16

Well-Known Member
Aug 9, 2009
1,442
Long Beach Island, N.J.
Boat Info
'07 44 Sundancer
Engines
Twin Cummins QSC 8.3
First time using the Mercury 5hp this season and after she starts and warms I usually push the choke all the way in and just accelerate with the throttle. This year I have to keep the choke partially on (pulled out) in order to keep the dinghy going. Push it in like I usually do and she stalls right out. Anybody have any ideas on what to do?
 
Clean and dip the carb and the jets. It's easy, but you can't cut corners. Those little carbs are sensitive and even a little varnish or crud will cause the idle problems you describe. Soaking helps a lot, but don't soak any rubber parts, which includes the bowl gasket and the tip of the float valve.
 
If this is a 4 stroke...

There is a small brass plug that you can drill out to get to the ONLY adjustment screw for the fuel /air mix. YouTube has some videos on how to remove the brass plug.


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I had a 2 stroke 5hp that had similar symptoms. Turned out that the switch for fuel flow to come from the internal tank or the fuel line was the problem. It had some type of metal mesh that had turned to metal MUSH and was blocking the fuel flow. I removed the valve and cleaned out the bits of metal and replaced the little in line fuel filter and the motor ran like a champ again. Fuel starvation was the problem. Never bothered replacing the mesh. Always used the internal tank but used this valve as a "shut off" for the engine's fuel.

Hope yours is as easy!
 
My external tank line was full of crud! The ethanol gunked up. I pulled the connector to engine off the line and saw it. I proceeded to cut the line back to were there was no more sediment and it has been fine. Must have built up over time.
 
Mine did the same thing. I cleaned the carb and it still did it. According to the Mercury manual you "never use a wire to clean the jets." Well, I finally took it to a mechanic who used a wire to clean the jets and it ran perfectly.
 
Ducking as i prepare to get pummeled, but my new Coleman outboard, everybody including the outboard mechanic at my marina and the service manual say the ethanol will kill these motors. EVERY time i use the dingy, at the end of the day, i shut off the fuel valve and run it till all the fuel is out of the carb and it dies from lack of fuel. every.single.time. Told by many this will prevent issues down the road.
 
Let the pummeling commence!!!!

Naw, but I will add a few asterisks:

*killing the motor is a little dramatic, but cause grief? for sure.

*running ethanol out before storage helps, but a better idea is to not use it in the first place.
 
Ducking as i prepare to get pummeled, but my new Coleman outboard, everybody including the outboard mechanic at my marina and the service manual say the ethanol will kill these motors. EVERY time i use the dingy, at the end of the day, i shut off the fuel valve and run it till all the fuel is out of the carb and it dies from lack of fuel. every.single.time. Told by many this will prevent issues down the road.

Just remember, if it's a 2 stroke, every time you do that, you are starving the engine of lube.
 
Seeing e10 has been here since 1990 and most have adapted well, I concur what the many have told you. Fear not.
 
Mine is 4-stroke, you are right on 2 stroke though. we cant avoid ethanol, in Maryland it is at every gas station, none exempt.

That's probably for on-road vehicles? Have you done a search for recreational fuel?

In the Great Lakes we can easily find e-free fuel at marinas.

I just bought a new power washer for the house that came with a label forbidding even e10. There's a gas station not too far away that offers Rec90. It's double the price of mid-grade, but if the carb is happier with that than all my other small motors have been with e10, I'm good.
 
Good to throw some seafoam in the tank regularly, and in the oil one as well for 4 stroke ones
 
Ducking as i prepare to get pummeled, but my new Coleman outboard, everybody including the outboard mechanic at my marina and the service manual say the ethanol will kill these motors. EVERY time i use the dingy, at the end of the day, i shut off the fuel valve and run it till all the fuel is out of the carb and it dies from lack of fuel. every.single.time. Told by many this will prevent issues down the road.
This is what my service tech for the outboard told me also. After I started I have 3 years of care-free one pull starting.
 
The problem with every new small engine is that they are tuned for emissions rather than reliability. Lawnmower, snowblower, string trimmer, outboard motor, all of them run too lean out of the box.

often there will be some tiny speck in the fuel system somewhere right out of the box and that is all it takes.

I’m so sick of the extent environmental regulation goes for marginally better emissions at the expense of proper operation.
 
+1 on always running it dry before storage. I do this with all my small engines; weed trimmer, chain saw, lawn mower, etc. Having to run with partial choke is a sure sign of a gummed up carb.
 

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