merc 20 hp 4 stroke carb issue

[ClemsonAlum]

1. Motor not peeing: Check to make sure the pee hole is clear. Dirt dobblers and other bugs will stop it up in no time flat. Run a wire or stick up it and spray a little water up in it.

2. Only starts on choke with carb cleaner: I have only worked on my 2 stroke, but if it was me, I would take the crab apart and clean again to make 110% sure the idle jet passage was clear. Soak with carb cleaner, run thin wire through all passages, clean again with carb cleaner spray (spraying the OPPOSITE direction of fuel flow) , and use compressed air.

-Kurt

 

[marlattrr]

Okay progress made tonight.

Water pump works great. No issues there. Did the bucket trick.

Used a new fuel tank i had with a new line. Still overflows the carb.

I can start it with choke on and squirting in carb cleaner. It will run if i turn the idle screw up and it runs at very high idle. If I turn the screw down to a normal idle it dies.

 

[RaisedByWolves]

Are you using a tach or just going by ear?


I don’t think the carb cleaner is a good starting fluid, it actually might be bad for your engine, ie no oil.


Try to find a small squeeze bottle to dribble gas into the carb instead.

This can also help determine a lean condition via squirting fuel into the carb when it stumbles to see if it will respond.

I have never seen a tank like that, but IMO it shouldn’t be pressurized.

 

[marlattrr]

Thanks for all the help. The “slow jet” was definitely clogged. I cleared it up. It runs much better but still not quite there. Will idle off of choke now and it’s restarting.

When i roll to the throttle it bogs down and dies if i do it too fast. If i bring the throttle on slow it will stay running. Seems like i really need to open it up on the water.

Still dumps gas while its running though. :?:

 

[RaisedByWolves]

Thanks for all the help. The “slow jet” was definitely clogged. I cleared it up. It runs much better but still not quite there. Will idle off of choke now and it’s restarting.

When i roll to the throttle it bogs down and dies if i do it too fast. If i bring the throttle on slow it will stay running. Seems like i really need to open it up on the water.

Still dumps gas while its running though. :?:

That’s a headscratcher, but the dumping fuel is why it’s stumbling when you open the throttle.

It’s loading up and there is extra fuel getting sucked out of the crankcase with the sudden intake rush.

Go back to basics, float height, needle seat, maybe find a breakdown of the carb and go through it piece by piece.

 

[MrGiggles]

Quick troubleshooting tip, when it's acting up, bump the choke. If it takes off, not enough fuel, if it bogs worse, too much.

 

[marlattrr]

Tried again. No luck. It has to be my float. The motor is running now but fuel still dumping.

Is there any way I could of knocked the float level out? This one doesnt seem adjustable. The service manual says replace float if out of spec. This one and the needle are brand new.

Theres also a brass seat where the needle valve sits. Is there a way to get that out?

 

[ClemsonAlum]

Yes, that needle seat should screw out. Use a large flathead that fits, or you will strip the brass. Clean it good to be sure there is no crud keeping the needle from seating right. Look at the rubber tip on the needle. Make sure there is no groove warn into it.

-Kurt

 

[marlattrr]

The float needle seat on the right doesnt have a flat groove for a screw driver

 

[RaisedByWolves]

Tried again. No luck. It has to be my float. The motor is running now but fuel still dumping.

Is there any way I could of knocked the float level out? This one doesnt seem adjustable. The service manual says replace float if out of spec. This one and the needle are brand new.

Theres also a brass seat where the needle valve sits. Is there a way to get that out?

You may have a waterlogged float.

I don’t think that one is meant to come out, but it just might be missing the o-ring for the needle to seat on.

Double check your carb diagram.


Edit: for whatever reason the carb diagrams you posted weren’t showing on my phone.

Does not appear to use an o-ring.

 

[marlattrr]

I dont see a way to adjust the float height on this thing either.

Im stuck.

 

[MrGiggles]

Try holding the carb upside down and blow into the fuel inlet. Does it seal with gravity pulling the float down?

You can also lightly clamp the carb in a vice and gravity feed it with a bottle.

If the float was waterlogged you would be able to tell by shaking it, there should be no liquid inside. It's not on upside down is it?

That seat is not replaceable, appears to be pressed into the carb body.

 

[marlattrr]

It does seal with gravity when i hold it upside down. Needle is brand new and float brand new.

It fires right up now and will run but only with the idle up high. It runs better with the choke on. With choke on or off it dumps fuel out the overflow.

Seems like it would run the water but id constantly be dumping fuel.

 

[RaisedByWolves]

Is the float level with the carb body when the carb is held upside down?

The method to adjust a float is to just bend the little metal pivot tab that connects the float to the pivot.

 

[ClemsonAlum]

What he said ^ . Also is the float needle attached to the float with a mini cotter pin? Maybe needle is getting stuck in up position? Not sure if those carbs have the little pins?

-Kurt

 

[marlattrr]

Its definitely level. I checked it.

There is no metal tab but when upside down i can blow into the fuel inlet and cant get air through.

Its not even a slow drip of gas when running its a constant drip.

 

[marlattrr]

Im almost ready to just buy a new carb.

 

[marlattrr]

Could something outside the carb like my fuel pump cause this?

 

[marlattrr]

What about the O-ring on my main jet?

 

[marlattrr]

Ordered a new carb on amazon for 108 bucks. At this point ive invested far too much time to keep going. :|