My bowl runneth over!

[halmc]

OK, my luck is runing good this AM so lemmie try another question.

The engine mentioned in my model number post is a 2005 mercury four stroke 25hp.

My engine does not surge. It does the opposite of surge: that is, I can be honking along at any rpm and periodically, the engine temporarily floods with gas, clears out, and picks back up to the former rpm.

Once in a while, it will flood so bad that the eninge stops. How do I know that it's too much fuel, rather than fuel starvation? Cuz fuel runs out of every nook and cranny of the carb.

Pretty clear to me that the bowl is receiving waaaaay to much fuel from time to time.

I have had the carb apart twice chasing this problem and to my intense chagrin (and the intense anxiety of my pax) I've made it worse on both occasions.

Assuming it was trash preventing the viton-tipped vloat valve from closing properly, I cleaned and recleaned that area. I have also inspected the needle with a jewler's loupe and have seen nothing wrong.

In getting fuel to the bowl on this carburetor, the fuel passes from the fuel inlet on the bowl through the carburetor bowl gasket, thence up into the needlevalve, then to the bowl.

I'm gonna replace the needle valve this time, but wonder whether it's worthwhile to replace the bowl gasket as well on the theory that the gasket is permitting fuel to pass into the bowl on the way to the needle valve?

I suppose the answer is obvious, and I'm gonna replace the gasket, but I do wonder if anyone has ever had the bowl gasket fail in this way.

BTW, the float level on this -- and on most modern carbs -- ain't adjustable.

Thoughts?

 

[Maxz695]

Re: My bowl runneth over!

Does the float have a spring on top to close the needles? I do suppose you cleaned the float bowl and there is no gunk resrickting the float from riding up the guide pin. What is the condition of the float. small chance but the spring may be lodged to far into the float and gummed up or something causing the needle to just barely close sometimes and not close at others.. There should be enough pressure to keep the needle vavles tighly close when full not just somewhat closed. This is the best way I can expain fuel flowing intemintenly more and less to cause this.

 

[carholme]

Re: My bowl runneth over!

The manual still calls for a float height check:

Float Height
0.47-0.63 in. (12.0-16.0 mm)

If you are getting flooding to that extent, it would be worth checking.

Gerry

 

[CharlieB]

Re: My bowl runneth over!

Pull the dipstick and check the oil level.

A pinhole in the fuel pump diaphragm will flood the crankcase with fuel. While running, blowby the piston rings will cause that fuel/oil to blow into the carb intake, flooding the motor.

 

[halmc]

Re: My bowl runneth over!

Good suggestions all, I'll follow up on each one. But what about my gasket question. Anybody ever had one fail such that it was losing fuel into the bowl?

 

[oldman570]

Re: My bowl runneth over!

Anything is possable when carbs have been worked on. This even includes from the manufacture as some of thier motors are used in the trainnig of techs at factory schools and then sold thru outlets as used motors. I have had bowl gaskets leak fuel after rebuilding the carb. I now bench test the carbs before replacing them on the motor to make sure there are no leaks and the inlet needle will seat and cut off fuel flow then drain the bowl and see that the float will lower and let fuel into the bowl. I use a tank, hose with primer bulb, and connect it to the fuel inlet on the carb for the testing. Save unnessary placement and removal on the motor if things are not right. JMO
Oldman570

 

[Maxz695]

Re: My bowl runneth over!

If the gasket is in good shape it sould work fine. The problem lies when there is too much fuel in the bowl It has to find a way out somehwere due to fuel pump pressure. Kits are cheap and available. I woud sugget a full kit. Someone may have put the wrong needle and seats as well as other items such as jets mixture screws etc. This should solve you issues

 

[halmc]

Re: My bowl runneth over!

Thanks for the additional suggestions. I did order a complete kit, mindful that the previous owner noted that the carburetor "might need some work" which indicated to me -- consistent with your theory, Maxz695 -- that it might have already received some.

Oldman570, last time I hung over the RH pontoon on my boat, removing the carb from the engine, hoping to drop neither parts nor tools overboard, I promised that I would bench test the carb before I again installed it. That's a good suggestion and I'll follow it.

 

[CharlieB]

Re: My bowl runneth over!

Pontoon, tie it up back-end to the dock, sit and hang your legs over the edge of the dock with a towel laid out alongside you and another across your lap and tucked into the side of the motor, have the motor turned off to the side.

Get busy.

A couple of BIG float to keep any waves from bouncing the motor to hard off your legs.

 

[halmc]

Re: My bowl runneth over!

LOL, Off my legs would be the least of my worries as I straddled the engine.

Really, really close inspecton of the bowl gasket shows some traces of silicon seal, so I suspect I'm not the first to encounter this issue with this motor -- and probably not the first cheap skate to try to avoid buying the whole carb kit.

I wish I had back all the money and other resources I've spent trying to save money and other resources.

 

[Maxz695]

Re: My bowl runneth over!

That would be something to start over knowing we we learned along the way!! :nightmare:

 

[halmc]

Re: My bowl runneth over!

Epilogue: about 98% of the surging was cured with a carburetor kit. Upon very close inspection, the old bowl-to-body gasket was hard and flat, probably wasn't making a good seal, permitting the pressurized fuel to leak into the bowl. Either that, or the float valve was more worn than it looked. If I had it to do again, I would not buy the kit, as the gasket and the float valve are the only useful parts of the ~$50 kit and together they cost about $30. I'm attibuting the last 2% of uneven running to idle mixture adjustment.

 

[Maxz695]

Re: My bowl runneth over!

Sight unssen It is hard to determine the main jet the mixture scew Float levers if aplicable. Therefore I recommended a full kit so you would have all nessecary parts as I have in the past tryed to get a few parts here and a few parts there and the shipping cost alone was more than the entire kit. True you may have got lucky In just getting a needle and seat and bowl gasket. but then again sight unseen It wouldn,t be my best guess as the right thing to do. Glad to hear the engine performance has improved.

 

[halmc]

Re: My bowl runneth over!

True you may have got lucky In just getting a needle and seat and bowl gasket. but then again sight unseen It wouldn,t be my best guess as the right thing to do.

I would agree on an old carb with lots of gaskets and adjustments, but on a modern carb where there's one gasket and a fixed float level, well, not so much.

Not a big issue tho. In fact I did order the full kit out of the same considerations you list.

 

[Maxz695]

Re: My bowl runneth over!

Did the full kit come with new venturies? The black plastic venturie sits on the main jet in the carb throats. I had to buy a set of replacement carbs off ebay as one of mine broke and I couldn,t find it anywhere. View attachment 180139View attachment 180140. They get old and brittle. Having a few spare carb parts is always a good thing, and may come in useful in the future and save lots of time and money as you will already have them. JMO