Gushing carb...

[jeff_smith_0423]

Evening again. Thanks to all of the suggestions on this forum, i got the carbs put back on my Merc 850 tonight, fuel pump rebuilt, fuel lines installed, and get this.. IT RUNS!

After screaming up and down the driveway, i took a closer look.. I think i've botched something. When i prime the engine, fuel literally pours out of the bottom carb's venturi, fuel bowl jet vent, and the vent directly in front of the venturi/nozzle.

It also pumps fuel directly out of the same places while running, collecting in the lower cowl. Obviously i've botched something. When i tore it down to clean it, i did not remove the float /arm assemblies because i could not remove the pin. I also didn't remove the nozzle, venturi, and fuel bowl jet vent because they were quite stuck and my efforts to unscrew them were met with the creaking of brittle metal. Rather than push my luck , i left them in place and gave them a good cleaning with gumout and compressed air. This seemed to work fine on the upper carb - no signs of any leaking.

It would appear that it's not a blockage since there's fuel flowing EVERYWHERE, but i don't know what to look for when i remove and dissassemble. Any old pros out there have suggestions?

Getting this thing running has been quite a rewarding experience - and it's come together in very short order thanks to all of the suggestions and information i've found in this forum. Thanks again!

 

[Silvertip]

Re: Gushing carb...

The fuel inlet needle is operated by the float. When the engine uses fuel from the float bowl, the float drops which opens the inlet needle and seat and the fuel pump refills the bowl until the float rises again and shuts off the flow. You have either inserted the needle upside down, forgot it entirely, its hung up, not sealing, or the float level is incorrectly set or is hanging up. It must be disassembled to correct it. Before you button up the carb, tip it upside down and blow (by mouth) into the fuel inlet. If air flows, you still have a problem. If not, it's good to go. Float level must be properly set. Set it too high and the fuel will never shut off.

 

[jeff_smith_0423]

Re: Gushing carb...

As i did more searching around the forums, i've come to the same conclusion. When i put this needle in, i thought it felt a little loose. I'm betting that's where i screwed up. I'll probably order another matched set just to be safe.

 

[j_martin]

Re: Gushing carb...

As i did more searching around the forums, i've come to the same conclusion. When i put this needle in, i thought it felt a little loose. I'm betting that's where i screwed up. I'll probably order another matched set just to be safe.

You probably forgot or dropped the gasket under the seat.

hope it helps
John

 

[Silvertip]

Re: Gushing carb...

As I read your first post again, I noticed that you said you didn't remove the float. If that's the case, how did you get the needle and seat out? If you bent the float to get those parts out, that may be the cause of the problem if you didn't reset float drop and float level. Float drop is critical only if it's set so low the inlet needle can fall out which would account for the gushing carb.

 

[jeff_smith_0423]

Re: Gushing carb...

the float hinged one way, the float arm hinged the other way, and gave me access to the needle and seat without removing them. I was exceedingly careful not to bend either out of adjustment while removing the needle and seat but who knows. I just tore it down again, checked the needle positioning, and it was "hanging out" a bit in the seat. I popped it in till it hit bottom, reassembled, and gave it a mouth pressure test.. I can still hear air coming out of the fuel bowl jet vent. But, either because i'm an indiana idiot or i hate gas in my mouth, i didn't perform the same test as a "control" before i tore it apart.

I'm trying to find something i can measure the float set with so i can tear it down, check the float height against spec, and try it again. Where is some thin, rigid cardboard when i need it!

It's almost become comical. I've gone through about 3/4 gallon of fuel in about 20 combined minutes of priming, starting, and idling. I'm going to have to go buy fuel before i can test again! The garage smells like heaven. The house, not so much.

 

[Don S]

Re: Gushing carb...

Did you put a new needle and seat in it when you had it apart? Did you check the float level and did you make sure the spring was still in the float?

 

[jeff_smith_0423]

Re: Gushing carb...

Well, i have good news and bad. Looked at the float height, and it was pretty darn close - maybe a 16th off, so i let it be. Pressure tested and it didn't blow air. installed the assembly (hey i'm getting good at this!). Primed motor, could hear gas getting into the bowl. Pressed my luck and gave it another squeeze, the gusher returned.

So, at this point, i think the needle is bad. This one fits way looser into the seat than the other carb's needle did. Damn me for throwing away the old parts! I guess i'll see if i can source one locally, since shipping is more than the part.

 

[Silvertip]

Re: Gushing carb...

Sounds like an incorrect needle or seat made its way into the kit. Or, if you changed the needle but not the seat, you very likely have a compatibility problem. Needles and seats should be replaced as a set.

 

[jeff_smith_0423]

Re: Gushing carb...

Well, i was able to source the parts from Napa. A little more expensive than ordering, but no shipping charges and the parts were available within 24 hours. Tore it down, replaced needle, seat, gasket, measured float set with a ruled feeler gauge, reassembled, pressurized, and NO LEAKS.

Now, if i would have been smart and stored the battery indoors, I could test start it and begin getting it dialed in.

The frustrations never end

 

[achris]

Re: Gushing carb...

Any old pros out there

I resemble that comment!!!

Jeff,

Just be aware that the needles in those carbs unseat very easily. It's quite normal for them the open when squeezing the fuel primer.

Chris.........

 

[j_martin]

Re: Gushing carb...

I resemble that comment!!!

Jeff,

Just be aware that the needles in those carbs unseat very easily. It's quite normal for them the open when squeezing the fuel primer.

Chris.........

Like Achris said. You can get about 10 lbs pressure with a white knuckle grip on the primer bulb. About 7 or 8 can unseat the needle. Normal running pressure is under 5.

hope it helps
John