Is this Dry Bowl or an alternative problem?

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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Is this Dry Bowl or an alternative problem?

Post by tgreese »

Your reasoning is correct, as far as it goes. There has to be something missing in the discussion. I still maintain that siphoning backwards is not possible, considering the shape and position of the fuel path.

Evaporation is indeed a problem for many carburetors, and suggests some other path of escape for the fuel. A clamp on the fuel line stops both air and fuel in both directions. You are assuming that retrograde fuel flow is the cause of dry bowl, but the clamp affects more than that. And a single trial is not proof - you need to try it again under different conditions. Maybe your clamp is blocking air from going into the float bowl?

Try the one-way valve and see if it helps.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

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marc
Posts: 178
Joined: Tue Aug 11, 2020 8:24 am

Re: Is this Dry Bowl or an alternative problem?

Post by marc »

Tim, in fact, I have clamped the fuel return twice and both times it started right up in the next morning . As for air entering the carb via the fuel return, I looked into the other BBD carb I have, the one on the bench. The float bowl chamber is ventilated via the apperatures that the metering rods pass through, see pic, If gas is leaking out of the carb, the carb would not need draw air throuh the return.Mard
J10 1984, very stock with AMC 258.
Truck appears to have been rebuilt or restored at one time

Topic author
marc
Posts: 178
Joined: Tue Aug 11, 2020 8:24 am

Re: Is this Dry Bowl or an alternative problem?

Post by marc »

Too tired last night, forgot the picture. It shows the aperture the metering rod passes through above the float bowl. Assuming the BBD carb on the J110 works the same way as the 8434 I have on the bench,the float bowl vents into the chamber above the float bowl which opens to the interior of the air cleaner. If it is a leak in the carb bowl loosing gas, it must be slow, takes all night, so closing the fuel return shouldn't make a difference, air can still enter to allow fuel to leak out. It won't hurt to run a third test to confirm it.
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J10 1984, very stock with AMC 258.
Truck appears to have been rebuilt or restored at one time

Brynjaminjones
Posts: 3
Joined: Fri Jun 16, 2017 9:18 am

Re: Is this Dry Bowl or an alternative problem?

Post by Brynjaminjones »

I've recently been battling a similar issue with my 1991 GW. If the carb bowl is full, it will start great.

The bowl would evaporate quickly though, so within a day or so (depending on temperature) the bowl would be empty, then take loads of cranking to fill the bowl and start again.

I've finally solved mine, and it was as simple as replacing the fuel line from the tank to the fuel pump. My '91 has rubber at each end, connecting to a metal line.
I replaced the rubber at both ands and made sure it was clamped on tightly. It hasn't stopped the bowl from going dry, but it now takes about 3 seconds of cranking to fill the bowl, instead of about 30+ like it did previously.
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TUDrewser
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Location: Mesa, AZ

Re: Is this Dry Bowl or an alternative problem?

Post by TUDrewser »

Similar issue. Watching with anticipation...
1990 GW "saved by Jerry" edition
will e wrote:I guess life is better if you are not moving too fast.
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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Is this Dry Bowl or an alternative problem?

Post by tgreese »

Another possiblity: both the bowl is drying out (some?), and the fuel supply line is draining completely back to the tank. Once the bowl dries enough that the float drops and admits air behind the needle, the line can siphon back to the tank. With an empty line, it will take some cranking to fill the line and bring more fuel to the bowl, especially if the fuel pump reed valves are a bit leaky.

If the line from the tank is full, that will give an immediate shot of fuel into the bowl with the very first crank, which may be providing the quick starting you're noticing with the clamp.

A possible test would be to clamp the line at the float bowl, and open the line between the pump and the carburetor, allowing the expected drain-back to the tank, while holding the bowl charge whatever it may be. You could also use a straw or thin wire and put it down the metering rod to test the fuel level in the bowl. The pool of gas in the float bowl is supposed to be at atmospheric pressure - the carb uses the negative pressure of the engine vacuum to move and meter the fuel - so there should be a passage between the air horn and the float bowl. The air cleaner seals that area to some degree, raising the vapor concentration in the air and slowing evaporation. The bowl will evaporate much faster if you leave the air cleaner off, or use a large open-element air cleaner.

I mention this because the YF 1V (and maybe the BBD 2V?) for Jeeps should have a seal around the lifter link for the accelerator pump. This is a source of slosh and evaporation when missing on that app (often missing in the cheap rebuild kits). If your metering rod top is open to the outside air, it probably should not be. A connection to the air horn is probably ok.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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