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As discussed some in the "Parrakeet reassembly" thread I'm having some fuel flow issues. Part of it is the geometry causing insufficient fuel flow at WOT, less than a half tank, and high AOA, but it also seemed to be starving for fuel in level flight... so I decided to look into the carburetor. I disassembled it last night and tried to set the float level this morning.
Seems like I must be missing something, but if so I can't see what it is. I set up a rig to provide the proper head pressure to set the float level. A quick sanity check with a ruler showed the level to be too high by about 5/32" (it should be 13/32, it was more like 1/4", or 8/32).
I then made a gauge to set it properly, and removed the seat. There were four gaskets underneath, totaling .090". According to the Stromberg manual, adding 1/64" of gasket will lower the float level 5/64, I had to move it 5/32 or 10/64, so an additional 1/32" would be needed for a total thickness of .120. I built that up with a combination of the old and new gaskets, and... couldn't get the float pivot pin in; with the bottom of the float hitting and the needle seated in the seat, the pivot in the float arm was too high above the hole in the carburetor body.
I went back to the original (total .090) gaskets and reinstalled the float, and again checked it, this time with the new gauge... same results. In addition, the needle travel, which is supposed to be .048" minimum, was more like .020, which explains why I couldn't get the pivot pin in with the thicker gaskets.
Closer examination showed that the float is hitting the main jet well before the needle has reached its full travel.
Float down/needle open:
Float up/needle closed:
Note that the above picture shows the float "up" and the needle closed... where the fuel level (and thus the float) is still 1/4" too high. But there's no room for the float to move down 1/4". (That's not a blob of solder restricting travel as somebody else suggested, it's just a reflection from the shiny spot where it hits the jet.)
The jet isn't shown in the section view above, but the centerline to the left of the needle seat shows where it is... only the float is much closer to the seat than shown there. The tab shown on the bottom of the float which I presume is to limit the float travel is present on mine, only mine is much shorter (barely visible in the photos), doesn't stick out as much, and doesn't hit anything anyway before the float contacts the jet.
I've been unable to unscrew the jet, and I don't want to damage anything by forcing it.
I wondered if it could be the wrong float? But I don't see how that could be. The carb came with the engine which came out of a Cub, where it was supposedly running fine... for that matter it was running mostly OK in my Parrakeet, except for the fuel flow issues at full throttle, well, that might make sense if the needle couldn't open far enough. (The fuel flow issue at full power in a steep climb was a known issue, but I was finding it eventually starved at full throttle even in level flight.)
A too-high float level might also cause the carburetor to drool on the ground, as mine does, but a less than perfectly fitting needle would also cause that.
The carburetor (body, at least) is the correct one for my engine, and it has the Delrin needle, the required added weight on the float arm, and what appears to be the correct seat.
There's about .010" of play at the float pivot, which means about .0125 of lost motion at the needle. By raising the seat .010 and pressing down on the inner end of the shaft with a screwdriver, the level is within tolerance... but there's nowhere near the required .048 needle travel when the bowl is empty.
Seems like I must be missing something, but if so I can't see what it is. I set up a rig to provide the proper head pressure to set the float level. A quick sanity check with a ruler showed the level to be too high by about 5/32" (it should be 13/32, it was more like 1/4", or 8/32).
I then made a gauge to set it properly, and removed the seat. There were four gaskets underneath, totaling .090". According to the Stromberg manual, adding 1/64" of gasket will lower the float level 5/64, I had to move it 5/32 or 10/64, so an additional 1/32" would be needed for a total thickness of .120. I built that up with a combination of the old and new gaskets, and... couldn't get the float pivot pin in; with the bottom of the float hitting and the needle seated in the seat, the pivot in the float arm was too high above the hole in the carburetor body.
I went back to the original (total .090) gaskets and reinstalled the float, and again checked it, this time with the new gauge... same results. In addition, the needle travel, which is supposed to be .048" minimum, was more like .020, which explains why I couldn't get the pivot pin in with the thicker gaskets.
Closer examination showed that the float is hitting the main jet well before the needle has reached its full travel.
Float down/needle open:
Float up/needle closed:
Note that the above picture shows the float "up" and the needle closed... where the fuel level (and thus the float) is still 1/4" too high. But there's no room for the float to move down 1/4". (That's not a blob of solder restricting travel as somebody else suggested, it's just a reflection from the shiny spot where it hits the jet.)
The jet isn't shown in the section view above, but the centerline to the left of the needle seat shows where it is... only the float is much closer to the seat than shown there. The tab shown on the bottom of the float which I presume is to limit the float travel is present on mine, only mine is much shorter (barely visible in the photos), doesn't stick out as much, and doesn't hit anything anyway before the float contacts the jet.
I've been unable to unscrew the jet, and I don't want to damage anything by forcing it.
I wondered if it could be the wrong float? But I don't see how that could be. The carb came with the engine which came out of a Cub, where it was supposedly running fine... for that matter it was running mostly OK in my Parrakeet, except for the fuel flow issues at full throttle, well, that might make sense if the needle couldn't open far enough. (The fuel flow issue at full power in a steep climb was a known issue, but I was finding it eventually starved at full throttle even in level flight.)
A too-high float level might also cause the carburetor to drool on the ground, as mine does, but a less than perfectly fitting needle would also cause that.
The carburetor (body, at least) is the correct one for my engine, and it has the Delrin needle, the required added weight on the float arm, and what appears to be the correct seat.
There's about .010" of play at the float pivot, which means about .0125 of lost motion at the needle. By raising the seat .010 and pressing down on the inner end of the shaft with a screwdriver, the level is within tolerance... but there's nowhere near the required .048 needle travel when the bowl is empty.
