Attached is the temperature log for the carburetor internal temperature - measured with a probe in the vent tube; the file is in text format (*.txt) rename it to *.csv format and it will open in excel or other spreadsheet software. CK5 will only allow attaching txt format not csv?
Also, not directly related to accelerator pump, fuel evaporating, and hard starting after a few days - but after I carefully filed the airhorn flat during the last carb teardown (point of teardown was just to remove the hook from the needle and float) I now have idle adjustment again (I thought is was because I don't have the vapor canister port connected - I replaced canister with a rollover shutoff valve). Previously, I had to turn the idle screws nearly all the way shut to get a vacuum change. Now I have adjustment again in the midrange of the idle screws. I managed to get 16.5 in-hg at 600rpm idle. Driving last night - before adjusting idle - seemed smoother and more responsive. Acceleration seemed to pull better though I did not get into it too much, just a short blast on the on-ramp. At the next fill-up I will see if I gained any fuel mileage - passed-up a $2.75/gal sign on the way to the in-law's thanksgiving, that was nice to see.
Back to the carb temp: I've previously posted the air temp inside the air cleaner, the air temp near the firewall, and the fuel temp. I wanted the carburetor internal temperature so I put the datalogger probe down the fuel bowl vent. I'd expected the carburetor to be a source of heat due to contact with the intake manifold; I expected something close to 185 deg F. The carburetor during freeway cruising is in the low 70s. Colder than the intake air ~ 100 deg F or fuel ~ 100 deg F. It makes sense now, the air passing through the venturi is compressed and then expands passing through the butterflys, absorbing heat, and reducing the temp, I read that it is usually a 30 deg F drop; 100 deg F air will drop to 70 deg (can cause icing in some situations). What I did not expect is that this significantly cools the carburetor body. Meaning, both the fuel in the bowl and the air entering the carb is cooled not heated.
I am going to drive this for a couple tanks of fuel - get some mileage readings and see if removing the hook from the needle stopped the fuel backflow/evaportation several days sitting hard starting problem; the idea is the fuel evaporates some and drops the fuel float, opening the needle and allowing more fuel to siphon out, and then more fuel evaporates - without the hook the needle stays seated. Next, I will add a wood thermal spacer under the carb and then add a heat shield between the headers and fuel line. This will cool the carburetor further and cool the fuel.
Notice in the data the heat soak at shutdown. The carburetor went from 70 deg to 110 deg in the next half an hour. That is fuel evaporating during that time. It took five hours to cool back down to 70 deg F. And, it was cold out, during the drive it was in the mid 50s and dropping, after shutdown it was in the high 40s and by midnight it was in the low 40s. How long the engine retains heat continues to surprise me.
