- Hey Folks,
On hot days (100-115 degrees) when I stop at traffic light, idle is initially fine but gradually, over 20-40 seconds deteriorates, drops and stumbles a bit and then after almost wanting to stall, it picks back up to normal, for about 20-40 seconds and if I sit stopped, idling (especially with AC on) it repeats this cycle again and again. Before I explain my observations, I will detail my fuel delivery configuration:
A-Stock type mechanical fuel pump that gives a steady 6 3/4-7 1/4 PSI.
B-Steel line from pump to a clear bodied fuel filter.
1-steel line is connected to the filter with a short length of rubber hose. The nipple of the filter basically meets/touches the steel line and the hose simply seals the connection.
C-Out of filter to a short steel line going into a QFT fuel pressure regulator, set to 5 3/4-6 PSI. Again, a short piece of rubber to seal the connection.
D-Out of fuel pressure regulator into a QFT-580VS carburetor (hard plumbed) with sight glasses on the float bowls.
So here is my test/observation sequence:
1-idling fine with AC on, engine well warmed on a hot day.
2-Fuel bowl level starts to visibly drop slightly.
3-Clear filter starts to get a few bubbles in ita-Idle begins to deteriorate.
4-Fuel bowl level continues to drop slightly.
a-Filter fills with bubbles.
b-Idle continues to deteriorate.
5-Fuel bowl slowly fills back up to normal level
a-Filter bubbles are gone
b-Idles improves back to normal
6-After 20-40 seconds this cycle begins and repeats, again and again, etc..........
Now I'm making a semi-educated guess that the problem is "boiling" fuel. My real question is, what process "exactly" is causing it and how can I cure it? Obviously heat is at the root, but is it:
A-Fuel under pressure from the float needle/seat closed having a higher boiling temp?
1-Float opens, dropping the pressure and thus boiling temp.
2-Bowl begins to refill slowly because of the boiling bubbles.
3-Float closes, thus increasing pressure/boiling temp.
Or do ya think:
A-Fuel in line gets to sit long enough to boil and then when the float opens.
B-The cooler fuel from the tank cures the issue?
Its sort of "which came first, the chicken or the egg" kinda question.
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What the actual cause is will have a significant impact on what the solution is.
Any and all thoughts comments and/or suggestions will be sincerely welcomed.
TIA,
Gene