POSTED BY PRO67CHEVY
"Hey All. Trying to get the chevelle ready for its debut trip to the drags. After playing on some back roads to see how the car handles, I found a severe bog after standing on the pedal for a few seconds.
Car info: 468 BBC with small solid roller, cast oval ports, performer RPM, and a 950 HP carb. TH400 w/ standard pattern, 12 bolt with 4.10s
Fuel system: Mallory Comp 140 pump and filter, return style regulator with 3/8" feed, and 1/2" return.
Dropped it into 1st, take it almost 6k, shift into 2nd, take that to about 6k, then I hit 3rd and a second later the car loses all power and nose dives down. I let off and it drives normal again.
I'm sure it's fuel. But where. I can't imagine the pressure needs to go up. It’s at 7psi now. I have a 3/8s feed line and a 1/2" return line. Don't know if the difference in line size affects anything. There's also a vacuum port on the regulator that I believe increases pressure at WOT, it's capped off but not sure if that is worth looking into. I don't think the pump is running dry but I did only have a 1/4 tank of gas. Carb issues? PV not working?
Thanks for Looking!"
thats a classic symptom of the carbs fuel bowls running dry because the fuel supply is not consistent.
this is far more frequent with the dead head fuel pressure regulators OR when guys place the return style regulator before the carbs inlet port.
obviously your fuel filter(s) and fuel line internal size and fuel pump volume and pressure, have an effect your results
Id suggest at least temporarily connecting a fuel pressure gauge at the carbs fuel inlet port so you can monitor the fuel pressure at that point during a race.
if the pressure falls at the carbs inlet port its a supply issue, if its consistent I,d be looking at a blockage in the fuel inlet ,especially if its got a brass in carb filter.
you might be amazed at what a few tests with a fuel pressure gauge can tell you
IF YOUR CURRENT FUEL PUMPS CORRECTLY SET UP AND FUNCTIONING, you should not have any problem, but a partly clogged fuel filter might also be a problem.
the fuel pressure gauge at the carbs inlet port should let you know what to look for.
QUESTION
How do I adjust the fuel level on my carburetor?
ANSWER Setting the fuel level should be the first thing you do before attempting to make any further adjustments.The float level should put the fuel level just below the bottom of sight plug hole. You will make the adjustment with the vehicle on a level surface and the engine idling. You will first remove the sight plug, then to make your adjustment you will need to loosen the lock screw on the needle and seat. This will allow you to turn the adjusting nut to raise or lower the float level. Each hex flat on the nut will change the float level approximately 1/32". When you have the fuel level just below sight plug hole you will then tighten the lock screw and reinstall the sight hole plug. Make sure you have a shop towel handy in case you have any fuel leaks from the Sight plug or needle and seat adjusting nut.
first step is always to verify both fuel bowls have the floats correctly set (EASY ON MOST HOLLEY CARBS WITH A SITE PLUG)
these brass inlet filters need to be replaced occasionally as they tend to restrict fuel flow
RELATED THREADS
viewtopic.php?f=55&t=211
viewtopic.php?f=55&t=1939
viewtopic.php?f=55&t=635
viewtopic.php?f=55&t=109
"Hey All. Trying to get the chevelle ready for its debut trip to the drags. After playing on some back roads to see how the car handles, I found a severe bog after standing on the pedal for a few seconds.
Car info: 468 BBC with small solid roller, cast oval ports, performer RPM, and a 950 HP carb. TH400 w/ standard pattern, 12 bolt with 4.10s
Fuel system: Mallory Comp 140 pump and filter, return style regulator with 3/8" feed, and 1/2" return.
Dropped it into 1st, take it almost 6k, shift into 2nd, take that to about 6k, then I hit 3rd and a second later the car loses all power and nose dives down. I let off and it drives normal again.
I'm sure it's fuel. But where. I can't imagine the pressure needs to go up. It’s at 7psi now. I have a 3/8s feed line and a 1/2" return line. Don't know if the difference in line size affects anything. There's also a vacuum port on the regulator that I believe increases pressure at WOT, it's capped off but not sure if that is worth looking into. I don't think the pump is running dry but I did only have a 1/4 tank of gas. Carb issues? PV not working?
Thanks for Looking!"
thats a classic symptom of the carbs fuel bowls running dry because the fuel supply is not consistent.
this is far more frequent with the dead head fuel pressure regulators OR when guys place the return style regulator before the carbs inlet port.
obviously your fuel filter(s) and fuel line internal size and fuel pump volume and pressure, have an effect your results
Id suggest at least temporarily connecting a fuel pressure gauge at the carbs fuel inlet port so you can monitor the fuel pressure at that point during a race.
if the pressure falls at the carbs inlet port its a supply issue, if its consistent I,d be looking at a blockage in the fuel inlet ,especially if its got a brass in carb filter.
you might be amazed at what a few tests with a fuel pressure gauge can tell you
IF YOUR CURRENT FUEL PUMPS CORRECTLY SET UP AND FUNCTIONING, you should not have any problem, but a partly clogged fuel filter might also be a problem.
the fuel pressure gauge at the carbs inlet port should let you know what to look for.
QUESTION
How do I adjust the fuel level on my carburetor?
ANSWER Setting the fuel level should be the first thing you do before attempting to make any further adjustments.The float level should put the fuel level just below the bottom of sight plug hole. You will make the adjustment with the vehicle on a level surface and the engine idling. You will first remove the sight plug, then to make your adjustment you will need to loosen the lock screw on the needle and seat. This will allow you to turn the adjusting nut to raise or lower the float level. Each hex flat on the nut will change the float level approximately 1/32". When you have the fuel level just below sight plug hole you will then tighten the lock screw and reinstall the sight hole plug. Make sure you have a shop towel handy in case you have any fuel leaks from the Sight plug or needle and seat adjusting nut.
first step is always to verify both fuel bowls have the floats correctly set (EASY ON MOST HOLLEY CARBS WITH A SITE PLUG)
these brass inlet filters need to be replaced occasionally as they tend to restrict fuel flow
RELATED THREADS
viewtopic.php?f=55&t=211
viewtopic.php?f=55&t=1939
viewtopic.php?f=55&t=635
viewtopic.php?f=55&t=109