10-18-2017, 07:20 AM
(This post was last modified: 10-18-2017, 12:37 PM by doug tenney.)
Hi Mel,
Steve O is definitely the authority on kart carburetors.
However, I just want to make sure your original questions were answered...
Q. can you check the pop off on a assembled tilly carb attached to motor?
A. Yes. No need to take it apart.
Q. Also if you can check it on the motor is it the same reading as a disassembled one?
A. Same, but the readings will not be as crisp after the first "pop" or two, once air enters. Just don't blink when you pump it up the first time.
ALSO, I think I figured out EC Birt's balloon comment (referring to the link Duke provided):
I never thought about it before, but when you test "pop-off" through the fuel inlet fitting, the pump diaphragm (aka, skin) also has to withstand that pressure, which it never sees when the engine is running. I've never had one rip as a result, but I'm told that serious racers using Tillotson carbs buy the extra-thin pump skins and replace them every race day because they get a "belly" in them (i.e., they stretch a bit). As long as we're still talking carburetors, I'm not sure why a slight belly is bad... at very high speeds, it must affect the skin's response to the pressure pulses.
But I'm still confused by E.C.'s instruction to remove the HS needle...
Doug
Steve O is definitely the authority on kart carburetors.
However, I just want to make sure your original questions were answered...
Q. can you check the pop off on a assembled tilly carb attached to motor?
A. Yes. No need to take it apart.
Q. Also if you can check it on the motor is it the same reading as a disassembled one?
A. Same, but the readings will not be as crisp after the first "pop" or two, once air enters. Just don't blink when you pump it up the first time.
ALSO, I think I figured out EC Birt's balloon comment (referring to the link Duke provided):
I never thought about it before, but when you test "pop-off" through the fuel inlet fitting, the pump diaphragm (aka, skin) also has to withstand that pressure, which it never sees when the engine is running. I've never had one rip as a result, but I'm told that serious racers using Tillotson carbs buy the extra-thin pump skins and replace them every race day because they get a "belly" in them (i.e., they stretch a bit). As long as we're still talking carburetors, I'm not sure why a slight belly is bad... at very high speeds, it must affect the skin's response to the pressure pulses.
But I'm still confused by E.C.'s instruction to remove the HS needle...
Doug