AmickRacing
07-31-2011, 12:22 AM
This problem somewhat snuck up on us, I'll give you a brief run down of what went on...
I put a new Willy's carb on around a month ago, prior to that the car was running decent, but only had a couple nights on it this season. It's a steel headed WISSOTA motor belt drive fuel pump off of the front of the motor.
With the new carb on, it seemed to be kinda dead through and off of the corners, kind of blamed the carb, did some tweaking (per Willy's), it helped slightly, but still wasn't great. Paid more attention to the fuel system, noticed the pressure was low, like 2 lbs at idle, and 7 on the high end. Adjusted that a bit, helped some, but noticed that the fuel pressure was bouncing real bad down the straight's. Can't say that it was or wasn't doing that before, but it was noticeably worse.
Put the old carb back on, checked the filter, tank is clean (no pickup, just RR corner fitting), opened the holley regulator and it was clean. Still had the issue.
This week I paid more attention to the gauges, noticed and felt that in the corners it was bobbling really bad, very low pressure in the corners (bouncing between 0-2, then 1-4 on exit, then 6-9 down the straight). We swapped fuel regulators, put a different carb on, checked the filter again, changed fuel pumps. The other fuel pump had a crack where the fitting goes, so we had to re-swap them.
Anyway, main even, same story. Of course the more hooked up the track is the worse it is, but even in the slick I was struggling with it. And of course when the motor isn't putting out the power it should, the car goes to crap.
I'm leaning to believe it's a fuel line that's sucking shut. Today in the shop we ran a short line from the fuel pump into a fuel jug and ran it off that, when you rev it up to 5k, the fuel pressure will go up to around 8.5 or so, it's solid for a couple seconds then starts bouncing around about 2 lbs. I know the shop test isn't as good as the track, but gotta try something. Tried a different gauge too, same thing.
The fuel lines are kind of old, so replacing them wouldn't be all bad anyway.
I'm struggling to believe it'd be the fuel pump, there's really not much to the fuel pumps internally. I'm pretty sure there's no air leaks or cavitation going on... I'm kinda stumped. Any weird things to look for that you guys can think of?
I put a new Willy's carb on around a month ago, prior to that the car was running decent, but only had a couple nights on it this season. It's a steel headed WISSOTA motor belt drive fuel pump off of the front of the motor.
With the new carb on, it seemed to be kinda dead through and off of the corners, kind of blamed the carb, did some tweaking (per Willy's), it helped slightly, but still wasn't great. Paid more attention to the fuel system, noticed the pressure was low, like 2 lbs at idle, and 7 on the high end. Adjusted that a bit, helped some, but noticed that the fuel pressure was bouncing real bad down the straight's. Can't say that it was or wasn't doing that before, but it was noticeably worse.
Put the old carb back on, checked the filter, tank is clean (no pickup, just RR corner fitting), opened the holley regulator and it was clean. Still had the issue.
This week I paid more attention to the gauges, noticed and felt that in the corners it was bobbling really bad, very low pressure in the corners (bouncing between 0-2, then 1-4 on exit, then 6-9 down the straight). We swapped fuel regulators, put a different carb on, checked the filter again, changed fuel pumps. The other fuel pump had a crack where the fitting goes, so we had to re-swap them.
Anyway, main even, same story. Of course the more hooked up the track is the worse it is, but even in the slick I was struggling with it. And of course when the motor isn't putting out the power it should, the car goes to crap.
I'm leaning to believe it's a fuel line that's sucking shut. Today in the shop we ran a short line from the fuel pump into a fuel jug and ran it off that, when you rev it up to 5k, the fuel pressure will go up to around 8.5 or so, it's solid for a couple seconds then starts bouncing around about 2 lbs. I know the shop test isn't as good as the track, but gotta try something. Tried a different gauge too, same thing.
The fuel lines are kind of old, so replacing them wouldn't be all bad anyway.
I'm struggling to believe it'd be the fuel pump, there's really not much to the fuel pumps internally. I'm pretty sure there's no air leaks or cavitation going on... I'm kinda stumped. Any weird things to look for that you guys can think of?