I have an '85 Mustang with a 306c.i. / 10.5:1 comp. / Custom Hydraulic Roller Cam @50-230dur,533lift / Victor Jr. / Demon 650 Race / MSD billet distributor with MSD 6AL ignition & blaster 2 coil.
The carb came with 71 primary/71 secondary jets and upon driving the car, it hesitated beyond belief and ran extremely lean. After going up in various jet sizes for the best fuel delivery, I ended going up 20 sizes to 90/91. With these jets, the secondaries run fine without hesitation, however, at off idle speed and low rpm's up to approx 3,500rpm, the car still hesitates and blubbers. After driving it for 60plus miles and checking the plugs, they're still white as can be.
I contacted the Demon tech's, and they told me that the 650 is plenty of carb for my setup and said that I may have a fuel delivery/volume problem. They recommended testing my fuel pump delivery by disconnecting my fuel line and placing it into a 1gal. can and timing how long it took the pump to fill the container. They said that it should take 24 seconds or less.
When I did this with my Holley Blue (110gph), it took close to a minute. When I told them that it took well over 24 seconds, they told me I wasn't delivering enough volume to the carb and they recommended their 220 HR which delivers 220gph. The tech stated that with this pump, my carb will get enough fuel, and that I will more than likely have to down size my jets.
After thinking about this, I though about the stock alternator (74amp) and wondered wether I was delivering enough amps to the pump. Regardless, with all described above, is it possible that my carb may be starved for fuel even when the bowls appear to be constantly full while running 7lbs of pressure through the regulator and with the larger jets? Also, as I mentioned earlier, the car doesn't seem to be starved when I throttle it and get up in the rpm's, only off idle and at a constant rpm below 3500.
Any input/suggestions extremely welcomed.
Thanks
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The carb came with 71 primary/71 secondary jets and upon driving the car, it hesitated beyond belief and ran extremely lean. After going up in various jet sizes for the best fuel delivery, I ended going up 20 sizes to 90/91. With these jets, the secondaries run fine without hesitation, however, at off idle speed and low rpm's up to approx 3,500rpm, the car still hesitates and blubbers. After driving it for 60plus miles and checking the plugs, they're still white as can be.
I contacted the Demon tech's, and they told me that the 650 is plenty of carb for my setup and said that I may have a fuel delivery/volume problem. They recommended testing my fuel pump delivery by disconnecting my fuel line and placing it into a 1gal. can and timing how long it took the pump to fill the container. They said that it should take 24 seconds or less.
When I did this with my Holley Blue (110gph), it took close to a minute. When I told them that it took well over 24 seconds, they told me I wasn't delivering enough volume to the carb and they recommended their 220 HR which delivers 220gph. The tech stated that with this pump, my carb will get enough fuel, and that I will more than likely have to down size my jets.
After thinking about this, I though about the stock alternator (74amp) and wondered wether I was delivering enough amps to the pump. Regardless, with all described above, is it possible that my carb may be starved for fuel even when the bowls appear to be constantly full while running 7lbs of pressure through the regulator and with the larger jets? Also, as I mentioned earlier, the car doesn't seem to be starved when I throttle it and get up in the rpm's, only off idle and at a constant rpm below 3500.
Any input/suggestions extremely welcomed.
Thanks
