I got my LM-2 wideband monitor working and have been playing around with the carb.
Heres the specs:
302
Edelbrock Performer RPM heads
RPM Air Gap intake
Crane Energizor 260 cam (204 at .050), .456 lift on both valves.
Pertronix Ignitor ignition at 12* with the advance plugged.
Gearing:
TKO600 (.64 OD)
2.79 rear end
60pm in 4th gear is about 2100rpm. 75 in 5th gear is 1700rpm.
Carb Spec:
Holley 600 vac secondaries
Primary Jets - 64
Power Valve is a 7.5
Stock Accelerator pump (30cc I believe) and discharge nozzles which say 0.031
Original Pink/redish accelerator pump cam.
Black Secondary Spring(heaviest)
Idle conditions
* Mixture screws were adjusted for highest amount of vacuum.
900 RPM
vacuum fluctuates slightly at 18-19 inches
AFR about 12.3
After reading about tuning with a wideband, I read that at idle the mixture should be about 14.0 When I adjust it to make it that, it starts idling rough, rpm drops to about 750-800, and vacuum drops and starts to become erratic around 15 inches or so. Is this normal? I dont really suspect that I have a vacuum leak because if I leave the idle mixture at 12.3, I can unscrew the idle speed set screw and it will idle smooth down to 600-700.
Cruise Conditions
40mph 2000rpm (3rd gear) and 1500rpm 4th gear, mixtures stays around 14.3 + / - .6 of a point. Also is about the same at 60mph in 4th(2000 rpm) and 75mph in OD(about 1700rpm)
Part throttle acceleration(just normal driving around town and going from 60-70mph on highway)
Any gear, any speed, AFR goes lean, 16-17 until I back off and hold a steady speed then it goes back to around 14.
Full throttle acceleration, from 2000 rpm, in any gear:
AFR goes lean, from 14's(cruise) to 16 even saw 17for about 3 or 4 seconds then goes back to 13, as rpm increases AFR keeps getting richer and by 4000-5000 rpms is in the high 11's and still getting richer.
During full throttle acceleration, when I get back on the gas pedal after I shift into second there is about a 2 second hesitation, AFR goes lean, 16.0 even seen 17 once, then a slight pop out of the exhaust then it starts pulling hard. I put a lighter(purple) spring on my secondaries to see if the problem worsened and it was about the same. Once everything caught up, the AFR was slightly richer with the lighter spring.
My concern is my accelerator pump circuit. Any advance on the throttle being even ever-so-slightly or full throttle then AFR goes lean 4 points for about 3 to 5 seconds then slowly starts to richen back up.
In neutral If I rev it the first few times it will slightly stutter but after a couple revs the stutter goes away.
How do I know if I should I mess with the accelerator pump cam or nozzle sizes? Looking down the carb and revving it it looks to me like a lot of fuel comes out very quickly. but not much if the throttle is moved slightly. I think ill put a real aggressive off-idle cam in there and see what happens.
What affect does a larger discharge nozzle have? it will give more fuel quicker vs a smaller nozzle which will spread the amount of fuel out over a longer time period?
Heres the specs:
302
Edelbrock Performer RPM heads
RPM Air Gap intake
Crane Energizor 260 cam (204 at .050), .456 lift on both valves.
Pertronix Ignitor ignition at 12* with the advance plugged.
Gearing:
TKO600 (.64 OD)
2.79 rear end
60pm in 4th gear is about 2100rpm. 75 in 5th gear is 1700rpm.
Carb Spec:
Holley 600 vac secondaries
Primary Jets - 64
Power Valve is a 7.5
Stock Accelerator pump (30cc I believe) and discharge nozzles which say 0.031
Original Pink/redish accelerator pump cam.
Black Secondary Spring(heaviest)
Idle conditions
* Mixture screws were adjusted for highest amount of vacuum.
900 RPM
vacuum fluctuates slightly at 18-19 inches
AFR about 12.3
After reading about tuning with a wideband, I read that at idle the mixture should be about 14.0 When I adjust it to make it that, it starts idling rough, rpm drops to about 750-800, and vacuum drops and starts to become erratic around 15 inches or so. Is this normal? I dont really suspect that I have a vacuum leak because if I leave the idle mixture at 12.3, I can unscrew the idle speed set screw and it will idle smooth down to 600-700.
Cruise Conditions
40mph 2000rpm (3rd gear) and 1500rpm 4th gear, mixtures stays around 14.3 + / - .6 of a point. Also is about the same at 60mph in 4th(2000 rpm) and 75mph in OD(about 1700rpm)
Part throttle acceleration(just normal driving around town and going from 60-70mph on highway)
Any gear, any speed, AFR goes lean, 16-17 until I back off and hold a steady speed then it goes back to around 14.
Full throttle acceleration, from 2000 rpm, in any gear:
AFR goes lean, from 14's(cruise) to 16 even saw 17for about 3 or 4 seconds then goes back to 13, as rpm increases AFR keeps getting richer and by 4000-5000 rpms is in the high 11's and still getting richer.
During full throttle acceleration, when I get back on the gas pedal after I shift into second there is about a 2 second hesitation, AFR goes lean, 16.0 even seen 17 once, then a slight pop out of the exhaust then it starts pulling hard. I put a lighter(purple) spring on my secondaries to see if the problem worsened and it was about the same. Once everything caught up, the AFR was slightly richer with the lighter spring.
My concern is my accelerator pump circuit. Any advance on the throttle being even ever-so-slightly or full throttle then AFR goes lean 4 points for about 3 to 5 seconds then slowly starts to richen back up.
In neutral If I rev it the first few times it will slightly stutter but after a couple revs the stutter goes away.
How do I know if I should I mess with the accelerator pump cam or nozzle sizes? Looking down the carb and revving it it looks to me like a lot of fuel comes out very quickly. but not much if the throttle is moved slightly. I think ill put a real aggressive off-idle cam in there and see what happens.
What affect does a larger discharge nozzle have? it will give more fuel quicker vs a smaller nozzle which will spread the amount of fuel out over a longer time period?
