Looking for more pep off the line
With a Holley 4150/60.
First. Always check fuel level in both bowls before getting into the tune.
Most have sight plugs on the bowl. Traditional sight plugs are located so the fuel level should be just at the bottom of the plug (primary) and a little lower on the secondary bowl. New big clear window plugs aer usually set near the middle.
With carb off the engine check the primary transfer slot exposure under the throttle plates at idle are in the range of .020 - .040"
If it gets out of range, then there will be a delay or bog while driving or accelerating as the throttle opens. explanation here
You can check with feeler gage or drill bits.
The drill bit is next to the transfer slot.
The hole is the idle port.
Write down how many 1/4 turns in of the idle speed screw from just touching gets .020, 030, and .040.
Then you'll always know how far open the throttles are without removing the carb from the intake.
____________________________________________________________________________________________________________
Tuning for Performance.
This requires systematic trial and error to improve performance. Performance defined as power, torque and engine efficiency.
To do this, work with steady state conditions first.
Compare power and engine efficiency with something other than seat of pants.
Start at the idle and work up.
Idle and off idle are your foundations. If its crappy at idle then the engine is going to have to clear up before it can respond to additional throttle.
Performance here is going to be demonstrated by running fairly clean exhaust output and how little throttle is needed
(manual) to get into first gear without stalling.
(automatic) lose the least rpm when placed in drive.
Alternatively have the best vacuum at a given rpm in drive.
Work with initial timing, idle speed screw (transfer slots), and idle mixture screws.
Next confirm off-idle has good performance by very slowly accelerating from stop with no hesitation.
This test minimizes the role of the pump shot and focus on the idle circuit's begining of transition.
If that's good, then test more normal acceleration (for public streets) from stop to make sure the pump shot is not too much or too little for this basic job.
Then you can test out steady driving at various speeds. The fuel ratio at steady interstate highway speeds is determined by main jet and its air bleeds. Local highways is partial or completely idle circuit (transition slot, idle feed restriction and idle aiir bleed). So when possible drive steady interstate speeds to tune the main jets.
If jetting too lean, it will surge. Slow down and take it back to garage. Increase primary jets.
If you have access to the strip or dyno you can test wide open throttle in 3 or 4th gear. AFR at wide open throttle is controlled by the jets plus power valve channel restrictions. Change jets for the best mph through the lights.
If primary jetting for best power is different than jetting for best interstate highway mpg, adjust the power valve restrictions.
All the above tests are effected by timing. If you change timing at a given rpm and condition, then retest before change fuel mixture for that condition.
Once all that is tuned, then concentrate on transition conditions. They are:
opening the throttle quickly from low rpm (pump shot).
power valve opening point.
Reality is you may have to go out of sequence. You will almost certainly have to make repeats. How many repeats depends on how much interest and persistance you have.
Good luck!
With a Holley 4150/60.
First. Always check fuel level in both bowls before getting into the tune.
Most have sight plugs on the bowl. Traditional sight plugs are located so the fuel level should be just at the bottom of the plug (primary) and a little lower on the secondary bowl. New big clear window plugs aer usually set near the middle.
With carb off the engine check the primary transfer slot exposure under the throttle plates at idle are in the range of .020 - .040"
If it gets out of range, then there will be a delay or bog while driving or accelerating as the throttle opens. explanation here
You can check with feeler gage or drill bits.
The drill bit is next to the transfer slot.
The hole is the idle port.
Write down how many 1/4 turns in of the idle speed screw from just touching gets .020, 030, and .040.
Then you'll always know how far open the throttles are without removing the carb from the intake.
____________________________________________________________________________________________________________
Tuning for Performance.
This requires systematic trial and error to improve performance. Performance defined as power, torque and engine efficiency.
To do this, work with steady state conditions first.
Compare power and engine efficiency with something other than seat of pants.
Start at the idle and work up.
Idle and off idle are your foundations. If its crappy at idle then the engine is going to have to clear up before it can respond to additional throttle.
Performance here is going to be demonstrated by running fairly clean exhaust output and how little throttle is needed
(manual) to get into first gear without stalling.
(automatic) lose the least rpm when placed in drive.
Alternatively have the best vacuum at a given rpm in drive.
Work with initial timing, idle speed screw (transfer slots), and idle mixture screws.
Next confirm off-idle has good performance by very slowly accelerating from stop with no hesitation.
This test minimizes the role of the pump shot and focus on the idle circuit's begining of transition.
If that's good, then test more normal acceleration (for public streets) from stop to make sure the pump shot is not too much or too little for this basic job.
Then you can test out steady driving at various speeds. The fuel ratio at steady interstate highway speeds is determined by main jet and its air bleeds. Local highways is partial or completely idle circuit (transition slot, idle feed restriction and idle aiir bleed). So when possible drive steady interstate speeds to tune the main jets.
If jetting too lean, it will surge. Slow down and take it back to garage. Increase primary jets.
If you have access to the strip or dyno you can test wide open throttle in 3 or 4th gear. AFR at wide open throttle is controlled by the jets plus power valve channel restrictions. Change jets for the best mph through the lights.
If primary jetting for best power is different than jetting for best interstate highway mpg, adjust the power valve restrictions.
All the above tests are effected by timing. If you change timing at a given rpm and condition, then retest before change fuel mixture for that condition.
Once all that is tuned, then concentrate on transition conditions. They are:
opening the throttle quickly from low rpm (pump shot).
power valve opening point.
Reality is you may have to go out of sequence. You will almost certainly have to make repeats. How many repeats depends on how much interest and persistance you have.
Good luck!
