I’m using an A/F ratio gauge to help me get my carb jetting dialed in. I’m lean at both idle and cruising, which I expected, since I have a hotter than stock cam, and more free flowing exhaust.
Quick question on idle circuit and main jets. Does the main jet affect the amount of fuel going to the idle jet, or are they separate circuits?
I’m wondering if increasing the size of the main jet would have a corresponding richening on the idle circuit, without increasing the idle jet, or if I need to increase the size of both main and idle jets.
Of course, if the main jet is already larger and flows more than the idle jet, then I wouldn’t think there would be any change at idle unless I changed that jet too.
Also, I have two sizes larger for the primary idle jet, but don’t have any larger ones for the secondary idle jet. Do I need to increase the size for both to affect idle, or only the primary? I could always drill out the secondary to make it larger….
For reference, A/F is 14.9-15.5 steady cruising in 4th at 2300 RPM, and 15.9-17 at idle. Brand new engine with 250 miles on the rebuild, engine fully heat soaked, and I’ve confirmed that there are no intake or exhaust leaks.
Current jets are :
Primary
Idle - 80 (drilled out to 0.85)
Main - 136
Secondary
Idle - 75
Main - 171
Quick question on idle circuit and main jets. Does the main jet affect the amount of fuel going to the idle jet, or are they separate circuits?
I’m wondering if increasing the size of the main jet would have a corresponding richening on the idle circuit, without increasing the idle jet, or if I need to increase the size of both main and idle jets.
Of course, if the main jet is already larger and flows more than the idle jet, then I wouldn’t think there would be any change at idle unless I changed that jet too.
Also, I have two sizes larger for the primary idle jet, but don’t have any larger ones for the secondary idle jet. Do I need to increase the size for both to affect idle, or only the primary? I could always drill out the secondary to make it larger….
For reference, A/F is 14.9-15.5 steady cruising in 4th at 2300 RPM, and 15.9-17 at idle. Brand new engine with 250 miles on the rebuild, engine fully heat soaked, and I’ve confirmed that there are no intake or exhaust leaks.
Current jets are :
Primary
Idle - 80 (drilled out to 0.85)
Main - 136
Secondary
Idle - 75
Main - 171
Last edited: