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How would you describe the relationship between needle valve sizes and pop off springs? Talking about a Mikuni Super BN carb. For example:
You lower pop off by changing the arm spring from one strength to another (80 gram to 65 gram for example)... Would this be offset by lowering the size of the needle valve, too? Or to put it another way. Spring goes from 95 gram to 80 gram (20 psi to 17 psi per the charts available), but then you change the needle valve from 2.3 to 2.0 (17 psi back up to 21 psi per the Mikuni charts). How would the fuel regulator system be working differently if the end result is roughly the same psi?
Basically, how does the needle valve and pop off spring work in conjunction with each other?
I am working to reduce or eliminate a bog off of idle up to about 1/3 throttle. I've checked all the other usual culprits for bogs (air leaks, water leaks, electrical, etc.) Because I have a low hour stock motor, never touched until a wet pipe and Prok's were put on, that I feel it is the jetting that needs to be tweaked before blaming anything else. The high speed and low speed jets (i.e. main and pilot) were changed by a shop per Mikuni's jetting cheat sheet, but not pop off/NS. I'm not going to fool with the 3 water screws on the wet pipe until I address the pop off/NS settings. I feel the high flow exhuast and low restriction Proks are making the pop off arm stay closed to manifold pressure until that pressure overcomes the stock settings. I'm sure it doesn't help that I'm at 4800' elevation where I ride. So I'm going to adjust pop off (per Mikuni, this forum's posts, using Mikuni pop off gauges, plug readings and motor speed in water), but I'm foggy on the relationship of NS valve to arm spring strengths. Any advice?
How would you describe the relationship between needle valve sizes and pop off springs? Talking about a Mikuni Super BN carb. For example:
You lower pop off by changing the arm spring from one strength to another (80 gram to 65 gram for example)... Would this be offset by lowering the size of the needle valve, too? Or to put it another way. Spring goes from 95 gram to 80 gram (20 psi to 17 psi per the charts available), but then you change the needle valve from 2.3 to 2.0 (17 psi back up to 21 psi per the Mikuni charts). How would the fuel regulator system be working differently if the end result is roughly the same psi?
Basically, how does the needle valve and pop off spring work in conjunction with each other?
I am working to reduce or eliminate a bog off of idle up to about 1/3 throttle. I've checked all the other usual culprits for bogs (air leaks, water leaks, electrical, etc.) Because I have a low hour stock motor, never touched until a wet pipe and Prok's were put on, that I feel it is the jetting that needs to be tweaked before blaming anything else. The high speed and low speed jets (i.e. main and pilot) were changed by a shop per Mikuni's jetting cheat sheet, but not pop off/NS. I'm not going to fool with the 3 water screws on the wet pipe until I address the pop off/NS settings. I feel the high flow exhuast and low restriction Proks are making the pop off arm stay closed to manifold pressure until that pressure overcomes the stock settings. I'm sure it doesn't help that I'm at 4800' elevation where I ride. So I'm going to adjust pop off (per Mikuni, this forum's posts, using Mikuni pop off gauges, plug readings and motor speed in water), but I'm foggy on the relationship of NS valve to arm spring strengths. Any advice?
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