Quote:
Originally Posted by Burdekin
Modified a SU6 stub stack for the Stromberg and added a K&N filter. Also made a new bottom bush for the rear shock.
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Been doing a bit of driving and it felt a bit down on acceleration so I got my other spare air filter housing and put in my old air filter and did a couple of comparison runs. Well it definitely is down on acceleration and maybe as much as 10mph along the road up from our cottage. I’ve been doing some reading and there are two possible reasons that I can think of. One website I found used a program to do some modelling of SUs with and without stub stacks and what they deduced was the height of the piston isn’t purely down to pressure difference through the carb but there is also a low pressure at the entrance of the carb due to the sharp change in direction which contributes to lifting of the carb. When you add a stub stack that low pressure is no longer there so even with increased air flow through the carb it still doesn’t lift the piston as much as standard.
I think there are two possible reasons that I can think of why the power is down, as described above or the increased air flow is resulting in a leaner mixture. I don’t have my wide band sensor setup so I don’t know exactly what is happening. At the moment I am not going to mess about with changing needles but if the low pressure scenario is correct then changing over the piston spring to a lighter spring may be a fix and I’m going to give it a try. If it doesn’t make things better then I will run the standard filter for now.