650gts
XS650 Enthusiast
Engine and carbs are in. I’m going with K&N style air filters. I’m guessing the two larger hoses coming off the engine are air hoses to the original air boxes? Do I just remove them and cap off the ports?
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Bobber build - air hose question
- Thread starter 650gts
- Start date
No, they are engine breather hoses, so you don't want to cap them. What many of us do is add one-way check valves to the hose ends. These let crankcase pressure out but don't allow any air to be sucked back in. This can produce a little bit of a vacuum in the cases, and that's beneficial for a couple reasons. First, it's said the motor can produce a bit more power like this and second, it can prevent oil leaks.
If you poise the ends of the hoses over your pods, any oil or oil mist that might come out will just be recycled through the motor .....
For a check valve, you don't want a PCV valve. They have a ball bearing inside and it can't respond quick enough to the engine's vacuum pulses. Instead, we use power brake check valves, available at most auto parts stores for about $5 each .....
The inlet end is a perfect fit into the stock breather hose.
Now a word about the pod filters you're considering. K&N style pleated pods don't work well with our CV carbs. They cause a turbulent air flow and that messes with the slide lift. Instead, get UNI straight foam pods as pictured above. For your BS38s, you will want UNI part #UP4200 or UP4200ST (dual layer).
If you poise the ends of the hoses over your pods, any oil or oil mist that might come out will just be recycled through the motor .....
For a check valve, you don't want a PCV valve. They have a ball bearing inside and it can't respond quick enough to the engine's vacuum pulses. Instead, we use power brake check valves, available at most auto parts stores for about $5 each .....
The inlet end is a perfect fit into the stock breather hose.
Now a word about the pod filters you're considering. K&N style pleated pods don't work well with our CV carbs. They cause a turbulent air flow and that messes with the slide lift. Instead, get UNI straight foam pods as pictured above. For your BS38s, you will want UNI part #UP4200 or UP4200ST (dual layer).
What 5twins said.
I used one of these on my last build. With a little filter off the end.
https://www.amazon.com/gp/product/B07KLPJBQ6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I used one of these on my last build. With a little filter off the end.
https://www.amazon.com/gp/product/B07KLPJBQ6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
