Topic: Intake / Air filter question

[bmarshall]

I see a lot of people running filter pods on their carbs. Most of my vintage bike experience has been with 2 strokes and in that world filterpods are a big no-no. The flat backside causes a resonance and rich spot in the mid-range. my RD400 twin has a large single filter with 2 runners coming from it (y-boot). That way when one carb is blowing back the other is sucking in and no more rich spot. (On a 2 stroke the rich mid range spot is caused by the air bouncing backward through the carb, off the back of the filter pod and then back through the carb, passing through the carb 3x's).

What is the hot set up for a 550?

[Ecosse]

mr. 550 himself, two tired, has to my recollection urged against pods, in favor of stock air boxes, only to often fall upon deaf ears. this i believe for anything but all out engines.

i remember when moroso began offering air cleaners (for car) with the base contoured to promote air flow. but your post has me wondering about the effectiveness of an open element air filter functioning for pairs or all four carbs. dunno if it would address the phenomenon you cited.

[Ecosse]

below is a moroso cross section.

[lordmoonpie]

What is the hot set up for a 550?

Guess it depends what you mean by hot setup - would you not just use velocity stacks?

[Old Scrambler]

In a perfect 4-stroke world..........the valves are closed to the carbs on compression and exhaust.........hence no blowback.  In extreme cases of advanced timing and overlapped valve timing on a wild cam-grind, you may have a small amount of blowback opportunity.  Full airbox on the street is best.  Velocity stacks on the race track.  Pods are for show or street racing.  They are very difficult to tune for midrange at constant speed.

[voxonda]

For OEM carb's just use the OEM rubber stacks, do their job very good.

Rob

[bmarshall]

Lordmoonpie: On a RD350/400 the 'hot' set up is a combination of filter, intake manifolds, manifold crossover tube, and jetting that works on most all variations. I was curious if on a 550 there was a certain combination that worked fairly well and universal on a mostly stock bike (jetting, exhaust, filter et...) I had not thought about running v stacks. Aren't they generally run without filters?

Old Scrambler: would not the closed valve act like a 2 stroke piston when it comes up toward TDC and closes off the intake?

Not looking to start arguments, just looking to gather information and discuss theory (and experiences).

[Old Scrambler]

I generally stay away from 2-strokes.  As I understand it..........in a piston-port design, its the piston movement from the bottom toward TDC when the piston venturi is putting back-pressure on the carb.  I don't think that happens in a rotary-valve design........but I am not the expert. 

Most (all) 4-stroke racers with open stacks will use soft-balls or covers of some sort to block-off the stacks when the motor is not running. Several v-stacks have mesh-screens to keep large objects from entering the venturi. I have seen several of those designs with added foam for street use. You just have to replace the foam before it crumbles and gets sucked into the motor.  I use that type of filter on my 650cc single as do most modern off-road or dual-sport riders.

[bert96]

 Velocity stack are not easy to find at least for my carbs,i have carbs from a nighthawk cb700 '84.

Anyone know where i could find something that fit at a good price


Sorry to hyjack but i could not resist to ask the question

Bert

[MRieck]

below is a moroso cross section.

I like the way they show the air "bending" like it is par boiled pasta. Air with velocity to it doesn't bend....it wants to go straight.