So I thought A velocity tube was all "relative"

[Blasterdude27]

Last summer when I switched to a pod I ran a velocity tube because I was always told to do so, so blindingly I did.

Well I had a clamp on for a 34mm carb so I had to run an adaptor and the tube... which ended up being very long. Needless to say I had clearance issues and it was always falling off mid ride and I was sick of dealing with it.

So recently I bought a new filter ( the right size ) and just slapped it straight off the carb. Fired it up and guess what? It ran horrible!!!
The thought that it was the filter didn't register with me, I just couldn't see how a velocity tube could make that much of a difference...... I ended up trouble-shooting like a mad man, check EVERYTHING, floats, dropped my jetting, upped my jetting (even though my jetting was spot on ), most of the electrical system, reeds, checked for air leaks... even pulled off my top end it see if I melted a ring ( even though my comps still good ) All to no avail...

So I was sitting there thinking what haven’t I done, checked the cdi, changed the head gasket, or pulled off the flywheel.
Well I thought if the cdi was bad... it wouldn't run... head gasket was new and if it was bad I would have a major air leak... if the stator was bad there would be no spark ( i had a mojave with a bad stator once... took me months to figure out what it was ) and if it was the keyway it would run backwards or fire wrong.
So then after all that it kinda clicked lol
I put on a new velocity tube and presto! Bike runs perfect again!

So people run those tubes! even if its something small... it will make a difference.

 

[Luni]

Im running a pod filter on my 36mm PWK carb, no velocity tube and my bike runs perfect.

 

[Blasterdude27]

My bike ran good right of idel to about 1/2 throttle, after that it fell off and bogged down.... I tried changing my jetting around but nothing changed it.
I can't explain it lol all I can say is velocity tubes work.

 

[Luni]

Velocity tube, has a funnel style tapered inlet under where the air filter goes righ? Like a velocity stack on a normal car ya?

I know they work on cars, Im sure they work on these good too.

 

[Blasterdude27]

Velocity tube, has a funnel style tapered inlet under where the air filter goes righ? Like a velocity stack on a normal car ya?

I know they work on cars, Im sure they work on these good too.

No its just a 3-4" tube you run in-between your carb and clamp on...

Your thinking of a velocity stack...

 

[Luni]

Hmm. I wonder if a velocity stack would do anything for us.

 

[phragle]

and you guys didn't believe me......

 

[Little-J]

Depending on your porting, the inertia of the air traveling down the tube can make a big difference in performance to an off road style two stroke. thats why the original blaster and ALL twostroke dirt bikes have the massive tube half way to the back of the bike.. Otherwise, if short was better, we'd have intakes where Husaberg puts it on their 650 thumper (the gas tank has a big hole in the middle for the air filter)..

Not to be confused with the resonance of the stack.. This is well too low for the engines on our blasters and thats why people have boost bottles, because the resonance of the intake velocity stack is C**P.. sorry.. I felt passionate about using that word!

 

[EToX]

I'm not certain this would apply here but I know that on 4-strokes a longer velocity stack will help low end while a shorter one will help top end.

Note: length is relative to inlet/venturi diameter, I.E. I run a Dell'orto 48 DHLA on my Rx-7 with 52 mm V-stacks for all out hi-way speed, venturi diameter is 46mm. To pick up some good low end I will swap up to as much as 86mm stacks. Distance between the inside of your filter and the inlet on your stack is important too, general rule of thumb is 50mm.

Hope this helps!

 

[homdaddy]

blasterdude can we get a picture of your setup.im about to get my 245 going and need to see, but im running a 38 pwk