Velocity Stack

[Duccout]

Well, the problem is that the air is full of dust, so you may as well just throw handfuls of sand into your engine!

[themoudie]

Aye 1039SOSH,

I have no idea where you live, so cannot pass comment on

just throw handfuls of sand into your engine!

from Duccout, except to say that I have run my '74 450 MKIII for over 75,000 miles, with no air filtration since 1976. However, this has been the damp and not so dusty UK and the engine required a new set of rings at ~55,000 miles and has had a rebore and new piston at just over 75,000 miles.

Are you aufait with the tuning of a DellOrto UB24 carb and the price of tuning parts?

Have you modified the engine and exhaust system to match the revised carburation?

How many miles are you intending to ride the bike?

If you still wish to add the velocity stack, have a good read of this: Dellorto_manual.pdf

View the contents and prices on this website: Eurocarb-Dellorto_website

Good health, Bill

[Jordan]

It broke my heart when I decided during the last big drought, to use a filter instead of the shiny "racer" accessory inlet cone.
They do have appeal, especially for a pretentious cafe type like me, but I live on a dirt road and the dust was too evident.
OK for folk in the UK, where it rains all the time and dust particles instantly turn into mud and tend to avoid being sucked in.

I knew someone with a Chater-Lea 350, sort of a Ducati single style lightweight bike of the 1920s, used for club road events.
He used an inlet cone with some nylon stocking material held on with a rubber band as a filter - best of both worlds!

There are different lengths available for the cones.
The best looking ones are long, but evidently short ones work better on some engines, such as my 450 Desmo had ex-factory.
So of course I fitted a long one, as every good cafe-racer should have.

[DesmoDog]

I ran one on my 160





BTW those were both taken before it was running, the clamp was installed before any gas was in the tank.

I'm not so sure about the substantial increase in air. If the porting is restrictive it doesn't matter how free flowing the intake is upstream of the carb. IIRC I didn't change anything on mine to run the stack. Maybe the needle position but I don't recall buying different jets.

The length is based on whatever RPM you want to boost the torque curve. The longer the stack the more time it takes for pressure waves to bounce back and forth, so a longer stack will "hit" at a lower rpm. Nothing's free though - while it helps at some rev ranges it hurts in others.

[Duccout]

It is funny, but all this stuff about gas flow.... Years ago, the best motorcycle mag of all time, Cycle, carried a series on tuning the Yamaha SR500 Single, and as a first step they borrowed famous tuner Jerry Branch's flow bench. After mucking about all day and getting wildly varying results whatever they did, mostly worse than the stock port, just for a laugh they stuck a stalagmite of clay in the middle of the port and got their best flow result, probably as a result of speeding the gas as it rushed past the obstruction. They also found that the valve guide did not obstruct flow at all.

It just makes me wonder how many hours I wasted in my youth attempting to improve gas flow, probably to no effect, although it made me feel better! It certainly is a black art. Has anyone seen the modern port tuning, where the surface is machined like the surface of a golf ball? The Germans even have a machine which will do it for you automatically! It wasn't like that in my day, all those hours spent polishing......

[DBDBrian]

Like most of us I expect, I have done my fair share of port polishing. Also I would think, like most, I had no access to a Dyno, so a blast up the road, quite likely indicated in your mind, the result you were looking for, but who knew at the time, what was really going on.
The 500 DBD Goldstar inlet port is 1- 7/16" at the mounting flange, using a 1-1/2" Carburettor, this set up during Dyno tests at the factory, was found to be the best arrangement, which would seem to contradict the general acceptance, of the need for a nice smooth port.

I am not suggesting for one moment that airbourne debris into the cylinder is a good idea, but having run motorcycles over the years with open bellmouth carburettors, (not off road) I can't say I have experienced any problems, other than the normal run of the mill.
As Jordan comments, a nice bellmouth, certainly looks the business. As too the how my 200 will perform, still remains to be seen.
With the age of the machines we are dealing with, I tend to think it's a matter of trial and error, to find the settings, which suits our personal requirements

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