Lidless Airbox - Posts from Roger are Welcome :)

[VTRDark]

Thanks for the correction, that's what I meant but got all confused and didn't word it right. I did try



(:-})

[thedeatons]

Thank you guys for the input. Hopefully this thread will help someone in the future

James

[8541Hawk]

'airpressure' within the airbox getting into the float bowl has nothing to do with 'pushing' fuel up to the jets..... air velocity going through the Carb body and over the jets sucks the fuel out, this is 'the Venturi effect'.

Well I can write out the whole vacuum theory thing again but I'm a lazy git so here is a link http://www.vtr1000.org/phpBB3/viewtopic ... 64#p315083

Basically, as counter intuitive as it sounds, vacuum does not pull anything. It is always the higher pressure pushing in that causes things to happen.
They best way I have come up with to illustrate what is happening is that Vacuum by definition is "nothing" (though we are dealing with "partial pressures" so there is still a bit of stuff left).

So we have a volume of "nothing" and we want to fill it with something, in our case a air\fuel mixture.
Moving the air\fuel mixture into our volume of "nothing" would be considered "work" by definition.

Which means if the vacuum "sucked" the air\fuel mixture into the volume, then the vacuum (or nothing as we defined it a bit ago) has just done work.
This is impossible as there is no such thing as free energy.

What is happening is the outside pressure is pushing in to fill the volume. Just like straight lines, nature hates a vacuum and will try to fill it anyway it can.

As I showed in the other thread, you have around 40 pounds of pressure pushing through the carb. This is where the energy to move the air\fuel mixture actually come from.

I can expand on these explanations if you would like as I have tried to keep it as simple as possible as I don't want to bore the hell out of everyone.

[mik_str]

There you go getting all technical on us again....

[bigtwinthing]

Are we talking 5bhp rise if your lucky? it does seem a lot of work for that, i do know you guys love to fix,fiddle and make them go better but iam totally bloody confused!!!!

[magnum]

Are we talking 5bhp rise if your lucky? it does seem a lot of work for that, i do know you guys love to fix,fiddle and make them go better but iam totally bloody confused!!!!

me to.

[8541Hawk]

There you go getting all technical on us again....

Only because I'm trying to help these guys understand what is really happening inside a vacuum operated carb.
Which is the first step in getting them really dialed in.

[YETI]

My airbox has had the top modification
and it works GREAT !! the reason for that
is because roger built it
ie : stage 1 with all the trimmings .
And cyberman , I should copyright
my pictures

YETI ..

[mik_str]

My airbox has had the top modification
and it works GREAT !! the reason for that
is because roger built it
ie : stage 1 with all the trimmings .

sadly, we here in the New World don't have that luxury......... though, thankfully, he is as helpful as any human can possibly be on e-mail.......

[VTRDark]

Only because I'm trying to help these guys understand what is really happening inside a vacuum operated carb.

Thanks Mike much appreciated.

So I was more or less right in the first place then. LOL atmospheric pressure pushes the fuel through the jets as the pressure differential is created. With the presence of lower pressure the higher atmospheric pressure pushes down to fill the void. Got it!

I know you have repeated stuff but your words are not wasted and it's slowly sinking in. Your drilling it into us well me anyway.

And cyberman , I should copyright
my pictures

Indeed you should FYI Unfortunately copyrighting pictures and putting them online does not guarantee someone not using/plagiarising them. Personally...most of the time I would respect a copyrighted image. Or... at least alter it beyond recognition of being the same.

I do apologise I should have really referenced the pics to you and or your bike. It was a bit of a brain bashing post that one.

(:-})

[mik_str]

Just thought of something (as we OCMD types are so apt to do) related to the crafted airbox lid I fashioned (see below)......



While, as per Roger, it is possible to sort out the fueling to get good power and response at all engine speeds, I was wondering about the possibility of adding a "gate" of sorts at the open end of the air diffuser in above pic. One could then use a small stepper motor, working though a likage, to have it open above, say half-throttle. THis would (theoretically) give you better intake velocity at low throttle opening (by limiting the filter area) for better power at low speeds while giving max flow at high speed when the engine can use more air..... I am nil in electronics, but I imagine it couldn't be that hard to split the wire coming off the TPS to get a reading (ie. throttle opening) and have some means to it activating the stepper motor once half-throttle is reached. Aleternatively, some form of reverse polarity switch could be mounted ont eh throttle linkage to get the same result.

Your thoughts gents? Be polite now, lol

[VTRDark]

Sounds like a positive direction to me though the involvement of motors connected to the throttle might be overcomplicating things. What your talking about sounds like a TPI valve. Now look what kind of sites you have me looking at
http://www.snowwest.ca/tpi/valve.htm

I did come across a site or forum somewhere, where a hole was cut out the side of the airbox. This then had a plastic pivoted door that could manually be opened or closed. IIRC the user made it so they could adjust the airflow according to climate conditions. I guess this was the poor man's version of a TPI valve. I wonder how closely related a flow commander is to something like this Ideally we need fine tuning control of fuel and fine tuning control of air. That would be the perfect mix.

I feel like we're going back in time here. Next we will be trying to work out how to put an advance and retard lever on the bars. LOL

(:-})

[mik_str]

TPI valves are used in snowmobiles. However, dust is not an issue when riding a sled, so they can get away with it..... My scheme may never amount to anything... but then again, it depends how long winter hands around, lol. Of course, a switch could be set-up on the throttle tube too, many possible ways to activate the gate via throttle movement, but the end result would be the ame, a variable venturi of sorts.......

[VTRDark]

Like I say it sounds like a positive direction. My brain hurts now, starting to get a headache starring at this screen. Got to get some sleep know.

(:-})