Weberology 101 Final Exam

[higgy]

http://mysite.verizon.net/vze2hw9t/

Its up including the WeberMod.doc

[Tamburinifan]

Nice work, thx f sharing!

[higgy]

Gert
You are most welcome, I'll be adding content as time goes by
I have a few other projects in the works as you are aware and I plan to share them all with everyone here who cares to look
Just my way of saying thanks to all of you here that have helped me along the way
higgy

[persempre907]

It's a great work.
When I had got the 906, I had ALL those problems (misfirings, flat spots, etc).
I'm happy that after 20 years there is the medicine.
Ciao

[paso750]

I really like what you guys made out of this.
I hope you don`t mind that I still have some questions/comments though.
- AFR: does an AFR increased by 0,5 mean the engine`s running leaner ?
- airbox mod: The quote is taken a bit from the context as it refers to the ST4 which has a similar airbox design like the SS/8xx/907ie but not P750/906. As correctly stated somewhere lower on the P750/906 it`s purely experimental at this point
- fuel pressure: I read a few posts in other forums lately saying that replacing the electric fuelpump with an underpressure fuelpump from a jap bike or newer Duc made a huge improvement for the Weber all over the revv band. Ever tried ?
- alternative aftermarket coils: also NOLOGY: ProFire PFC-30S (152 051 300), Andrews: CW140403
- "Warm air is better for burn mixture (helps with fuel atomization)" pls. explain. Cold air has a higher density, contains more oxygen and allows a greater cylinder filling so I don`t really understand this

Higgy, can I put it also in the downloads ? At least in my downloads thread. The download section of the site is still being worked on. At least Mike wanted to do some changes some time ago as there`s basically no webspace left to upload more stuff.

G.

[higgy]

I really like what you guys made out of this.
I hope you don`t mind that I still have some questions/comments though.

Thank You G and question are always welcome

AFR: does an AFR increased by 0,5 mean the engine`s running leaner

You got it. Any number below 14.7 is rich any number above 14.7 is lean. It represents the ratio of parts of air to parts of fuel so a larger AFR number means there is more air, therefore leaner mixture.

airbox mod: The quote is taken a bit from the context as it refers to the ST4 which has a similar airbox design like the SS/8xx/907ie but not P750/906. As correctly stated somewhere lower on the P750/906 it`s purely experimental at this point

Not sure I understand this one G

alternative aftermarket coils: also NOLOGY: ProFire PFC-30S (152 051 300), Andrews: CW140403

I'll be making some changes as time goes by,still not happy with a few parts here and there,I'll be sure to add these other options

Warm air is better for burn mixture (helps with fuel atomization)" pls. explain. Cold air has a higher density, contains more oxygen and allows a greater cylinder filling so I don`t really understand this

Vaporization of gasoline is a complicated subject. While it s is true cold air is denser. Fuel is a mixture of compounds each having their individual vaporization points. For ignition to occur
you need a minimum percentage of these compounds to be vaporized, Vaporized compounds burn and in turn provide the required heat to raise the rest to their vaporization point and a controlled chain reaction occurs. When they all reach their "flash points" together you get an explosion rather than a burn and spark knock is the result.. Cold air inhibits vaporization. These compounds do not burn in liquid form,they must be vapors. Also liquids tend to fall out of fast moving airflows especially at high pressures further complicating combustion. One other thing to note cold air leans the fuel mixture further...More air(cold air is denser) + same fuel = lean mixture and is harder to burn
Don't know if any of this helps

Higgy, can I put it also in the downloads

But of course, I had asked Jon about it but he has as yet not responded. Have not heard a peep out of Mike for months now.............SO i decided to put up a web page to make in available asap

[paso750]

Not sure I understand this one G

as discussed before after the P750/906 the airbox design was changed. The airfilter went from the back to the top as did the inlet snorkels. The cover and filter is slightly leaning forward. This is the kind of airbox that is tbeing talked about in the Desmoquattro Performance Handbook. You can cut open the airbox lid or only remove the snorkels and you`ll benefit from it. You can probably do that also with a 907ie but not with a P750 or 906 as the airbox design is a different one. Just cutting off the airbox top as suggested would put the airfilter out of function, too. (Thinking of it one could cut off the top, put an oval K&N directly on the Weber, remove the original airfilter and close the inlet snorkels). There`s no proof that copying any airbox mod that is done to a ST/SS/8xx etc has performance benefits also on a Paso. Therefore I wouldn`t recommend this. Everyone that reads about this and just hacks up the airbox does it on his own risk.

Vaporization of gasoline is a complicated subject. While it s is true cold air is denser. Fuel is a mixture of compounds each having their individual vaporization points. For ignition to occur
you need a minimum percentage of these compounds to be vaporized, Vaporized compounds burn and in turn provide the required heat to raise the rest to their vaporization point and a controlled chain reaction occurs. When they all reach their "flash points" together you get an explosion rather than a burn and spark knock is the result.. Cold air inhibits vaporization. These compounds do not burn in liquid form,they must be vapors. Also liquids tend to fall out of fast moving airflows especially at high pressures further complicating combustion. One other thing to note cold air leans the fuel mixture further...More air(cold air is denser) + same fuel = lean mixture and is harder to burn
Don't know if any of this helps

Of course with more air you need more fuel to keep a steady mixture. But somehow I can`t get these things together. Forever it was a performance aim to get as much clean and cold air to the engine as possible. If it was with a turbo or compressor giant intercoolers would be used to cool down the air. Naturally aspired engines would have the inlet snorkel of the airbox behind the front grill. NOS does nothing else than cool down the mixture so much that you`ll get the highest cylinder filling possible. Warm air was always known to be a perfomance killer.
I have to chew on this one for a bit.

G.

[higgy]

Yes intercoolers are used on turbo engines, but to cool it down from hundreds of degrees to maybe 75 degrees(23C) Once the charge gets below about 40F(4C) you start to have other issues

Just cutting off the airbox top as suggested would put the airfilter out of function, too.

I see the confusion now, I can correct it ..By top of the airbox Romus is refering to the cover which holds the filter in place not the "TOP"

I have removed about 2 inches from the top of my cover which exposes the top part of the filter and removed the snorkels as well
Language is always an issue

[romus]

- airbox mod: The quote is taken a bit from the context as it refers to the ST4 which has a similar airbox design like the SS/8xx/907ie but not P750/906. As correctly stated somewhere lower on the P750/906 it`s purely experimental at this point...

Yes, I agree, it is a bit out of context, so we will change it. I was trying to show why Paso owners have played with the airbox lid i.e. they have good reason.

But, we are not presenting an "airbox mod" only making a point that the Air Fuel Ratio (AFR) enriches by ~0.5 when the lid is opened somehow. That information can help in understanding jetting differences when tuning a carb.

The point is to understand that and settle on whatever you do to your airbox lid and air intake before tuning your carb. Or, to understand that if you make changes to your airbox lid, then you will likely need to rejet your carb slightly.

[paso750]

higgy, I guess my problem is that when reading "warm" I think "hot" which is definetely no good, so I probably just should ask myself how warm is "warm".

Renaming top to lid should make things clearer.

Warwick, I understand your intentions. Risk is always that someone takes something written for granted and goes for it without thinking that this is not an instruction but only a possibility that still requires some thoughts being put into it.
I generally agree that airbox mods can be a step into improving perfomance. I still disagree though (although I have no facts to prove this) that copying mods that are done to a ST/SS etc airbox have the same effect on a Paso. You may have a richer AFR w/o the airbox lid but I think (don`t know 4 sure) that the effect will change totally from mid speeds upwards due to the whole different design of the bike, fairing and airbox. I think AFR will then drop. Using open sport filters instead of an airbox sometimes leads to the same. (which of course depends on mounting position, angle etc of the filters)

G.

[romus]

...Renaming top to lid should make things clearer

.

Yes I agree. We'll update it.

I generally agree that airbox mods can be a step into improving perfomance. I still disagree though (although I have no facts to prove this) that copying mods that are done to a ST/SS etc airbox have the same effect on a Paso. You may have a richer AFR w/o the airbox lid but I think (don`t know 4 sure) that the effect will change totally from mid speeds upwards due to the whole different design of the bike, fairing and airbox. I think AFR will then drop. Using open sport filters instead of an airbox sometimes lead to the same. (which if course depeds on mounting position, angle etc of the filters)G.

Having a richer AFR when the airbox lid is opened to some degree seems to me to indicate that the carb is wanting more air if the effect is by more air that the venturi vacuum becomes stronger, thus pulling out more fuel into the venturi and down into the combustion chamber, thus richer by just a bit.

Ha, I tried to tape my homemade manometer inside the airbox in the hope of making a way to see the pressure effect just above the air horns when riding. Didn't work though - would need a more sensitive and costly measuring device - interesting though.

Ha, it's another subject, but I concluded that the holes in my airbox lid were were not such an overall guarantee of performance improvement and that if I could improve low end response in other ways I might be better off with it closed and with increased plenum air.

[paso750]

To my understanding an underpressure fuelpump shouldn`t enrich the AFR. Theoretically it should be the ideal as the fuel pressure depends on the current intake suction of the carb so fuel pressure varies depending on throttle position. This may positively influence ie low speed acceleration problems. What do you think?
Maybe I can still find that, it was in some german Duc forum ...

[higgy]

higgy, I guess my problem is that when reading "warm" I think "hot" which is definetely no good, so I probably just should ask myself how warm is "warm".

At the moment I have a 195 Cummins engine going for a baseline test.
Its a diesel but just as an example........
Our combustion air unit is suppyling air at 77.6 F
The turbo heats it up to 285 F
and the intercooler reduces back to 89
Pretty typical output of 197.3 HP and 414 lb ft of torque @ 2500rpm not too shabby

[higgy]

but I thought maybe one reason the increased 4.5 aux venturi mod improves low speed response is because the Paso airbox design is not the best for air resonation and so the taller venturi compensates. But, I don't really know that is why. I can be part of the reason.

The taller Aux Vent does two things
The first is it provides a stronger vacuum signal to the fuel reservoir. This improves the perculation in the ET and brings the main in sooner
The second is it reduces cross circuiting between the two sides of the carb by being taller than most standing waves which cause the cross circuiting a lot to do with the airbox characteristics. Opening the airbox helps as well.......

[higgy]

fuel pressure: I read a few posts in other forums lately saying that replacing the electric fuelpump with an underpressure fuelpump from a jap bike or newer Duc made a huge improvement for the Weber all over the revv band.

Fuel pressure needs to be consistant and enough of a supply to prevent fuel starvation. That is all that is required. The gross jet should help regardless of pressure by improving flow and response.
One other thing to note about the difference in return lines with the 906 as compared to the rest
A free flowing return line prevents vapor lock