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Old 07-24-2013, 10:42 PM   #1
Head2Wind OP
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Thoughts and musings of a serial tuner

The other day, while having a phone conversation with the owner of Factory Pro (Marc Salvisberg) about some of his new ideas he shared one of his previous discoveries with another motorcycle that was extremely sensitive to cross winds. Based upon his research and development of that motorcycle at the time he came to the conclusion "fuel bowl vent pressure must equal post airfilter pressure".

Now, this has been discussed briefly in relation to the LC8 and isn't necessarily a "blink, NEW IDEA moment", but I don't think that it really got much development time with the LC8. For me I was being lazy because I "had a solution that I knew worked".

Not that I have a bunch of spare time to really fully work this to its end I decided to at least satisfy some of my curiosity. The challenge is how to accomplish the requirements while being able to maintain a clear path for venting. In other words this means that running hoses down from the carbs through the bottom of the airbox and then back up to the top of the airbox (clean side of the air filter) would not work reliably because any liquid fuel could pool at a low point of the hose and block air flow. The solution I first tried was to rotate the bowl vents up and punch holes through the pink foam area to gain access to the "post air filter pressure". This will probably work, but I didn't like the way the filter both needs to be modified but also it distorts slightly. There are other factors too, like if liquid fuel comes out of the vents then it will definitely soak the filter.










Soooooo...... I have a new better idea that will not require cutting the filter but will require putting some hose fittings in a couple spots. More to come as soon as I can find the time to cut/paste/connect. Then the fun begins in real time, someone gets to finger out the proper jetting to make it all work
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Old 07-24-2013, 11:45 PM   #2
rusty43
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Question

hmmmm, and your h2w/unifilter/flexjet kit is on its way to me as we speak. will you still have to use different length vent tubes or could you tee them under the carbs and just send one tube up to the top via a couple of 90* fittings?

and you'll have near atmospheric pressure at idle and less than that at WOT. does that mean larger mains are required?
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Old 07-25-2013, 07:31 AM   #3
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Regarding the question of what jet sizes it will require are yet to be determined. I have a very rough idea, however I could be very wrong.

I'm not going to have any spare time to do much with this idea so I figured I'd share it and someone else could give it a go.

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Old 07-25-2013, 08:04 AM   #4
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Shouldn't make a difference as long as the filter is clean, or am I missing something?
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Old 07-25-2013, 08:53 AM   #5
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Why are you doing this?

Also this would put a 'U' in the vent lines won't it - they won't drain and may block with liquid??

Pressure difference across the filter will be very small until at high airflows i.e. ~full load very high speed 7000rpm + so it will only make a difference in that area....

I'm probably missing something here?
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Old 07-25-2013, 04:36 PM   #6
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Originally Posted by men8ifr View Post
Why are you doing this?

Also this would put a 'U' in the vent lines won't it - they won't drain and may block with liquid??

Pressure difference across the filter will be very small until at high airflows i.e. ~full load very high speed 7000rpm + so it will only make a difference in that area....

I'm probably missing something here?
Several reasons of "why"

1. Increase filter/s service interval prior to significant change in the quality of how the engine runs. As the filter/s become dirty the restriction of flow through to the clean side of the filter/s will increase. In turn, this will increase the pressure differential between the outside and inside of the air box, the standard bowls are "vented" to the outside. This will then cause the fuel delivery to change (go rich). On average, the absolute pressure will be lower inside the airbox on the clean side of the filter than the absolute pressure of the air near the bowl vent (in a standard configuration).
2. Eliminate transient pressure differentials between the intake tract and the fuel bowl. We feel it when actively riding in cross winds and other pressure transients manifested as "surging" or a "sag in power".

As far as the "U" question, I effectively eliminated the hoses by rotating the nipples up. Any liquid fuel that is present here would flow back down into the float bowl. Since I really don't like the results of doing this (it distorts the filter and a few other things that I mentioned), I am going to create a hose connection at the black bell adapters, right above where the airjets are located. This should get me dead clean air to vent the bowls to. Any liquid fuel will flow back into the bowls or into the throat of the carb.
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Old 07-25-2013, 04:42 PM   #7
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Originally Posted by Sporting Wood View Post
Shouldn't make a difference as long as the filter is clean, or am I missing something?

I am chasing the cross wind nasties and other oddities that happen at speed. I fingered it was worth a try. It gets even worse when trying to get the best MPG out of the open filter setup. When the fueling is nice and crisp for best MPG, the engine tends to hunt or surge with the slightest change in wind. If I can eliminate or significantly reduce the root cause of this problem, then it should be easier to tune for power AND best cruise MPG. Otherwise I find that I have to put more fuel to it to get it to behave, but then MPG goes into the shitter.
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Old 07-31-2013, 09:04 PM   #8
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My latest thoughts related to this subject. The really nice thing about this setup is that it will fit any of the filters and airboxes out there.

Now I just need to test and tune to make it work.

This is just a plastic 1/4" 90



The modification of the bell adapter in the mill, drilling a 5/16" hole.



The fitting pressed into the bell adapter



Bell adapter installed with new vent hose attached.



Clearance with the OEM filter



Clearance with a SW base plate

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Old 08-27-2013, 10:19 PM   #9
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Thumb

After a day of building virtual systems that are highly available to present a collaborative web application I needed some LC8 intimate time

Since I was starting from only a hunch of what MIGHT work I got to do 3 iterations in about 1.5 hours

iteration 1: it does what is should when cold... it needed full enrichment to start and was to slow idle and off enrichment in about 1 minute. Street dyno says low speed and mid steady state is good, tip in stumbling, wont rev beyond 5 k without coaxing.

iteration 2: pulled back main jet sizes to OEM (155/160), re-test.... its worse in the mid, can't get it past 5k without major complaining from the engine.... I now have a direction to go in, one of the good things about making a BIG change to ONE circuit.

iteration 3: kitchen sink approach left the pilots alone, dropped the float height by 1mm, installed FP needles at #2, and WENT BIG with the mains.... and the result?

It RUNS pretty damn good! Idle and low speed is 'refined', no major poping on decel, not knife edged response on throttle input. Wack WFO at 3500 in 2nd and it doesnt explode like my other prefilter tune (bummer), but definitely pulls hard and jumps through to 8k plus pretty well, feels strong in the 5k to 8k range. Stumbles on fast tip in when 5k low load then clears up and runs through. It started to rain and it was dark, so I didn't push it much. I also want to make sure that the fuel is fresh since the bike has been sitting for 3+ months before I do much more alterations. I think that I'm going to try going to #3 on the needles and see if it clears up the mid RPM tip in stumble. If it shows me that this is the direction I may try one or two other changes.... Next idea is to mount WBO2 and start logging.

It is not perfect, it needs refinement, but its not too bad for a couple hours of seat of the pants EWAG tuning
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Old 08-27-2013, 11:15 PM   #10
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Suppose you could have an air pump connected to a sealed chamber in which the carb vents end.
Suppose also that by some electronic means and sensors you could vary the air pressure in that chamber at will according to the engine needs for optimum performance.
What would you want this pressure 'ideally' to do? Be constant or vary and how?
External conditions could include crosswinds or altitude variations.


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Old 08-28-2013, 07:31 AM   #11
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Originally Posted by mousitsas View Post
Suppose you could have an air pump connected to a sealed chamber in which the carb vents end.
Suppose also that by some electronic means and sensors you could vary the air pressure in that chamber at will according to the engine needs for optimum performance.
What would you want this pressure 'ideally' to do? Be constant or vary and how?
External conditions could include crosswinds or altitude variations.

Honestly I don't see the long term benefit of a highly complex bowl venting system as you suggest.
My goals are:
1. Solve the highly sensitive bowl venting issue
2. vent bowls in a simple manner.

I believe that I have achieved goal 2 by utilizing the 90 hose fitting and venting the bowls to the air jet area of the carbs. I do not know if I have achieved the first goal yet as I have not spent enough time with the bike in every condition.

I need to try to get it to run the way that I want it to, similar to the Prefilter setup and/or the open foam setup, then move forward with testing the crosswind performance. It is not that far off right now, ultimately I will need to put it through its paces with road/butt dyno testing with full instrumentation to see if I can make it work. I have a short opportunity window before I need to move on and shelve it for a later date and time, so I am hoping that the next 1 to 2 iterations are good enough to run it for a longer period of time to test fuel consumption.
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Old 08-28-2013, 09:02 AM   #12
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Originally Posted by Head2Wind View Post
Honestly I don't see the long term benefit of a highly complex bowl venting system as you suggest.
My question was probably more convoluted than necessary. I was actually not suggesting to do something like that, but your answer would give me a very clear idea as to what we actually want from the bowl venting.

In other words, what are the ideal pressure conditions at the end of the venting lines? Is it better for it to be the same for all altitudes eg 1 atm, or is it better if it follows the atmospheric pressure of whatever altitude we currently are?
Or would it actually be perfect if we could control it automatically , because in this way we could (maybe) achieve near perfect carburation at any altitude?
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Old 08-28-2013, 10:43 AM   #13
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Originally Posted by mousitsas View Post
In other words, what are the ideal pressure conditions at the end of the venting lines? Is it better for it to be the same for all altitudes eg 1 atm, or is it better if it follows the atmospheric pressure of whatever altitude we currently are?
Or would it actually be perfect if we could control it automatically , because in this way we could (maybe) achieve near perfect carburation at any altitude?
Based upon the conversation that I had with Marc and his experience with a different motorcycle that was very sensitive, to the point where if you blew air across the intake snorkel of the air box the engine would die, his conclusion (and solution for that motorcycle) was that the bowl pressure needed to equal the POST filtered pressure (answer to your first question). Many of the non-fuel injected 'ram air' street motorcycles vent the bowls to the airbox so that they do not go lean at speed.

Based upon my experience so far along with Marc's the answer to your second question is answered by my first conclusion, the POST filtered atmospheric pressure is what the bowl pressure should equal for all conditions.

My intention is to try to apply this methodology to the carb'd LC8 with any iteration of the OEM airbox and filtering systems, specifically in this case OEM airbox/paper filter/ADVmachines Prefilter.

It is not my intention to try to emulate a ECU monitored absolute pressure sensor and apply a fuel table like a EFI system does. Many US auto manufacturers applied this to the 'pre fuel injection' carburation in the 80s. They sucked badly.

As much as it would be nice to have the carburation self adjust for environmental conditions, it has been proven to be possible, however the systems required are complex and tend to fail easily.
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Old 08-28-2013, 11:02 AM   #14
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Originally Posted by Head2Wind View Post
Based upon the conversation that I had with Marc and his experience with a different motorcycle that was very sensitive, to the point where if you blew air across the intake snorkel of the air box the engine would die, his conclusion (and solution for that motorcycle) was that the bowl pressure needed to equal the POST filtered pressure (answer to your first question). Many of the non-fuel injected 'ram air' street motorcycles vent the bowls to the airbox so that they do not go lean at speed.

Based upon my experience so far along with Marc's the answer to your second question is answered by my first conclusion, the POST filtered atmospheric pressure is what the bowl pressure should equal for all conditions.

My intention is to try to apply this methodology to the carb'd LC8 with any iteration of the OEM airbox and filtering systems, specifically in this case OEM airbox/paper filter/ADVmachines Prefilter.

It is not my intention to try to emulate a ECU monitored absolute pressure sensor and apply a fuel table like a EFI system does. Many US auto manufacturers applied this to the 'pre fuel injection' carburation in the 80s. They sucked badly.

As much as it would be nice to have the carburation self adjust for environmental conditions, it has been proven to be possible, however the systems required are complex and tend to fail easily.
Very informative clear and I feel covered! Thanks Ken.

But....isn't that what our bikes came stock with? Venting tubes with a Y through the lower box, up the snorkel, ending on the top of the airbox, post filter?

Could the ITG/CPR dudes install a nipple on the base plates to do the same using the stock Y venting lines?
Would that throw off jetting?

No more questions, I promise!
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Old 08-28-2013, 12:26 PM   #15
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Originally Posted by mousitsas View Post
Very informative clear and I feel covered! Thanks Ken.

But....isn't that what our bikes came stock with? Venting tubes with a Y through the lower box, up the snorkel, ending on the top of the airbox, post filter?

Could the ITG/CPR dudes install a nipple on the base plates to do the same using the stock Y venting lines?
Would that throw off jetting?

No more questions, I promise!
But....isn't that what our bikes came stock with? Venting tubes with a Y through the lower box, up the snorkel, ending on the top of the airbox, post filter?

~~~~~~~~~~for the SE this is partially true, however the other portion of the venting goes down into a vacuum controlled valve that is held at something below ambient atmospheric pressure to draw fuel vapors through the carbon canister and then into the intake manifold. For all of the ADVs from the factory they were either to atmosphere (early) or to a evap system.~~~~~~~~~~~

Could the ITG/CPR dudes install a nipple on the base plates to do the same using the stock Y venting lines?

~~~~~~~~~~Yes, however it will not work well because liquid fuel will pool/collect at the low point and block air flow~~~~~~~~~~


Would that throw off jetting?
~~~~~~~~~~~YES!~~~~~~~~~~

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