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Old 11-05-2012, 08:01 AM   #46
kamanya
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Something I wanted to ask those of you who have these carbs.

I can't get past 200kph. I hardly ever go there, especially as I have Michelin deserts on, but recently I found something that was of interest in this conundrum.

I currently run a 17/42 only because that's what I needed when I had the SD gearing in. Now I have the standard Adv gearing, it's much better but just waiting for a spot of garage time to go down in sprockets. But, the current gearing with my 100 plus Hp should be a breeze, literally. But it's not.

Initially, I put it down to the 39mm's just not being up to the task when in higher revs, but now that I have dropped the gearing I still end up with the same terminal velocity even though the engine is now sitting in the meat of it's torque?

Last week I was going up a pass that is renown for it's wind. It is a freeway type thing with long wide corners that can be taken at speed. This day was especially windy. I noticed on one long sweeping corner, that as the wind angle changed more from side on, to the front, the bike lost a noticeable amount of power. Not suddenly, just in relation to the angle of the wind. I turned around and rode up there twice just to check I was not imagining it.

I think that up to 170kph'ish, the carbs do not get so affected by wind blast, once past that there must be something going on that affects the flow. I have safari tanks on, maybe they funnel more air in that disturbs the flow. I am keen to know if any of you can easily get past 200 with your FCR's on an Adventure format bike?

I am looking forward to my set of billet velocity stacks to see if it makes a difference. I also suppose that the airbox on the OEM carbs may have a role to play in shielding the carbs from the adverse effects of the wind blast.
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Old 11-05-2012, 10:40 AM   #47
crofrog
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Quote:
Originally Posted by kamanya View Post
Something I wanted to ask those of you who have these carbs.

I can't get past 200kph. I hardly ever go there, especially as I have Michelin deserts on, but recently I found something that was of interest in this conundrum.

I currently run a 17/42 only because that's what I needed when I had the SD gearing in. Now I have the standard Adv gearing, it's much better but just waiting for a spot of garage time to go down in sprockets. But, the current gearing with my 100 plus Hp should be a breeze, literally. But it's not.

Initially, I put it down to the 39mm's just not being up to the task when in higher revs, but now that I have dropped the gearing I still end up with the same terminal velocity even though the engine is now sitting in the meat of it's torque?

Last week I was going up a pass that is renown for it's wind. It is a freeway type thing with long wide corners that can be taken at speed. This day was especially windy. I noticed on one long sweeping corner, that as the wind angle changed more from side on, to the front, the bike lost a noticeable amount of power. Not suddenly, just in relation to the angle of the wind. I turned around and rode up there twice just to check I was not imagining it.

I think that up to 170kph'ish, the carbs do not get so affected by wind blast, once past that there must be something going on that affects the flow. I have safari tanks on, maybe they funnel more air in that disturbs the flow. I am keen to know if any of you can easily get past 200 with your FCR's on an Adventure format bike?

I am looking forward to my set of billet velocity stacks to see if it makes a difference. I also suppose that the airbox on the OEM carbs may have a role to play in shielding the carbs from the adverse effects of the wind blast.

How do you have your carbs vented?
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Old 11-05-2012, 11:12 AM   #48
kamanya
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Originally Posted by crofrog View Post
How do you have your carbs vented?
Hmmm, I hadn't thought of that.

All 4 are routed to the left and are bunched and zip tied to the frame ending near my left calf.
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Old 11-05-2012, 12:24 PM   #49
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Hmmm, I hadn't thought of that.

All 4 are routed to the left and are bunched and zip tied to the frame ending near my left calf.
On the adventure you run the carb vents into the center of the V on the engine there is nice calm air there.

I think the SE had some additional plumbing to let the carbs vent during deep water crossings too.

http://www.ktm950.info/how/Orange%20...carb_vents.jpg
"the Super Enduro (see photo by firebolter) has an extra set of carb vent hoses that run from a brass "L" on the opposite side of each carb to a "Y" and a single line out the snorkel and into the A/C cover. This is to provide proper function of the carb vent system in deep water crossings."


and the desert bikes had
http://www.ktm950.info/how/Orange%20...utch_mods.html
"Drill a 2mm hole into the top of the black 90 degree elbows where the fuel vent lines are connected. This helps avoid flooding the bike in case of a crash. For desert racing, it’s better to run the vent lines up under the steering stem and fitted with a small filter."

Obviously the plumbing on the FCR is going to be different, but I think specially with the cross wind you where talking about that it's likely going to be a carb venting issue causing the bike to run either rich or lean.
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Old 11-05-2012, 12:41 PM   #50
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I, too, have hit the "wall" with my FCR's and kit pods. There is a point where I cannot make more RPMs, at high travel speed, and I know the RPMs are available in lower gears, from the rev limiter engagement. Could it be that we are so aerodynamically "effecient" that there is no way to press that envelope further, without some valances or displacement? The intake restriction of the standard airfilters may be showing itsself, at that point.

I have direct frontal air into the pods and don't have any lateral wind pressure changes noticibly affecting engine output. I get steady throttle RPM hunting with wind changes, but I attribute it to the venting.

edit to add: jetting is a bit fat as well, in my case, could be the last few hundred heavy loaded RPM that needs a leaner main.
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Old 11-05-2012, 08:21 PM   #51
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Originally Posted by snowhawk jockey View Post
I, too, have hit the "wall" with my FCR's and kit pods. There is a point where I cannot make more RPMs, at high travel speed, and I know the RPMs are available in lower gears, from the rev limiter engagement. Could it be that we are so aerodynamically "effecient" that there is no way to press that envelope further, without some valances or displacement? The intake restriction of the standard airfilters may be showing itsself, at that point.

I have direct frontal air into the pods and don't have any lateral wind pressure changes noticibly affecting engine output. I get steady throttle RPM hunting with wind changes, but I attribute it to the venting.

edit to add: jetting is a bit fat as well, in my case, could be the last few hundred heavy loaded RPM that needs a leaner main.
Your float bowls may be running dry of fuel at high demand/steady full throttle. The stock 9mm setting doesn't work so well with the FCRs tilted so far forward as on the 950/990. I set mine to 7.5 mm to compensate.

I don't really ever ride at 200kph, so I have no idea if this would make a difference in that regard, but it's worth investigating.
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Old 11-05-2012, 08:37 PM   #52
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Originally Posted by Flanny View Post
Your float bowls may be running dry of fuel at high demand/steady full throttle. The stock 9mm setting doesn't work so well with the FCRs tilted so far forward as on the 950/990. I set mine to 7.5 mm to compensate.

I don't really ever ride at 200kph, so I have no idea if this would make a difference in that regard, but it's worth investigating.
Never considered that angle in the tuning for my "reasonable and prudent" use of the throttle. I felt fortunate to not get much bogging in the whoops and now will be testing the balance of that, with the mysterious drying bowl question. Thanks for the spec to work from!
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Old 11-05-2012, 11:57 PM   #53
kamanya
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I'll wait for the velocity stacks to arrive and put the recommended jetting in for them before I start fiddling with the carbs again.

Snowhawk, do you have a filter in the fuel line anywhere? I have one before the facet pump. I might just change that to eliminate that variable too.
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Old 11-06-2012, 06:07 AM   #54
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With a wide band you should be able to tell if the fueling ends up being off at high RPM. Might be worthwhile to install one and make your tuning allot easier an EGT could be useful too.

Target between 12.8 to 13.0 on the AFR for peak power.
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Old 11-06-2012, 09:51 AM   #55
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Originally Posted by crofrog View Post
With a wide band you should be able to tell if the fueling ends up being off at high RPM. Might be worthwhile to install one and make your tuning allot easier an EGT could be useful too.

Target between 12.8 to 13.0 on the AFR for peak power.
True, a sensor would take the guess work out of that level of tuning. Plus I am fortunate to have 990 headers, with the sensor bungs, hanging off the motor.

Quote:
Originally Posted by kamanya
I'll wait for the velocity stacks to arrive and put the recommended jetting in for them before I start fiddling with the carbs again.

Snowhawk, do you have a filter in the fuel line anywhere? I have one before the facet pump. I might just change that to eliminate that variable too.
I am stock fuel pump and no filter in the line.
My interim fiddling will be with the TPS, so I can get the right advance for start up. Saving the float adjustments for after the trumpets arrive.

Heck riding season is winding into the cold, so I'm in no rush...
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Old 11-06-2012, 10:09 AM   #56
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Originally Posted by kamanya View Post
...a filter in the fuel line anywhere? I have one before the facet pump. I might just change that to eliminate that variable too.
If you can hit Red Line, with no problems, then the Fuel Filter should not be a problem.

I think the Carb Venting at high speed is where it is happening.

AdvGa screwed with this post 11-06-2012 at 02:02 PM
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Old 11-06-2012, 11:29 AM   #57
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If you can hit Red Line, with no problems, then the Fuel Filter should be a problem.

I think the Carb Venting at high speed is where it is happening.
I am tempted to go with a catch can to stabilize the airpressure on the vent sys. I had a similar effect on the EXC when I put the catch can, more consistant venting(until the catch can got a load of gas in it...)
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Old 11-06-2012, 12:49 PM   #58
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Is it possible it's just a matter of wind resistance? The 950A is a bit of a barn aerodynamically.

IIRC the highest speed I've heard of for the Adv was 130mph-ish - which is only a touch above 200kmh. (and that was no wind, on a salt flat, no screen and no seat so the rider could get lower...)

Wind resistance is a function of the square of velocity (if my memory of physics serves me...)
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Old 11-07-2012, 12:24 AM   #59
kamanya
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Originally Posted by mookymoo View Post
Is it possible it's just a matter of wind resistance? The 950A is a bit of a barn aerodynamically.

IIRC the highest speed I've heard of for the Adv was 130mph-ish - which is only a touch above 200kmh. (and that was no wind, on a salt flat, no screen and no seat so the rider could get lower...)

Wind resistance is a function of the square of velocity (if my memory of physics serves me...)
My old 950 with OEM carbs easily broke 200. 218 was where it stopped on the flat, no wind.

On a deserted Karoo desert road I had "slowed a bit" to take this in 2007 on;

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Old 11-07-2012, 11:50 AM   #60
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Originally Posted by mookymoo View Post
Is it possible it's just a matter of wind resistance? The 950A is a bit of a barn aerodynamically.

IIRC the highest speed I've heard of for the Adv was 130mph-ish - which is only a touch above 200kmh. (and that was no wind, on a salt flat, no screen and no seat so the rider could get lower...)

Wind resistance is a function of the square of velocity (if my memory of physics serves me...)
The aerodynamics are always my excuse for why the back tire just spins up(on dirt) and the bike doesn't gain KPH on the speedo, above the "terminal velocity" of our coefficient of drag.

edit to add:
I have seen +/-113mph on the GPS with 16/45 gears, on a 17" rear. Keep in mind that was paved and I have never been able to get above +/-105mph on the dirt, same setup. My GPS crapped out and I haven't been able to GPS 17/45 or 16/42, just speedo'd and that # is questionable...

snowhawk jockey screwed with this post 11-07-2012 at 11:57 AM
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