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Old 02-14-2006, 08:21 PM   #1
Billroy OP
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Thumb Beware of adding filter to carb vents (after canisterectomy)

Just thought I would share the problem I had:

When I bought the bike I performed the canisterectomy and removed the SAS successfully. At the time, after researching most threads on the canisterectomy it seemed that most people were reporting success with fitting some form of filter on the carb vents just below the airbox to prevent possible dirt from finding it's way up the vent hose and into the carbs. I added a small fuel filter (metal exterior with paper filter interior) just after the Y in the carb vents right below the airbox.

After doing this I enjoyed a nice long 3+ hour ride in the mountains around Calgary with excellent performance (no surging despite high winds) so I thought nothing more about it.

Next I added staintune exhaust and raised the stock needle one clip and went for good long test ride. Good performance except for a low-end (first 1/4 throttle) bog but otherwise acceptable.

Next I added a 45 pilot and put the stock needle back to clip 2 and went for a test ride. Outstanding performance. The bike was flying like a homesick angel and then after 15 mins into my ride upon landing the front wheel after a great power wheelie the engine just suddenly died. I cranked and cranked and finally the engine sputtered to life and began backfiring and spitting something fierce before finally dieing again. I trailered the bike home and didn't have a chance to look at it as I was late for another engagement now.

The next day I went into my shop and the bike fired right up so I figured it must have been the much-talked-about tank vent issue so I removed the one-way tank vents (top) that I had installed in case they may have clogged, removed both tanks and checked to make sure I wasn't kinking the lower tank vents or fuel supply hose and reinstalled. I went for another ride and this time, only 5 minutes into the ride with unbelievable performance, again after landing from a wheelie the engine just died instantly. I opened the tank caps, checked the fuel petcocks and cranked and cranked til the battery died. I pushed the bike home as I had stayed close this time.

I spent a sleepless night trying to figure out what it could be that would cause a bike to die after a wheelie. Surely it couldn't be some demon KTM installed in the bike to keep people from stunting or killing themselves... sales would plummet.

I went through all the things I had done to the bike. Exhaust change: that wouldn't cause great performance followed by death after 15 mins. Jetting: usually jetting will let you know right away if your changes are correct -not after 15 minutes and not by a sudden stall. Canisterectomy: I had done this several rides before, why would it come back to haunt me now? Then it hit me.

The bike was dieing exactly the same way my previous dirt bike (honda crf450R) did when I tried to ride through a creek more than 10" deep. Only one tank vent hose hanging down below the bike and as soon as it touched water the engine died. Bingo.

The next morning I took the right tank off, reached under the airbox and cut off the filter that I had installed on the tank vent hose. I blew on the filter and it was hard to blow until a big slosh of fuel spurted out. In the garbage it went. Now the carbs are vented to atmosphere just below the airbox.

The bike runs great - even after wheelies! Throw the carb vent filter in the garbage if you have one installed because it will clog. Remember the carb vent is also an overflow and the overflow can cause the filter to clog, creating the same scenario you were trying to avoid by performing the canisterectomy in the first place.
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Old 02-14-2006, 09:24 PM   #2
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Thanks for sharing, and very nicely writen. I feel the same about the vent above the tanks that connect under the head light. Get rid of the filters and let the sucker breath. On a very hot ride down Copper Canyon with two other 950s (all w/ the canisters removed). Two of the 950s w/ fuel filters on the end of there breather hose were puck'n out fuel, and the one (mine ) opened and able to breath didn't lose a drop. It was never proven that the filters were the cause of the problem, but it sounds like a good guess to me.
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Old 02-14-2006, 09:27 PM   #3
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Nice piece of info, thanks. I always wondered why people put a filter on their carb vents, when someone rightly spoke about the non filtered carb vents on the dedicated dirt bikes in the KTM and other marques range. Made sense to me, mine run without - and perfectly

Interesting that you got more joy out of a 2nd needle position as opposed to third. Any thoughts why? (I run Akras without baffles and wonder if I should do same to help out with really pee poor fuel economy)
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Old 02-15-2006, 07:13 AM   #4
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Quote:
Originally Posted by LiveInTheOutdoors
Nice piece of info, thanks. I always wondered why people put a filter on their carb vents, when someone rightly spoke about the non filtered carb vents on the dedicated dirt bikes in the KTM and other marques range. Made sense to me, mine run without - and perfectly

Interesting that you got more joy out of a 2nd needle position as opposed to third. Any thoughts why? (I run Akras without baffles and wonder if I should do same to help out with really pee poor fuel economy)
That could have been me http://www.advrider.com/forums/showt...49#post1934649

The needle in the stock position works. Moving it stuffs everything. You can control needle mixture by changing the main jets. The #45 pilot and stock needle should form the basic jetting package with alterations to the mains to get it right for your bike.

These things are way to rich on the mains. Thats why the fuel figures are so poor. I'm running 140, 142.5 and I am still rich. I will go down another half step to 137.5, 140.

My fuel light came on at 265km. My fill tonight was 325km - 21.5 Lt (all city)
15.1 km Lt
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Old 02-15-2006, 08:03 AM   #5
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Quote:
Originally Posted by Billroy
I added a small fuel filter (metal exterior with paper filter interior) just after the Y in the carb vents right below the airbox.
Are these the vent lines that come out of the top of the carbs... ...if so, I think see your problem
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Old 02-15-2006, 09:49 AM   #6
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Seems like that's what he's talking about. In which case you really should have something filtering the vent. Because, as I understand it, the vent draws air and anything else at the end of it INTO the carb. It might also serve as an overflow but why would it overflow? You flooded the carbs? I might suspect that the filters that you used were too constrictive and when the carbs couldn't breathe properly fuel was sucked, venturi? , down into the vent tube.

Heh, I'm by far not qualified to tell you what happened or why. It just kind of seems logical to me.

Here's what I did.

I took 3 zip ties and a small piece of air filter foam like this.



Then I ran a vent hose from the Y in the airbox out the bottom to the back of the airbox where I did this.



This should filter anything going in and not be too constrictive either way. Cheers
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Old 02-15-2006, 11:24 AM   #7
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Quote:
Originally Posted by Motobrandt
snip...It might also serve as an overflow but why would it overflow? ...snip Cheers
It might have sometning to do with the wheelies.
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Old 02-15-2006, 01:09 PM   #8
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Quote:
Originally Posted by Motobrandt
Seems like that's what he's talking about. In which case you really should have something filtering the vent. Because, as I understand it, the vent draws air and anything else at the end of it INTO the carb.
I could be wrong, but it don't think it's that critical.
If the vent is there to allow the slides to raise/lower, aren't they in effect just acting like a snorkel and push/pulling the same volume of air?
As the slides rise, they allow the air above them to be expelled, as they lower, they allow the air back in avoiding a vacuum that would halt or drastically reduce the speed at which they drop.
I think that's the reason they need to be vented to atmosphere. If terminated in the air box, the slides will be affected by the carbs sucking the air through the filter. Vented to an area with lots of turbulance has a similar effect and can cause surging no?
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Old 02-15-2006, 02:31 PM   #9
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Motobrandt continues to make this classic mistake and one day it will bite him. This is what you should not do! First time he drops his bike he will get a puddle of fuel sitting in the low spot of the hose effectively blocking this atmospheric balancer (breather)
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Old 02-15-2006, 02:41 PM   #10
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Quote:
Originally Posted by K2m
Motobrandt continues to make this classic mistake and one day it will bite him. This is what you should not do! First time he drops his bike he will get a puddle of fuel sitting in the low spot of the hose effectively blocking this atmospheric balancer (breather)
LOL!!!

Thanks for the tip mate! But continues? this would be the first time I made this this classic mistake. And thanks to your kind words I will go and make sure that the tube flows downhill then it will not bite me. Makes sense to me.

Have a nice day.

Should my whole response have been in bold?
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Old 02-15-2006, 02:45 PM   #11
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Quote:
Originally Posted by Ant Ware
I could be wrong, but it don't think it's that critical.
If the vent is there to allow the slides to raise/lower, aren't they in effect just acting like a snorkel and push/pulling the same volume of air?
As the slides rise, they allow the air above them to be expelled, as they lower, they allow the air back in avoiding a vacuum that would halt or drastically reduce the speed at which they drop.
I think that's the reason they need to be vented to atmosphere. If terminated in the air box, the slides will be affected by the carbs sucking the air through the filter. Vented to an area with lots of turbulance has a similar effect and can cause surging no?
Thanks Ant. I looked a lot through all of the many pages of SAS and canisteractomy threads and such. I never did find a definitive answer. Some say use a filter even specifying the 640 filter. I just didn't know what to think of it all. So I thought I'd penny tech something together do you think that the air in and out is so sensitive that that little bit of foam would restrict it?
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Old 02-15-2006, 03:00 PM   #12
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There is a description on another thread. I will try to find it. Also a service bulletin on an factory upgrade to these breathers (Non US)
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Old 02-15-2006, 04:40 PM   #13
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I don't know how many times I have explained this, but here goes again...

The carb vents are vented to atmosphere. As such, they are subject to dust getting in, and eventually mucking up your slide if you don't run a filter.

There are two possible solutions, and then the right solution.

1) Run a long vent line down to the bottom of the bike to prevent dust from finding it's way in. This is the classic way most vents cause dying bike when entering water.

2) Put a filter on the end of a short vent to allow it to breath. This will lead to the problem of fuel or crank-vent oil "puddling" in the vent line, and causing the described problem.

The RIGHT way to do this, is actually to do BOTH. Run the carb vents together into a "Y" connector, and then after a short tube into a "T". On the bottom of the "T", run a long hose out to the bottom of the bike to drain fuel/oil when it does get in there. Then run a filter on a short piece of tube on the other side of the "T". Voila - Filtered carb vent AND no fuel puddling!

I'm not sure why this is so confounding to everyone...this has been done on dirt bikes since Christ was a choir-boy. The 950 is no different!
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Old 02-15-2006, 04:46 PM   #14
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KTM delivered the Aussie bikes with separate vent lines. Apparently they don't care about making ozone holes over in Oz, I don't either.


Front carb vent added upper left. Drain just above it RTVed shut, excess OEM vent hole tolerance now serves as airbox drain. The cross sectional area of the U.S. speced Y connection is 40% less than the two fuel lines that service it.
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Old 02-15-2006, 05:09 PM   #15
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Quote:
Originally Posted by Flanny
The RIGHT way to do this, is actually to do BOTH. Run the carb vents together into a "Y" connector, and then after a short tube into a "T". On the bottom of the "T", run a long hose out to the bottom of the bike to drain fuel/oil when it does get in there. Then run a filter on a short piece of tube on the other side of the "T". Voila - Filtered carb vent AND no fuel puddling!

I'm not sure why this is so confounding to everyone...this has been done on dirt bikes since Christ was a choir-boy. The 950 is no different!
Well some of us less fortunate humans are learning about dirt bikes and the way that this singing christ guy did things as we read, search and type. Sometimes wading through the hundreds of posts about canisterctomy stuff is less then obvious. Here's a good example.

Quote:
Originally Posted by Flanny
Here's what I did.

Canister
1 - I removed the Charcoal Canister and the vaccum valve from the fairing.
2 - I removed the vaccum valve from under the air box
3 - I installed a peice of hose from the "Y" fitting between the carbs (the carb vents) and ran it to behind the airbox where the SAS valve was, and connected it to a carb vent filter from a 640 Adventure.
4 - I vaccum capped all vaccuum ports on the intakes.
5 - I vented the fuel tanks using 1/4 fuel line by simpoly running the line down along the fram trellis to meet with the overflow hose, and ran it down parralel to the overflow.
Thanks for the definitive answer Flanny. I love learning about dirt bikes. Especially the ridiculously large ones.
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