Filter on carb


15 replies to this topic
  • Thirdear1

Posted October 30, 2007 - 02:43 PM

#1

So why hasn't anyone run a filter right off the carb? I can understand that sure if you're planning on water applications then it might not be the best choice but if just dusty or street conditions apply then why not?

  • cleonard

Posted October 30, 2007 - 03:24 PM

#2

The carb and the airbox are designed as a system. The airbox causes some pressure drop and this effects the jetting a lot more than you might think. Usually the required jetting changes can't be taken care of by just pilot and main jet increases. The needle needs changing to a much richer profile.

With enough jetting effort some top ends gains are possible.

  • martinfan30

Posted October 30, 2007 - 08:50 PM

#3

when i did my battery relocation to the airbox i had to run a uni pod filter. it was hard to get the stock cv carb jetted right to get rid of a 1/3 throttle hesitation.. never did get it resolved until i bought a fcr 41 pumper. with just main and pilot changes i was able to get the pod filter/fcr to work perfectly. has great top end. bottom and mid didnt change. now i just put in the hotcam stage 1 so tommorrow im sure i will have to rejet after breaking in the cam.

the pod filter is great for street and on dirt(just have to be sure to clean OFTEN!) which is pretty easy and done anyways. just be carefull of deep water.

  • Denn10

Posted October 30, 2007 - 08:59 PM

#4

howd ur cam thing go

  • Thirdear1

Posted November 03, 2007 - 01:21 PM

#5

alright so the airbox and carb work together, so why isn't it possible to just stick the filter on the carb and make it work, other dude did it, granted with another type of carb, but how different can they all be?:worthy: maybe i just don't understand the dynamics of the airflow? is that it? what's different in this scenario? that said the other guy moved battery to airbox, which seems like a prety cool idea, eliminate excess weight from rear and clean up lines? maybe something i'd like to do too,......how do the one's that win races have their stuff setup??

  • Thirdear1

Posted November 03, 2007 - 01:22 PM

#6

alright so the airbox and carb work together, so why isn't it possible to just stick the filter on the carb and make it work, other dude did it, granted with another type of carb, but how different can they all be?:worthy: maybe i just don't understand the dynamics of the airflow? is that it? what's different in this scenario? that said the other guy moved battery to airbox, which seems like a prety cool idea, eliminate excess weight from rear and clean up lines? maybe something i'd like to do too,......how do the one's that win races have their stuff setup??

  • creeky

Posted November 03, 2007 - 04:48 PM

#7

A few years ago, I built an XR600 engine for a friend that races flat track. I installed a universal (round straight type) K&N filter directly on the carb (Edlebrock), worked great.

  • Norge

Posted November 04, 2007 - 02:47 PM

#8

alright so the airbox and carb work together, so why isn't it possible to just stick the filter on the carb and make it work, other dude did it, granted with another type of carb, but how different can they all be?:worthy: maybe i just don't understand the dynamics of the airflow? is that it? what's different in this scenario? that said the other guy moved battery to airbox, which seems like a prety cool idea, eliminate excess weight from rear and clean up lines? maybe something i'd like to do too,......how do the one's that win races have their stuff setup??


I have the battery and fuses relocated to the airbox also. Have a UNI pod installed on a flat slide Mikuni. Works great, no issues.

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  • martinfan30

Posted November 05, 2007 - 08:17 AM

#9

the problem is with the stock CV carb. they dont like the change made to the intake. hard to jet the 1/3 throttle hesitation out. hence, the flat slide.
heres pics of my mod. bottom is all the excess pork.

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  • cleonard

Posted November 05, 2007 - 09:47 AM

#10

It's easy to get top end gains. It is the low to midrange that suffer. You are going to need an assortment of jets. In my area Cycle Gear sells jets for $2.99 each and the dealer $5. You should be able to get idle and top end right with just jets. I've never done one of these bikes, but on an old street bike project I had to go from a 118 main to about 140. That bike had a very restrictive airbox, so I don't think that the change will be so extreme for an XR.

The needle controls the mid range. This is the toughest part to get right. I would start off by moving the needle to the max rich position. If that is not rich enough there should be aftermarket needles available. Which bike are we talking about (XR600, XR650l, XR650r)? Eddie over in the jetting forum might know if there are richer needles available and even which one to try.

It is possible to run a pod, it's just hard to get it as smooth as the stock setup.

  • Norge

Posted November 05, 2007 - 10:35 AM

#11

[quote name='martinfan30']the problem is with the stock CV carb. they dont like the change made to the intake. hard to jet the 1/3 throttle hesitation out. hence, the flat slide.
heres pics of my mod. bottom is all the excess pork.


Looks like our pigs went through identical diet plans. An XR600 side panel will eliminate that left side hump where your batt was at.:worthy:

  • martinfan30

Posted November 05, 2007 - 11:24 AM

#12

[quote name='Norge'][quote name='martinfan30']the problem is with the stock CV carb. they dont like the change made to the intake. hard to jet the 1/3 throttle hesitation out. hence, the flat slide.
heres pics of my mod. bottom is all the excess pork.


Looks like our pigs went through identical diet plans. An XR600 side panel will eliminate that left side hump where your batt was at.:worthy:[/QUOTE]


you got a pic?

  • Thirdear1

Posted November 05, 2007 - 06:35 PM

#13

love the forums!! y'all are awesome, really no better place for info, went into bookstore yesterday to see if there were any mags on this stuff, saw the price of something like 5 bucks for simple mag and was like,, screw this .. i'll just keep reading what these guys have done,,, i'll get it right...... all i can say is god bless america for this stuff,,,,,really great tool... y'all are awesome

  • Norge

Posted November 05, 2007 - 06:38 PM

#14

Posted Image

Here is an XR600 side cover from Aceribis.

  • Thirdear1

Posted November 05, 2007 - 06:40 PM

#15

hey though, as home boy once said, if you go stick this foam air filter in there, she back fires and your filter is toast, what are you supposed to do? or does the jetting resolve the backfires? i took off the smog stuff and the back fires are still just about the same, i guess the factory paper filter is immune to this? what else am i missing here?

  • martinfan30

Posted November 05, 2007 - 09:07 PM

#16

hey though, as home boy once said, if you go stick this foam air filter in there, she back fires and your filter is toast, what are you supposed to do? or does the jetting resolve the backfires? i took off the smog stuff and the back fires are still just about the same, i guess the factory paper filter is immune to this? what else am i missing here?


once i rejetted my cv carb i had zero backfiring. then rejetting my current fcr i have zero backfiring through the intake. its ALL about the right jetting.

ive never heard of a correctly running 650L backfiring through the intake and burning a filter. although anything is poss. i guess!





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