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Discussion Starter #1
After very extensive dyno testing on the KTM SX ATV, we developed a way to ELIMINATE the dreadful bog that we all have experienced on our machines. We are actively working on the XC, and should have information out on it shortly

WARNING:
USE THIS INFORMATION AT YOUR OWN RISK; WE AREN’T RESPONSIBLE FOR ERRORS IF YOU DECIDE TO PERFORM THESE MODIFICATIONS YOURSELF. THIS INFORMATION IS SOLELY PROVIDED AS A GUIDE. PROCEED WITH EXTREME CAUTION!!!

#1 Leak Jet Installation

To address the lack of adjustability of the accelerator pump we drilled & tapped the bowl for a leak jet. The leak jet allows us to address how far & long the accelerator pump squirts. We found that a #40 leak jet performed the best.

#2 Increase Accelerator Pump Squirt Nozzle Diameter

The next modification we made was to drill the accelerator pump squirt nozzle larger. From the factory the accelerator pump nozzle has a 0.013” opening. We found that by carefully drilling it to 0.016” (approximately 23% larger) it helped make the accelerator pump easier to tune and much more effective.

#3 Replace OEM Pilot Jet

From the factory the #42 pilot jet is too small. To fix this we simply replaced it with a #45 pilot jet. This corrected the minor idling issues especially when the engine is cold. This is very simple and easy to do.

#4 Replace OEM Needle

The factory needle’s taper is too narrow at the tip which creates a lean issue from 3/4 throttle to wide open throttle (WOT) as well as the incorrect main jet being used. To cure this we replaced the needle with a needle found in the Honda HRC kit; it allowed us then to install the correct main jet.

#5 Install O-ring

Add the O-ring mod to the accelerator pump. The O-Ring size/number is 010

Drilling the leak jet & squirt nozzle are NOT recommended unless you have experience in dealing with 0.001” tolerances. Not to mention the drill bits are typically special order items.

If you send us the entire carb, we charge $125 to drill/tap the bowl for a leak jet & drill the squirt nozzle (return domestic shipping included). Active subscribing (paid) members to KTMATVHQ.com only pay $110! (Parts included),

I am in the process of getting some bowls & squirt nozzles ready to go so I can offer them as a “kit” with or without a core charge. Unfortunately, I don’t have any kit pricing available right now.



Fast64Ranchero & Driver311
 

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My bike runs flawless with this work done. I was super stoked, the bike had a crazy bog down low and we could not tune it out, once the exhaust system was on. This mod is a must.
 

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Good write up! I know this will be on my list of things to get done :) Good job on the R&D on this! Also a person could pay to have the R&D bowl, but you would still need the drilling done. So this is a win win fix !
 

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You can also spend 250 dollars for a new R&D float bowl that comes with the needle that they drill and the leak jet.AND I dont think it fixes the probelm STILL! But all in all, Driver and Rancheros service is the same, just a BUTT load cheaper!

Nice find guys!
 

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Discussion Starter #8
is this problem only on the SX models? Mine had that problem at first on the 450xc, but as soon as we put the JD jet kit in, it runs perfectly.

My 525XC had the same bad bog problem at first hit of the throttle, and we fixed it the same way listed above except I increased the hole in the AP squirter to 18 thousands, if yours is running good just leave it, if later you add more mods and you get the bog, just follow the above directions or PM me
 

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I cant remember the number, but its the 2006+ if I remember correctly. Its was posted in one of these jetting threads. I know driver and ranchero know it
 

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After very extensive dyno testing on the KTM SX ATV, we developed a way to ELIMINATE the dreadful bog that we all have experienced on our machines. We are actively working on the XC, and should have information out on it shortly

WARNING:

USE THIS INFORMATION AT YOUR OWN RISK; WE AREN'T RESPONSIBLE FOR ERRORS IF YOU DECIDE TO PERFORM THESE MODIFICATIONS YOURSELF. THIS INFORMATION IS SOLELY PROVIDED AS A GUIDE. PROCEED WITH EXTREME CAUTION!!!

#1 Leak Jet Installation

To address the lack of adjustability of the accelerator pump we drilled & tapped the bowl for a leak jet. The leak jet allows us to address how far & long the accelerator pump squirts. We found that a #40 leak jet performed the best.

#2 Increase Accelerator Pump Squirt Nozzle Diameter

The next modification we made was to drill the accelerator pump squirt nozzle larger. From the factory the accelerator pump nozzle has a 0.013" opening. We found that by carefully drilling it to 0.016" (approximately 23% larger) it helped make the accelerator pump easier to tune and much more effective.

#3 Replace OEM Pilot Jet

From the factory the #42 pilot jet is too small. To fix this we simply replaced it with a #45 pilot jet. This corrected the minor idling issues especially when the engine is cold. This is very simple and easy to do.

#4 Replace OEM Needle

The factory needle's taper is too narrow at the tip which creates a lean issue from 3/4 throttle to wide open throttle (WOT) as well as the incorrect main jet being used. To cure this we replaced the needle with a needle found in the Honda HRC kit; it allowed us then to install the correct main jet.

#5 Install O-ring

Add the O-ring mod to the accelerator pump. The O-Ring size/number is 010

Drilling the leak jet & squirt nozzle are NOT recommended unless you have experience in dealing with 0.001" tolerances. Not to mention the drill bits are typically special order items.

If you send us the entire carb, we charge 0 to drill/tap the bowl for a leak jet & drill the squirt nozzle (return domestic shipping included). Active subscribing (paid) members to KTMATVHQ.com only pay ! (Parts included),

I am in the process of getting some bowls & squirt nozzles ready to go so I can offer them as a "kit" with or without a core charge. Unfortunately, I don't have any kit pricing available right now.



Fast64Ranchero & Driver311[/quote]


how long would it take for me to get my carb back after u recieve it??????
 

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Discussion Starter #12
how long would it take for me to get my carb back after u recieve it??????
I can do the work in one day if you really need it back, If I was to get it in the mail today, I would do the work tonight and send it back tomorrow, if you want it overnight I can do that but the cost is all on you and not cheap, figure $45 two day and $16-18 for three day, need to let me know in advance as I am out of HRC needles right now, I need to order more kits.
 

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ok, so got all carb mods done (apart from hrc needle).

runs really well but still not quite right.

still got a bog (5th gear jumps can be quite scarry and dangerous)

when in the garage, i take the air filter and rubber housing off.

if i wick the throttle open, i get fuel coming back out of carb and the bike bogging, or stalling if i keep it open.

is this normal if you go zero to full throttle straight away.

i have fuel screw 1 1/4 turns out, 45 pilot, 175 main 40 leak, ap squirter 0.016" blue needle 3rd clip.

i'm pretty sure its a rich bog but i don't know why.

i've got a hrc needle on the way but don't think this will cure it.

i'm wondering if something has happened with all the dismantelling and rebuilding of the carb in the last month or so.

any input would be great.

thanks
 

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I bet the hrc needle will fix things. Put it in and then drop your main to 165-168.
 

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^^^^exactely, most are running such huge main jets that they don't even realize they are leaving 5 WHP on the table just because of their jetting.
 

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now that i have my 450xc, i can tell its definitely running very rich, not like unrideable rich, but rich nonetheless.
 

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My sx stock took a 165mj to get close. right now with hrc needle and fastranchero mods Im running 162mj.
 

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Discussion Starter #18
+1 for Driver and Deadman, 165-168 main jet HRC needle on the 3rd clip from top, and go to 1 1/2 to 1 3/4 on the screw. are you using a 45 pilot? 55 leak jet? should be close
 

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+1 for Driver and Deadman, 165-168 main jet HRC needle on the 3rd clip from top, and go to 1 1/2 to 1 3/4 on the screw. are you using a 55 pilot? should be close

I think you meant 45 waltburger! :blink:
 

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When I say many are overly rich, I am referring to the XC's, just because I see what they are jetting at, and I know where my 525 needs to be with my A/F meter! Bigger mains only mean less power in most cases, unless you have big mods that require more fuel. (not just Intake, exhaust, etc)
 
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