Latest Jetting Opinions: 540, HRC, 41mm, KTMBill, 806
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  1. #1
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    Latest Jetting Opinions: 540, HRC, 41mm, KTMBill, 806

    If this info is buried in a thread please advise, been surfing threads all afternoon and haven't found a close enough one! I'm looking for further jetting advice at any given altitude & temp(I can back calculate air density from there), for a 525xc with 540 12.5:1 kit, trail porting, +1 intake valves & deshrouded, 41mm carb + HRC needle & emulsion tube (all the ranchero mods), 806cam, KTMBill exhaust.

    I'm around sea level - 1000ft, and typically 70F temps, and I believe I'm still rich at a 160main, 40 pilot, screw at 1.5 turns, and HRC needle at 3rd clip. It runs like a raped ape, but my gut says a 158 main and 38 pilot should be about right, but I don't want to burn her up! Piston and plug are pretty clean, a bit of soot on the tip of the porcelain, no aluminum bits, and a touch of soot at the tail pipe. Thoughts please!? And I don't have local access to a dyno, looking for similar modifications - advisement. Thank you!!!
    Last edited by hiperfind; 11-13-2014 at 01:17 AM.
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.

  2. #2
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    i think you are about spot on there, most id do is try the 158, think thats what im running.

  3. #3
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    Well you already know what I am running a 38 pilot seems perfect no choke needed until below 55 but when it was 30 out the 38 pilot is to small so 40 maybe for extreme colds? Didnt try yet... I am at a 158 main for 60-80 temps but ran the 158 in 35
    degrees and unleashed more power no popping or anything and it left some black soot ob my 6 pack rack so thinking a 156 is my next step for this cold weather and trying a 154 for warmer just to see. I am at around 800' above sea level have same mods as you minus plus 1 valves and a 41.5mm carb oh and a fci intake
    Last edited by racingricks87; 11-13-2014 at 05:47 PM.
    2008 Ktm thumper 540 12.5:1, thumper trail port, kw valves, 806 cam, carillo rod w/ welded crank pin, mino hf pump, 41.5 mm carb with hrc needle, drilled squirter to .020", 160 main, 40 pilot, 45 leak jet, emulsion tube, beadlocks, ac nerf bars, elka steering stabalizer, ignition curve switch, bills pipe, fci intake, thumper crankcase breather, steering stem bearing mod, frame scuff guards, (6 pack rack, A arm, swing arm, frame body guards) from prm, 15t sprocket

    2000 Lt80
    2000 Rancher 4wd

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  5. #4
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    Sticko2 Thank you! Sounds like we have a very similar build? Do you have any elevation or temperature-based jetting changes you can share as well? I can estimate via air density, but I'm curious what other experienced riders have been successfully jetting to across higher elevations & large temp changes
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.

  6. #5
    Senior Member KTMATVHQ Member
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    Thanks Ricky, appreciate the recap! Have you tried 2 to 2.5 turns out on the fuel screw instead of changing to the 40 pilot? Might be the solution there...
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.

  7. #6
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    Yea I didnt mess with it. Think i am at 1 3/4 turns out now
    2008 Ktm thumper 540 12.5:1, thumper trail port, kw valves, 806 cam, carillo rod w/ welded crank pin, mino hf pump, 41.5 mm carb with hrc needle, drilled squirter to .020", 160 main, 40 pilot, 45 leak jet, emulsion tube, beadlocks, ac nerf bars, elka steering stabalizer, ignition curve switch, bills pipe, fci intake, thumper crankcase breather, steering stem bearing mod, frame scuff guards, (6 pack rack, A arm, swing arm, frame body guards) from prm, 15t sprocket

    2000 Lt80
    2000 Rancher 4wd

  8. #7
    Senior Member KTMATVHQ Guru
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    To the guys that are going to the smaller pilot jets: are you dropping down so low to get better throttle response? Have you done any accelerator pump work? 38 seems really low to me. I think I still have a 42 or 45 in my 525 at 2500 feet. We have pretty dry air here in Montana though. Also, I guess it's possible that the extra airflow from the porting and big bore is pulling more air through the carb and thus more fuel with it?
    Mine:
    2017 Husky FX 450
    2009 505 SX
    2008 525 XC-modded for mx (currently 450 cylinder)
    Dad's:
    2009 450 SX
    2008 540 XC

  9. #8
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    Actually, I've spent more time tuning my AP and getting the right nozzle stream(s) and such than I have riding the damn thing! The effort is to obtain the best throttle response and best powerband across the board - without going too lean. You're right about the air volume; the combination of compression, bore, porting, pipe, larger carburetor diameter, larger intake valves, increased lift and duration on the cam, and any intake mods will move more air, creating a greater venturi effect over the jets, sucking more fuel from the same jet diameter.
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.

  10. #9
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    Hello Fellas! I going to chime in here as a newb. The FCR carb and the possible mods are new for me, so forgive me if I state incorrect info or have misunderstood items. I've been perusing the forums, thumpertalk, KTM FB page, etc. and will be asking Travis' opinion. I'm in the middle of my winter rebuild and was considering carb mods. Also, since Ranchero is no longer doing mods where is everyone going for carb mods?

    Here's what I've got:
    540 w/ 12.5:1 CP piston
    KTM Bill exhaust
    Slide Jet: OBEKR 3rd slot from top
    Main: 182
    Pilot: 42
    Cold Start: 85
    Fuel Mixture Screw: 2 turns
    Pilot Air Jet: 100
    Leak Jet: size? (having problem getting it out)
    Stock AP diaphragm

    Here's what I'm considering:
    Slide Jet: HRC Jet, 3rd slot from top
    Main: 158/160
    Pilot: 42
    Cold Start: 85
    Fuel Mixture Screw: 1.5 - 2 turns
    Pilot Air Jet: 100
    Leak Jet: 42/45
    Thumper Emulsion tube and dual spray accelerator pump kit
    Thumper to bore out carb to 41 mm

    KTMBill is putting an O2 bung in my exhaust, so I'll be tuning with an A/F meter for its different ranges. So let me know your thoughts on what I've missed. Also, why does KTM not want you to take out the forbidden screws so you can change to a dual squirter?

    Cheers & Thanks for the help!

    Julia

  11. #10
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    Hi Julia, and welcome! Youre pretty much on the right track with the jetting Suggestion at sea level and 70 ish temps, although without porting and/or larger valves you could be lean by 1-2 sizes in the main and pilot. If you have the gear to support the a/f ratio data and what to change with the info, then your jetting should end up even more spot on than most riders on here. Regardng the squirter, I too fought the same logic. After seeing the guts over and over, its no big deal. My guess is Keihin has some policy internally that they discourage heavy modifications. I ended up drilling out a single hole to .018" and it works great...I personally could never get the dual squirt to shoot high enough to hit the valve area and hence the bog remained. Good luck!
    Last edited by hiperfind; 12-29-2014 at 02:31 AM.
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.

  12. #11
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    Yes it seems to be most people I have talked with cannot get the dual squirt to work properly it just adds a bog. Drilling stock squirter out is much cheaper and works wonders. Bought a small hand drill bit kit off amazon for like $10 it takes time and patients but you can drill the hole by leaving the squirter right in the carb .018-.020 is where u want the hole to be at
    2008 Ktm thumper 540 12.5:1, thumper trail port, kw valves, 806 cam, carillo rod w/ welded crank pin, mino hf pump, 41.5 mm carb with hrc needle, drilled squirter to .020", 160 main, 40 pilot, 45 leak jet, emulsion tube, beadlocks, ac nerf bars, elka steering stabalizer, ignition curve switch, bills pipe, fci intake, thumper crankcase breather, steering stem bearing mod, frame scuff guards, (6 pack rack, A arm, swing arm, frame body guards) from prm, 15t sprocket

    2000 Lt80
    2000 Rancher 4wd

  13. #12
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    Thanks for the input fellas. Wonder why the dual squirter is such an issue. Are the holes in the dual squinter the same size as the single? I also have a few questools about adjusting the duration of the spray and what folKS like to use to adjust the diaphragm.

    Cheers!

    Julia

  14. #13
    Senior Member KTMATVHQ Guru
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    Before I had the Ranchero mods done, I was using a AP diaphragm out of a CRF 450 dirt bike. Little trick the bike guys from ktmtalk.com used. The stop is longer on it so it shortened the duration of the squirt. Not quite as good as drilling the nozzle and installing a leak jet in the fuel bowl, but it is cheap and does help some if you are not comfortable doing the full carb mods.
    Mine:
    2017 Husky FX 450
    2009 505 SX
    2008 525 XC-modded for mx (currently 450 cylinder)
    Dad's:
    2009 450 SX
    2008 540 XC

  15. #14
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    Below are some links that I found interesting. Some are not quite a perfect fit to the application, but still interesting.

    http://www.keihin-na.com/assets/1/7/slide_valve.pdf

    ThumperFaq: FCR Jetting

    ThumperFaq: Tuning the AP

    Cheers!

    Julia

  16. #15
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    Installing a leak jet is what will adjust spray duration. Bigger the leak jet the less duration. On the squirter yes the holes are much smaller i think maybe to small. Plus getting the streams of fuel to shoot perfectly into the intake is a chore.
    2008 Ktm thumper 540 12.5:1, thumper trail port, kw valves, 806 cam, carillo rod w/ welded crank pin, mino hf pump, 41.5 mm carb with hrc needle, drilled squirter to .020", 160 main, 40 pilot, 45 leak jet, emulsion tube, beadlocks, ac nerf bars, elka steering stabalizer, ignition curve switch, bills pipe, fci intake, thumper crankcase breather, steering stem bearing mod, frame scuff guards, (6 pack rack, A arm, swing arm, frame body guards) from prm, 15t sprocket

    2000 Lt80
    2000 Rancher 4wd

  17. #16
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    I wanted to add my $0.02 to this thread. I am 3 hours on my 540 rebuild and this is what I found was needed while tuning the carb with my A/F ratio meter and Trail Tech temperature sensor. Thumper suggested I run the carb 12.8 to 13.1 while under load for the three circuits of pilot, needle and main. So, I have my thumb throttle marked for each of these circuits to I know where my slide is at for each circuit while riding. I strive to get closer to 14.7 while at idle, but my ratios like to stabilize in the 180 temps. Anything in the lower temps is a bit leaner, which would be expected and my idle is set to 1800 rpm.

    Here's what I've got:
    540 w/ 12.5:1 CP piston\
    Carillo Rod
    833 Cam
    KTM Bill exhaust with O2 bung for A/F ratio meter
    Carb is bored out to 41 mm by Thumper
    Idle Mixture Screw: 3 turns
    Idle Fuel Jet: 85
    Pilot Fuel Jet: 40
    Pilot Air Jet: 100
    Jet Needle: HRC NGPR 4th slot from top
    Needle Jet: Thumper Emulsifier
    Main Jet: 160
    Leak Jet: 42
    Squirter: Dual Squirter from Thumper
    Stock Accelerator Pump diaphragm

    I need another two hours before I am fully broke in so there might be some more adjustments, but I extremely pleased so far. The power is full of torque and rolls on butter smooth anywhere in the rpm curve without the dreaded bog.

    Cheers!

    Julia Aebersold

  18. #17
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    Thank you very much for the info Julia! Can you elaborate on your temp.and elevation while tuning, and does your head have porting and oversize valves from thumper as well?
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.

  19. #18
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    This is the best tuning information I have ever seen with regards to tuning FCR Carbs
    carbkie.html, Keihin FCR Carb Tuning Procedures
    My Bikes:The Beast: Raptor660727cc (105mm piston 14.5:1 CR)3 plug HV ported headDual Kehin FCR39 carbsCustom made full dual exhaustThe Beauty: KTM450XC554 (99mm bore) with Cut7 cam & 43mm carbSX A-Arms & Yamaha Front rimsDual rate rear springs (Thanks Kiwicraig)Rear Spacers to adapt to Yamaha stud patternMods to come:Suspension nextThe SledgehammerSuzuki TL1000SOhlins rear/Racetech kitted forks

  20. #19
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    Julia,
    Just reread your.post, watch out for your ide.screw after 2 turns out...they like.to fall out! If you are seeing the need to go there, change to a 42 pilot. Still curious about your head mods, and elevation and temp... Thanks!
    2008 525xc; exhaust & skid by KTMBill, suspension by RocketRonRacing, Thumper Racing 540 12.5:1 kit + trail porting +1 KW valves, breather, carb emulsion tube, Mino hi-flow water pump, 806 cam, 41mm carb w ranchero mods by Dave Hopkins, GDC intake mods, Rox Risers, Precision Stablizer, SX stem bearing, PRM arm skids, and the wisdom on KTMATVHQ! Jetting above 25C: below 5000 ft: 162main, 42pilot, 1-1/2 turns out. Above 5000 ft: 155main, 42pilot, 1/2 turn out. Below 25C-up one on main.


 

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