First KTM some questions for you all...
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  1. #1
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    First KTM some questions for you all...

    Hi all,

    Iíve been learning a lot from this site over the past few weeks since I picked up my first ktm. As stated Iíve been reading everything I can prior to making the decision to sign up. I know itís a little quiet around here but this seems to be the most focused and genuinely helpful forum Iíve explored.

    I just picked up a 08 450xc a month or so ago and immediately tore it down for a full rebuild. The head and carb went to john at racers edge for some work. The factory 540 that was on it looked great and had relatively low hours but I sent it to millennium for new nikasil for a fresh start. Bottom end looks great and everything is within spec and has about 40 hours on it.

    My first question is in regards to a piston for my set up. Iím looking to run high compression for an Rfs. I understand these motors last a long time compared to a yfz or trx and some of that has to do with the lower compression they run. Iím not to worried about getting 100 hours out of a motor. I donít ride often and would be able to get a few years out of a higher compression bike. Simply, based on me riding it 3-8 times a year. Plus I like wrenching on my bikes almost more than riding them.
    Anyways, All I can find is 12.5:1 pistons and that seems pretty lame for race gas numbers. John is decking the head slightly to bring me up half a point. But Iím looking to be 13.5-14:1 comp.
    is there any 97mm piston options out there that will put up the numbers Iím looking for? Or even 13:1?


    Second question is in regards to the carb. I bored the ap nozzle to .019 did the 0ring mod and tapped for a leakjet install. Itís a 43.5mm bore with hrc needle etc.
    my question is what is this emulsion tube I see guys running from Travis do? Is it necessary/beneficial?

    And lastly, the bike came with the standard hmf not the comp version. Iím really thinking about pulling the trigger on one of ktm bills pipes. Would I see a substantial gain. Or should I save the cash and just repowder/ ceramic coat the hmf?

    Iím really shooting for low 60s while using a factory 540. Just wondering if there is a substantial but dyno diff between the two pipes with relatively built motor.

    Iíve had a few built 450s over the years and the engineering on the Xc is pretty incredible for a production atv. I was amazed taking this thing apart.

    Thanks


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  2. #2
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    My 540 surpassed 60 ponies with ease. Your only option to go more compression is having 4 of them custom made, about 1000 bucks. Speaking of that, hold off on them plating your cylinder until you can send them a piston to specifically size it to your cylinder!
    My KTM bill pipe showed a 2-4 HP increase over the hmf. Bill builds ones specifically for the 540s to breathe. Best bet would be an akro pipe but good luck finding one of those. I think one was for sale on Facebook the other day, there’s a KTM group and that’s where all the traffic went. The biggest power maker is the head setup. Good port job with +1 intakes and a multi angle valve job. I was fixing to deck my cylinder head but I was already about 60/80 thou with the cp 12.5:1 which is as close as these guys need to be getting. Your cam will matter big time too, 43.5 is a lot for a 540 and you’ll likely see bottom end loss, but an increase up top. Not really good for the XC engines, they like to spread the cranks at high rpms. If your pin isn’t welded and your axial clearance on the crank isn’t set to about .019 thousandths I recommend doing that, it’s almost a must. Your cane choice will come to be an 8/06 or an 8/33. I usually say the 8/33 is better but since your carb is so big you might want to compensate a little with the 8/06. Or maybe tell raceres edge your dilemma and have him go a little smaller on the porting to compensate. It’s all about finish that amount of air brought in that makes it happy. I also recommend a cooling mod with a bigger/high comp setup (NOT THE Y KIT!), a high flow water pump, and some gym time, cuz you’ll be holding on.
    If the “o-ring” mod you’re referring is the o-ring on the accelerator pump arm, you wasted your time. Doesent do much.
    The imulsion tube helps a little. It mainly helps at low RPMs to help get the fuel to a vapor. In theory helps get rid of bog, and since all the fuel is vaporized it can all burn, so better/cleaner burn, as well as efficiency.
    Big reason stock engines with FCRs develop a bog is the leak jet is just way too rich. That’s why the adjustable ones work. I think the 540 is a little too big to benefit from those. Trying a current gen AP straight from Keihin this time around with some other things, we’ll see how it goes.
    Last edited by Youngwildandfree; 02-20-2020 at 05:45 AM.

  3. #3
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    You mind sharing what the Facebook group is called? I’d love to be apart of that. Nobody is ever on here except for like 3 dudes.

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  5. #4
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    Quote Originally Posted by Youngwildandfree View Post
    My 540 surpassed 60 ponies with ease. Your only option to go more compression is having 4 of them custom made, about 1000 bucks. Speaking of that, hold off on them plating your cylinder until you can send them a piston to specifically size it to your cylinder!
    My KTM bill pipe showed a 2-4 HP increase over the hmf. Bill builds ones specifically for the 540s to breathe. Best bet would be an akro pipe but good luck finding one of those. I think one was for sale on Facebook the other day, thereís a KTM group and thatís where all the traffic went. The biggest power maker is the head setup. Good port job with +1 intakes and a multi angle valve job. I was fixing to deck my cylinder head but I was already about 60/80 thou with the cp 12.5:1 which is as close as these guys need to be getting. Your cam will matter big time too, 43.5 is a lot for a 540 and youíll likely see bottom end loss, but an increase up top. Not really good for the XC engines, they like to spread the cranks at high rpms. If your pin isnít welded and your axial clearance on the crank isnít set to about .019 thousandths I recommend doing that, itís almost a must. Your cane choice will come to be an 8/06 or an 8/33. I usually say the 8/33 is better but since your carb is so big you might want to compensate a little with the 8/06. Or maybe tell raceres edge your dilemma and have him go a little smaller on the porting to compensate. Itís all about finish that amount of air brought in that makes it happy. I also recommend a cooling mod with a bigger/high comp setup (NOT THE Y KIT!), a high flow water pump, and some gym time, cuz youíll be holding on.
    If the ďo-ringĒ mod youíre referring is the o-ring on the accelerator pump arm, you wasted your time. Doesent do much.
    The imulsion tube helps a little. It mainly helps at low RPMs to help get the fuel to a vapor. In theory helps get rid of bog, and since all the fuel is vaporized it can all burn, so better/cleaner burn, as well as efficiency.
    Big reason stock engines with FCRs develop a bog is the leak jet is just way too rich. Thatís why the adjustable ones work. I think the 540 is a little too big to benefit from those. Trying a current gen AP straight from Keihin this time around with some other things, weíll see how it goes.
    Thanks for the input. Much appreciated. The crank was welded by the previous owner when he installed the 540. I have receipts to match.

    As far as the piston I did purchase a cp 12.5:1 and move forward since I couldnít find anything else. millennium already has it. I was just looking to see If I had another option. Plus if I did commit to another piston with a proper hone and setting ring gap, I would think it wouldnít be a major issue.

    The o ring mod is the exact same as the Yamaha zip tie mod and wasnít any trouble if you think itís going to hurt Iíll surely remove it.

    Full build specs are as follows. RE porting. Plus one valves. All new guides, seals etc. 5 angle cut with new seats. 12.5/1 cp. 43.5 carb bore with the small mods listed on this site to help with throttle response and off idle bog. I have an 833 and a web 821 to try and see what I like best im sure there both pretty similar. I mostly ride old coal access roads and big coal hill shoots. Iím not at all worried about some bottom end loss. I mostly ride my super serval so Iím used to a bike making power between 6 and 12k. Iíll order a oversized impeller set up from Travis to help keep the temps down. Iíll look into that akro on Facebook if itís not sold already. If so Iíll reach out to bill.

    Iíve had two people tell me the 43.5 is to big for this motor which is confusing to me. Ive ran a 42.5 on all my 450/480 build with great success. I would think the 540 would benefit greatly with anything over 44. Itís a lot of motor to feed. I understand xc guys wanting to keep the low end this stay with the smaller carbs. But to truly use the full potential of that kind of displacement I would think the bigger the better. Most of the big duner Honda builds canít exceed 66hp with an fcr and move on to something bigger.

    Am I missing something? Do these motors operate differently?


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  6. #5
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    Yeah, there is not much going on here and its kinda a bummer. This has been by far the best ATV forum that I have been a part of. YWaF has really stepped up to fill the gap that was left when a lot of the Senior members with solid technical knowledge dropped off. So props to him for trying to keep the heartbeat pumping around here.

    Quad97 is another member that still posts every now and then and really knows these bikes and provides outstanding information and has been here since the beginning.

    Your builds sounds like it’s going to be a blast. Props to you for going with John at RE. He is one of the best in the business. I think he is slowly starting to dive into the KTM’s a bit. Last time I was over there he had 1 in the shop that he was doing a build on. Did he have any recommendations for pistons? Off the top of my head, I would think CP or Diamond might do something with 13.5 compression or more. I run a 13.5/1 Diamond in my Raptor but the stock piston in my KTM.

    I can’t really give you much technical info on the Carb as I haven’t really messed with mine beyond an R&D float bowl and the O’ring mod. I have a friend that his bored to a 41mm with the Ranchero Mods but he can’t seem to get the jetting correct.

    As far as the exhaust goes, I would say go with Bills pipe. It’s badass and very loud! He builds a big core header that is very nice!! His can is fine but imo could use a cooler/meaner tip on it and shortened it up a bit.

    Welcome here brother. Threads like yours help keep this place going. I’m probably 1 of the 3 dudes left here that still posts that was referred to lol and it’s cause the KTM quads were the best sport quads ever made and I absolutely love mine as much as I did when I bought it off the showroom floor.

    My only other real advice is don’t go too big on these (RFS) Motors. A 540 in the low to mid 60’s is a solid build with a good combo of horsepower and reliability.
    Last edited by steveo525; 02-20-2020 at 03:48 PM.

  7. #6
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    I appreciate you sticking around and helping too, I don’t want to see these die. Been doing as much die-off control as I can.
    So your Honda vs ktm comparison is apples to oranges. Heads flow different, different motor Configurations, intakes flow different, etc. I can go into depth if you’d like.
    Go for the thumper tube.... why not? Ya know?
    It’s not so much that either the 43.5 or the 8/33 is bad in itself, it’s more of them combining WITH porting is just too much air and starts making power all in one spot, the top. You don’t need +1 exhausts, just intakes. It’s mainly to fix the weird and soft intake valves from stock. You’re kinda trying to beat Honda at their own game by doing that and going for straight ponies instead of taking advantage of the torque the RFS motors make, that’s where they shine. You can make 60-65HP on a Honda or yamaha (not reliably, but still), you can’t really make that number and get 40-45 ft lbs on torque unless you go way up in horsepower, too. And then you’re really unreliable.
    Steveo is right, anything passed this build may start to get unrealible. Anything more than mid 60s on an rfs gets sketchy.
    It’s probly not a huge deal but Getting the plater/homer the piston insures perfect Piston to wall clearance. You could have Travis mic it and send the plater the perfect measurement. It’s not so much of a big deal, but a clylunder that is just a tiny bit big for the piston will allow the piston the slap around more and hurt things from the longevity standpoint. That’s why pistons that don’t come with cylinders say right in the directions how crucial it is to measure piston to cylinder.
    You aren’t hurting anything with the o-ring mod, but snap the throttle and watch it vs when it’s on and off, the o-ring streaches and does nothing, it also Messes with your AP timing.

  8. #7
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    Thanks for all the info guys and Iím glad a few of you all stuck around. Certainly makes my life easier since Iím new to these motors/bikes.

    I found a used akro online thats is pretty good shape. Itís 1000 for a used complete pipe. All4 is half thats price. Is there any benefit other than fit and finish between the two?

    Iím not really trying to go any bigger than I am. The bike came with the 540 so I figured I would replate and work with what I have. If my curve moves to far to the right, Iím hoping to make the adjustments needed with different cams. I do ride mostly 3-5th gear so Iím confident John has me in the right direction.

    I did call and talk to Travis for a while prior to deciding on john and honestly the deciding factor was customer service. I know john does great work even if ktms arenít his specialty. However, every question I have, every phone call I make, he personally picks up or calls me back with 30 min. Itís pretty impressive and rare in the atv industry.

    Travis was pushing me to do a 570 with massive valves. Not where i wanted to go with the motor or the bank account. Iíve also heard a few issues with his work. Not often but it seems when the issues do arise. They are catastrophic.

    One last question is the OEM clutch. Iíll be replacing it with new OEM fibers and plate. The basket has no grooves whatsoever. Will the OEM clutch in top condition hold 60-65hp? Do people put lockupís on these bikes? Not a fan of them and avoid them at all costs. Iíd rather replace a clutch every season than run a lockup.


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  9. #8
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    Thumper used to be like that, I could give Travis a ring whenever. Now its days of waiting for replies. I think they just got so busy they don’t even know what to do, they are good people in my experience. I like pushing my business to him because he makes the billet cranks and other stuff for the rfs engines. I’ve heard nothing but great things about racers edge, I would be more than confident with him. Keep in mind these motors are FAR different from the rest of the pack. I would mention to him the added axial clearance of the crank if he’s going into the bottom end. The stock clutch should hold just fine. These clutches are noisy but they are steel baskets and toughly made, worst case some Hugh pressure springs would do the trick. Doubt you’ll come to that. If you told Travis about the 8/07 cam, that’s why he was wanting you to do the massive 570. It matches the massive cam lol. If you ride in high gears and are going to get all this motor, highly recommend going up a tooth in the front and maybe even down one in the rear. My 540 basically needed the 8/33 cam and 15 front sprocket just to tame how “rip it from your arms” it was. Hard to hold on to for hours of nonstop hammering...

  10. #9
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    Quote Originally Posted by Username View Post
    You mind sharing what the Facebook group is called? I’d love to be apart of that. Nobody is ever on here except for like 3 dudes.
    Sorry just noticed this, the main group is ktm 450/525xc owners. There’s a “ktm quad parts 4 sale” a “ktm ATV worldwide” and a “ktm quad eruopa”.

  11. #10
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    Get Bills pipe. He has the Big core header. I would get it ceramic coated (that will cost more). I run the akro header and it’s a really nice fit and finish but performance wise on a built 540, Bills pipe is the way to go. My buddy runs it and imo it’s the best exhaust out there for the KTM’s.

  12. #11
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    Perfect. Thanks for the replies guys. Much appreciated. Iíll pull the trigger on a bills pipe after hearing your input. Doesnít seem like Iíll benefit much from the hefty Akro price tag.

    Do you guys have info on the ktm cams. Lift, duration etc. like I said I have a 833 in my hand and already ordered the web 821. But just in case I want to change the power delivery some, I would like to know whatís out there.

    Nothing against Travis at all. They seem like a great business and certainly have parts that you just canít get from anyone else. So, I think every ktm owner benefits greatly from what he has donít to this little niche community. And everyone needs something from him at some point.

    I donít race at all. Itís all rec riding. I just like my bikes to be borderline scary lol. I ride hard but not trying to impress anyone, just building something that puts a smile on my face. Honestly this is the first four stroke Iím very excited about. Every other high 50s 450 Iíve owned has left more to be desired and I always just sell them and go back to my banshees.

    Everything is all torn down now. Iím taking everything to powder today. When everything starts rolling in and I start assembly in a few weeks Iíll be sure to start a little build thread and would appreciate any input/criticism you all may offer.

    I just got a message from Klaus about another black and white fender run. Which changes everything in regards to colors for me now. But Iím thinking Iíll keep it clean and simple. I want it to look like an OEM bike. Kind of like a sleeper. So Iíll be going all black powder on everything.


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  13. #12
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    Should be a sweet build, WEB makes cams and thier charts are on the website. I’ve heard of maybe CT or fuel customs making custom cams, not sure about all that. Hot cams made one but it’s more like the 8/07.
    I had a chart for the factory cams but I don’t know where they went....

  14. #13
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    Quote Originally Posted by Youngwildandfree View Post
    Should be a sweet build, WEB makes cams and thier charts are on the website. Iíve heard of maybe CT or fuel customs making custom cams, not sure about all that. Hot cams made one but itís more like the 8/07.
    I had a chart for the factory cams but I donít know where they went....
    Gotcha. Yea I was just curious for the factory cam cards


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  15. #14
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    I don't have a lot of experience to add here other than having my 570 built about a year ago. Travis at Thumper offered to build mine with a 13.5:1 piston. I don't know what brand it was because I wasn't interested in that much compression, but it is available. Also he told me he would not recommend the emulsion tube on a atv, saying its mainly for bikes. I know everyone has their own experiences, but Travis didn't push for me to go big on anything with my build. Maybe its because I told him I wanted to make decent power at all rpm levels. I basically had my motor build completely at his suggestions which is a 41mm carb, Thumper stage 3 cam, +1 intake valves, trail ported head, and 12.5:1 compression.
    2009 525 xc Ohlins steering stabilizer, otherwise stock

  16. #15
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    Travis is the only person I've seen advertise higher compression setups than 12.5:1 on the bigger RFS bores. I believe he's using mostly CP pistons now. The bike side of things is probably booming for him right now with the popularity of snow bikes as they require every bit of power you can get. The popularity of KTM bikes has gone up in general in recent years compared to what it used to be too.

    The old man's factory 540 kitted machine is running a 43.5mm bored carb and I don't feel it's too much on that motor. With that much displacement the low end loss is not noticeable compared to my 41.5mm on my 525. His machine and my 525 setup are both running Akrapovic pipes, 806 KTM cams, opened up air boxes, and stock heads and valves. My 525 runs a 41.5mm carb with the Ranchero mods and HRC needle while his 43.5mm uses a JD needle and just the o-ring for AP mods. I run 13.0:1 compression in my 525. My 525 revs faster and is better suited for racing and track use. His 540 is a torque monster and will eat my lunch in the sand dunes where that torque can be put to use. It feels like his falls a little flat on top and I can see where it might benefit from larger valves, port work, and a bigger cam. However, it is the smoothest running modded engine I've ever been around and is not picky about it's jetting. We both feel like it's not worth the risk of wrecking its good nature with head work until it needs it at some point. And if you keep these engines lower in the rev range where they make their power and are happiest they will live longer.

    I admit I'm not on here as much as I used to be before the racing dried up in my area. Had to semi-convert to 2 wheels (out of necessity, not choice). Now I only ride the quads a couple times a year, but have no plans of getting rid of them anytime soon!
    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


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