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Hey guys need some advice here.
I have a '22 KTM 250SXF. I'm a slow MX racer - typically mid pack in the 60+ Vet Novice class in the SoCal OTMX club. Usual track for me is Glen Helen. I'm about 225lbs in shorts/T-shirt, so I'm guessing about 250 in full gear.
I have the rear set up pretty well - 5.4 spring set to 105mm sag with about 7mm of preload on the spring.
For the forks, I have the JBI DIY kit installed, which consists of a sub valve and a new leaf-spring type mid valve - similar to SSS KYB/A-Kit forks.
My issue is I'm not getting anywhere near full travel, and the forks feel quite harsh when landing from a jump, and very busy in braking bumps going into corners. I don't have a lot of confidence in the corners - it feels like I have a lack of front tire traction.
I checked my travel using the o-rings on my forks, and was several inches from bottoming. Granted at my skill level and age I'm not airing-out jumps - I'll usually land about 1/2 to 3/4 of the way over a table top. But even that feels quite harsh on landing. I was initially running about 145-148 psi in the fork. I lowered it down to 138 last sunday, but even at that I'm still at 3" from full travel. This already seems like too low of a pressure given my weight.
MXA says to keep lowering air pressure until I have about 1 to 1 1/2" of travel left, but I'm hesitant to keep going lower - won't that cause my forks to ride too low in the stroke, which in itself will cause harshness? I t seems I'd have to go down to about 120 or so psi to get another 1 1/2" - 2" of travel - and that just seems way too low. They say to do this before messing with the clickers though. (I'm at 12 out on compression currently)
The person that installed my fork kit did fill my outer fork legs with 280cc of oil in each leg. Manual states 230cc is standard, (+10/-50). Could this be part of the issue? Should I try draining 50cc out and see what happens? I'm also confused about whether to drain oil from both legs, or just the dampening side - I see both ways mentioned.
Thanks for your help
I have a '22 KTM 250SXF. I'm a slow MX racer - typically mid pack in the 60+ Vet Novice class in the SoCal OTMX club. Usual track for me is Glen Helen. I'm about 225lbs in shorts/T-shirt, so I'm guessing about 250 in full gear.
I have the rear set up pretty well - 5.4 spring set to 105mm sag with about 7mm of preload on the spring.
For the forks, I have the JBI DIY kit installed, which consists of a sub valve and a new leaf-spring type mid valve - similar to SSS KYB/A-Kit forks.
My issue is I'm not getting anywhere near full travel, and the forks feel quite harsh when landing from a jump, and very busy in braking bumps going into corners. I don't have a lot of confidence in the corners - it feels like I have a lack of front tire traction.
I checked my travel using the o-rings on my forks, and was several inches from bottoming. Granted at my skill level and age I'm not airing-out jumps - I'll usually land about 1/2 to 3/4 of the way over a table top. But even that feels quite harsh on landing. I was initially running about 145-148 psi in the fork. I lowered it down to 138 last sunday, but even at that I'm still at 3" from full travel. This already seems like too low of a pressure given my weight.
MXA says to keep lowering air pressure until I have about 1 to 1 1/2" of travel left, but I'm hesitant to keep going lower - won't that cause my forks to ride too low in the stroke, which in itself will cause harshness? I t seems I'd have to go down to about 120 or so psi to get another 1 1/2" - 2" of travel - and that just seems way too low. They say to do this before messing with the clickers though. (I'm at 12 out on compression currently)
The person that installed my fork kit did fill my outer fork legs with 280cc of oil in each leg. Manual states 230cc is standard, (+10/-50). Could this be part of the issue? Should I try draining 50cc out and see what happens? I'm also confused about whether to drain oil from both legs, or just the dampening side - I see both ways mentioned.
Thanks for your help
Not having any knowledge of the JBI settings, at 225lbs, I personally would recommend you run much higher psi around 168-170 +/- and also set your oil volume at the lower range around 180cc in both legs.
That confirms what I was thinking - that there is just too much oil in the forks. The JBI website does state you can run a little less air than usual. For my weight I would think 168-170 would be typical like you mentioned. Maybe with the JBI kit I could be down in the 150s somewhere- IF I lower the oil volume like you suggest. And you did say both legs, so thanks for clearing that up for me.
I think I might just drain all the oil from the forks and just add the 180cc myself so I know for sure the exact volume I’m starting with.
Appreciate your help Slipdog!
We are the same weight and I run 157-160 in my stock 22 AER’s.
The Shop
Also, not sure how many hours you have but these forks noticeably free up at 5, 10, and then 15 hours. I've also found that being very careful to get a good bleed on the damping cartridge helps the plushness.
What do you think about the air coming out of my left bleeder? It was a good 2-3 second hiss. Bad seal head? If so I might do the SKF glide kit, or just take the $200 I’d spend for that and put it towards a Raven kit
Also, over the years I've learned that going too far from stock, it's easy to get lost... I like JB and I've bought stuff from him over the years. That said, that stock 2022 midvalve is a great design and I was able to achieve what I think you are looking for by just a couple of small adjustments on the mid valve and trampoline springs.
Either way, just do what makes you happy, and if that means a new set of cones, then go for it.
My 17 FC350 (your old bike, swatdoc) could never seem to make the forks work right. Revalved the stock setup, went to Gold Valves, even tried Ohlins TTX-22 inserts. Until I ponied up for Blackjack inserts it always had harsh slap down along with less than stellar small bump absorption.
How's the 350 running?
Pit Row
Just a thought, since it's really easy to add oil to the forks, maybe drop the level way down to 180cc, and just add 10cc's at a time at the track and record what the findings are.
The 350 is a monster. I put the stock clutch back in, swapped the GET ECU for the stock one, tuned by Twisted Development, and I run it on pump gas. Certainly not as fast as it was before, but I still fear no 450 once the revs come up. If I don't holeshot, it's not the bike's fault. I was really looking forward to racing Mammoth on it (that's the specific reason I bought the 350), but caught covid a few days beforehand and killed that vacation.
I did recently tighten up the sag from 102 to 97.5, the result was tighter steering, but it also helped settle both the front and rear end, which was a bit of an unexpected surprise. Once you get your forks feeling good, that might be another avenue to check.
I ask because my stock AER forks on my 450 recently started doing the same thing. I was having to add air between motos and bleed the outer chamber of the air fork. It ended up being the “seal head” for me.
However, this is with the bike just sitting in my garage. I’m still a little leery, because why doesn’t the right side fork ever do this????? Only the air side.
Is it possible the air chamber seal head only leaks when the bike is being ridden and the pressure ramp up?????
I’ll know next time I ride. If it does it again I think the seal head is an issue like on your bike. If so I’ll either get the kit from SKF, or just put that $200 towards a Raven or Blackjack spring kit
I was hoping you had it resolved because I’m real interested in the JBI set up for my AER’s and was looking forward to a review.
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