Posts
989
Joined
4/1/2008
Location
Austin, TX
US
Hello, I've been away a while but decided to get my 2013 KTM 250 SX custom tuned by Derek Harris of Harris Performance in Central Texas this last week and get back on a dirt bike. I'm decent at jetting but had struggled a bit with this bike because I have a weird combo. I added a 300 cylinder to my 250SX. Then on top of that I stroked it 5mm for a total engine displacement of 314cc. I also wanted Derek to test my PV settings and ignition timing settings to verify I had tuned that for best overall performance.
I went thru 3 carbs on the bike some time back and settled on the Lectron and overall liked it greatly but I would have issues with slight pinging unless I ran the bike a bit rich and/ or with race fuel. It also didn't have much low end snap which I attributed to the port timing being all jacked up since I just added a spacer under my cylinder when I rigged up the stroker kit.
I dropped the bike off and Derek Harris dialed the jetting/ PV setting, and ignition setting on race gas. But he detected some low end leanness and after a call to Lectron they overnighted an updated needle profile directly to Derek. Those Lectron guys have a great product and excellent service btw.
With the new needle in hand Derek began testing again and found some more power pretty much everywhere. Down low and especially at the top He also had the bike running great on pump gas. I delivered the bike to him with race gas, which frankly I hate messing with so Derek went and bought some pump gas, mixed it up, and tested it himself in my bike. I'm really glad he did too! Of course I know I could pick up some low-mid if I went back to high compression and race gas but I don't want to mess with that any longer.
Below is the dyno results showing before and after hp & tq for my engine. Needless to say I'm very pleased and the price was beyond fair for what I got.
I'll also add that I've seen my dyno graph over-layed with several 450Fs powerbands and it holds it's own. Typical of a 2 stroke it's got less rpm to work with, but I will offset that with longer gearing to keep it in the high numbers longer. My days of riding my best are past me and I really want a long smooth powerband first and foremost. To sum up, my bike is notably stronger (7-8 rwhp) than a typical '09 CRF450. My bike peaks slightly above a '16 KX450F but has less overall power and tq. And a '16 SX450F pretty much whips my bike everywhere by 5hp/ 5tq, but then it does the same on all the other 450Fs.
I have not ridden the bike yet but should get some time on it this weekend and will report back.
I went thru 3 carbs on the bike some time back and settled on the Lectron and overall liked it greatly but I would have issues with slight pinging unless I ran the bike a bit rich and/ or with race fuel. It also didn't have much low end snap which I attributed to the port timing being all jacked up since I just added a spacer under my cylinder when I rigged up the stroker kit.
I dropped the bike off and Derek Harris dialed the jetting/ PV setting, and ignition setting on race gas. But he detected some low end leanness and after a call to Lectron they overnighted an updated needle profile directly to Derek. Those Lectron guys have a great product and excellent service btw.
With the new needle in hand Derek began testing again and found some more power pretty much everywhere. Down low and especially at the top He also had the bike running great on pump gas. I delivered the bike to him with race gas, which frankly I hate messing with so Derek went and bought some pump gas, mixed it up, and tested it himself in my bike. I'm really glad he did too! Of course I know I could pick up some low-mid if I went back to high compression and race gas but I don't want to mess with that any longer.
Below is the dyno results showing before and after hp & tq for my engine. Needless to say I'm very pleased and the price was beyond fair for what I got.
I'll also add that I've seen my dyno graph over-layed with several 450Fs powerbands and it holds it's own. Typical of a 2 stroke it's got less rpm to work with, but I will offset that with longer gearing to keep it in the high numbers longer. My days of riding my best are past me and I really want a long smooth powerband first and foremost. To sum up, my bike is notably stronger (7-8 rwhp) than a typical '09 CRF450. My bike peaks slightly above a '16 KX450F but has less overall power and tq. And a '16 SX450F pretty much whips my bike everywhere by 5hp/ 5tq, but then it does the same on all the other 450Fs.
I have not ridden the bike yet but should get some time on it this weekend and will report back.
The Shop
Way to go Cuz!
It would be fun to have my dyno chart mapped against a newer 350F. Ideally using speed, not RPM as the X axis.
On most carb bikes, Ive learned a large part of poor mileage comes from the vent tubes on the carb, and for that reason the smart carb usually has big improvements in this regard... with issues in others.
And the pilot and needle setting along with float height also really effect mileage. Get it right and big gains can be had.
I posted a mph chart for sunpsd on ktmtalk... if he can find a way to drag it over here he can. getting anywhere close to a current mx 350f is a challenge now days for spread of power. but in the right hands he makes enough power to be dangerous against most 450s too
- I was rained out last weekend so still have not ridden the bike since picking it up from Derek. But I'll be at the track tonight. First time on a dirt bike in darn near a year so I don't expect much out of the rider!
- I don't really watch mpg because I ride tracks, but just based on how much fuel I need to add after a 20 minute track session, the Lectron and Smartcarb both use WAY less fuel than a typical carb ime.
- A dialed in bike isn't going to get less mpg, all else being equal. That power is a sign of efficiency.
- Although I have never cared about mpg in the past, I have been invited to do a motorcycle tour in the CO mountains next summer so all of the sudden, it really matters as I'd prefer to take my own bike! There might be an EXC fuel tank in my near future! The fact that the bike is back on pump gas is huge as well when considering a motorcycle tour.
Pit Row
I also had dropped to 13/ 47 gearing in an attempt to spread the powerband out, a gear set up that previously I could never get to work well for me as it just wouldn't pull well enough on the shifts unless I got it all just right.
Lastly I was burning through the 50/ 50 race fuel mix I had just mixed up for Derek to test with. Remember he ended up tuning on pump gas and the bike made more power everywhere on the pump fuel. But I wasn't going to throw it out! I didn't even change the jetting for the race fuel just cause I don't want to get off track again. But it was a bit rich.
Bike ran killer. Smooth strong tq everywhere with good top end too. The gearing is a really nice fit for this powerband. The bike was fast but easy to ride.
I'm pleased! I'm eager to ride it on pump gas actually! More power.
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