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2017 Honda CRF250R — HonKTMaha

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We all wonder these things, right? What if you took this off that bike, and that off this bike, and mashed them all together to make one incredible machine? Well, like a proverbial Dr. Frankenstein, that’s what we did.

We began with the stock 2017 Honda CRF250R because, to be honest, it wasn’t getting much ride time. We asked ourselves, “Why don’t we want to ride that bike given the choice of all the other bikes?” The main answer is the ’17 CRF250R is exactly the same bike as the ’16, and that means it still had the Showa SFF-Air TAC fork, which pretty much no one liked. Plus, it is a tad on the mellow side, motor-wise.

In a moment of brilliance—or complete stupidity—we thought, “Hey! What if we poached the top bikes in the 250F Motocross Shootout to make the Honda better?” The winning machine for the 2017 250F MX Shootout was the Yamaha YZ250F, and one of the main reasons it took the top spot on the podium was because of its KYB SSS fork. Luckily for us, and for you, the YZ-F fork has the same outer tube diameter as the Honda’s even though the lower tubes have different diameters (48mm on the YZ-F and 49mm on the CRF-R). But swapping the forks isn’t as easy as it sounds. The Honda has a 20mm axle and the Yamaha has 22mm axle, therefore the stock Honda front wheel won’t fit in the Yamaha fork lugs. And even if it did, the brakes don’t match up since the stock Honda front disc is 260mm and the YZ’s is 270mm.

The simplest way around this, and the way we did it, is to steal not only the fork from the Yamaha, but the front wheel and front brake, including the cable and lever, as well. From a practicality standpoint, this might be too expensive for a lot of budgets because that’s a lot of stock Yamaha parts for a Honda owner to buy. Another option is find a 2012–’13 YZ250F fork because it is essentially the same as the 2017 fork, just with 20mm axle lugs that would fit the Honda’s front wheel. We aren’t certain what size brake rotor came on that bike, so you would have to make sure those line up. Lastly, if somehow you found a ’14-or-newer fork, you could then call suspension shops to see if they have any ’13 or ’12 fork lugs. Fork lugs are screwed on to the lower fork tubes but require special seals—not a do-it-yourself job.

The second-place finisher on in the ’17 250F MX Shootout was the KTM 250 SX-F and we’ve heard of some race teams putting the KTM Keihin throttle body on the CRF250R to help in the motor department. The main difference between the throttle body that comes on the Honda and the one that comes on the KTM is the position and angle of the fuel injector. On the CRF-R, it is on top of the throttle body pointing at a 45-ish-degree angle toward the engine. On the SX-F the injector is on the very bottom of the throttle body pointing straight up. The other difference is that the inlet and outlet diameters on the KTM throttle body are slightly smaller. Normally we think bigger is better, but when it comes to pressure and speed, given the same volume of air, the smaller the diameter, the faster and more pressure the air-fuel mixture will have.

But this is where things got really messy. Like, “if you’re not a professional mechanic, you probably don’t want to try this yourself” messy. Unlike the fork swap, the throttle body swap requires a lot of cutting and splicing of the wiring harness because some of the sensors and plugs used by KTM and Honda are very different. Also, the airboot/throttle body connection is the same, but the throttle body/cylinder connection isn’t. Since this was a temporary mod for us (Honda doesn’t want KTM parts on its bike when we give it back) we used duct tape to make the throttle body diameter match the cylinder inlet.

For a full how-to (if you are that gnarly) we’ll have a Dr. Dirt on this bike in the print magazine that will explain the rerouting of wires, which connectors you have to replace, and all that jazz.

Once we were done playing Dr. Frankenstein, we kicked the bike to life and it worked! Well, sort of. It would barely idle and had rich burble that made it unrideable.

Luckily our tester/mechanic Allan Brown was on the case and started working his magic with Honda’s PGM-FI mapping tool. It’s a CD and you need a laptop and a special Honda connector to plug into the bike. He started by leaning out the fuel mixture, which got the bike to run better and let us know we were headed in the right direction. After eight maps going 2 percent leaner each time, we settled on two that we liked. The stock map selector button let us switch between stock Map 1 (which is locked and not changeable even with the computer), Map 2, and Map 3. Those would work out to be about 14 and 16 percent leaner, respectively. Our tester preferred the 14 percent (slightly richer map) while the faster and pro-level rider liked the 16 percent map.

We tested at both a tighter, smooth, jumpy track (Milestone MX) and an open, fast, rough track (Glen Helen Raceway). First, we’ll talk about the throttle body mod and what we felt. Cutting right to the chase, it didn’t blow us away. The fact that we had to keep going richer told us the KTM-only throttle body was giving the bike a lot more fuel than it was used to, but how crappily it ran (at first) also told us that just adding more fuel to a bike that wasn’t designed for it doesn’t make the bike automatically better. By leaning out as far as we did, we might have been in the same range as the stock throttle body. Or, since the throttle body is completely different, the sensors could have had different starting points which would give us a very different reading. There are a ton of variables and factors and, in retrospect, the fact that we got the bike to run as well as it did is pretty cool.

Did it have better power than stock? Hard to say, really. With the KTM throttle body on and with the lean map that we were the happiest with, we can say it wasn’t worse than stock but it wasn’t noticeably better either. The power character was about the same, it had great throttle response (as does the stock bike) and had wide, sort of flat mid-range power and not a ton of torque down low or power up top.

But then why do some race teams do it? They aren’t just slapping on the part and calling it a day. They are, or at least have the ability to, modify heads, change out pipes, and use different software and hardware (ECUs) to tune their machines. We could only operate within the limited boundaries of the stock software and it would defeat the purpose of finding out just what this swap did if we also did a bunch of motor work and slap on a pipe.

Hang on a sec… Before you stop reading in frustration, we haven’t got to the fork yet, and we’ll be equally forthright—yes, there is a vast improvement. The KYB SSS fork immediately gave the Honda way more comfort up front and, since the Honda was already a great-cornering bike, the SSS complemented the bike’s turning characteristics quite well. The lug offset is nearly identical on both bikes, so the front axle placement should be the same. If they were drastically different, then the bike’s handling could have gotten way out of whack. Since the SSS fork is so smooth, it felt almost too soft with the stock settings and that the shock was overpowering the fork. This does make sense, since the fork and shock on a bike are developed in tandem. The stock Honda Showa fork had an overall stiff character and needs a shock to match.

Yet all isn’t great in HonKTMaha land. With the sag set at 105mm, each of our three riders felt that the bike, especially the shock, was way too busy. The back of the bike was bouncing around and not tracking straight in the rough stuff, and really wanted to step out at the end of corners with some chop in them. Later in the day, our bigger tester hopped on the bike without setting the sag for him and found the bike handled much better than with the sag at 105, (it was most likely at 110–115). Another tester tried running more sag and confirmed that it helped calm the rear down.

To really test the Franken-Bike we had former pro Steve Boniface come ride with us at Glen Helen. Here is his take on the bike.

“I’ve ridden the stock Yamaha 2017. I haven’t ridden a stock 250 Honda for a long time. So it’s hard for me to compare, like engine-wise, what this one is doing compared to the stock engine. As is, I felt like I want more power from mid to top. The bottom was pretty good. It wasn’t really clear when I was in the meat of the power. Coming into a corner it seemed a little rich or something. I don’t know how the stock bike is, but I just didn’t feel like it was really fast for a 250, like, I wasn’t flying out there compared to other 250s. Considering that I can see some other 250s making all the jumps, I feel like I was lacking and not making the jumps.

“Handling was good. The fork is super nice. That bike turns really good. I don’t know if it’s the bike or if the fork really helped it, but cornering was amazing on the bike. Really comfortable. Really good feeling on the front end of the bike. Very safe. I felt like the front tire was sticking to the ground. I really liked it. I was pretty comfortable riding Glen Helen on stock suspension. No harshness, good plushness, but not too soft for me. The front was way better than the rear. The balance was off. I would really try to make the rear better to match the front. The rear was high for me and really busy. Especially coming down the hill, it was hard to get the bike really sticking to the ground. The rear felt really light and I had a hard time getting it to suck in. It was high and light and busy. But the front is really good, I really like it.”

Nope. We didn’t make an amazing hybrid machine taking only the good things from each bike and none of the bad. The throttle body swap is not worth the amount of work and parts and headache required to even get the bike running. But we do see the potential there for a gnarly engine if someone used this as a starting point then began messing with engine work, more complicated mapping, and then pipes.

As for the fork swap, we would recommend it if you could find the right forks at the right price. Just know that you’ll have to do a lot of work at the track getting the rear to match the front. You’d also want to play with where the fork sits in the clamps because that would affect the balance as well. We also know that Race Tech has a spring conversion kit for the Showa SFF-Air TAC fork that a lot of people have been happy with. That way you aren’t messing with the front-to-rear balance of the bike since that fork and shock are designed to work together.

The biggest lesson we were reminded of and hopefully a lot of you out there learn from this is that bikes are way more complicated than they look. Meaning, they aren’t simply a frame, engine, fork, shock, etc., just thrown together with everything being interchangeable. Most, if not all, of the parts on a bike are designed in unison and aren’t going to necessarily work on other bikes. Race teams do weird, crazy swaps because they have the time, resources, and a very compelling reason to try out different things—they get paid to win. That being said, if you also have the time, resources, and reason, have at it!

What we took from the Yamaha YZ250F:

  • Fork
  • Complete front wheel including brake rotor
  • Front brake assembly (caliper, cable, master cylinder, and lever)

What we took from the KTM 250 SX-F:

  • Throttle body
  • Wiring harness (to be cut up for connectors)