2017 Honda CRF250 Swap-Out Mods: Throttle Body And Fork

We modify the CRF250R for our Long Haul Update

2017 honda crf250r
Steve Boniface riding our uniquely modified 2017 Honda CRF250R, which featured a KTM 250 SX-F 44mm throttle body and a Yamaha KYB SSS spring fork.Sean Klinger

This article was originally published in the December 2017 issue of Dirt Rider.

Primary Use: Motocross practice days

Main Mods: Throttle-body replacement and KYB SSS fork

Moment of Glory: Successfully installing the KTM throttle body and getting it to run well with only the Honda ECU and PGM-FI tool

Forgettable Experience: Overestimating the bike's power on the first lap and trying to jump everything like I was still on the Husky 350 I'd been on that day

Hours: 22.3

Aftermath: Three oil changes, three air filter cleanings, two sets of Dunlop MX3S tires

The CRF250R has gone relatively unchanged since the reintroduction of dual exhaust in 2014. This bike continues to be a good competitor with decent power and a lightweight feel to the chassis. And with that light and compact-feeling chassis this bike seems to be a little more at home on shorter, tighter tracks.

The stock suspension was accommodating to a wide range of our test riders. A nice feature of the Showa TAC fork is how adjustable it is. Adjusting more or less air depending on the rider’s weight is a great benefit similar to how the rear shock spring is also adjustable for various rider weights.

It was not until we began approaching the end of our Long Haul term that we decided to test some mods on the CRF250R. After asking around to see what race teams are changing, as well as looking at some of the factory bikes, we became curious about one of the modifications we noticed. It appeared that some of the bikes had a different throttle body. Conducting further investigations, we discovered they were using the KTM 250SX-F 44mm throttle body.

We managed to get our hands on one of these throttle bodies, along with the necessary connectors, and proceeded to install it on our testbike. After numerous attempts to achieve the correct mapping, we had it running pretty good. (The maps are wildly far from stock, but if you make this mod yourself and want some direction send your questions to drmail@bonniercorp.com.)

In addition to the throttle-body swap, we decided to make a suspension swap too. Because most of our test riders love the Yamaha’s KYB SSS spring fork, we decided to try to bolt them onto the CRF250R. Fortunately, they bolted right on along with the Yamaha front wheel and front brake. We then took the CRF out to a few tracks to see what we’d created.

After a little more fine-tuning to the EFI mapping and some sag adjustments, the bike was ripping. The KYB fork worked excellently on the tighter tracks such as Milestone and Perris. Their plush feel made the CRF corner even better than with the Showa TAC forks. The engine seemed to have just a little more throttle response, helping with a little more pop out of the corners.

We also tested these mods at Glen Helen, a more wide-open track with long hills and some loamy corners. We did notice a few differences in the chassis that needed a little work. With the KYB fork being so plush, we had to run much more than the normal sag. With the sag set close to the recommended 105mm we found the bike to be slightly unstable at high speeds and under braking down the hills. We opted for 112 to 115mm to help correct this problem but found that the shock became a little harsh, possibly from riding too far into the stroke.

Our conclusion of the mods was that the throttle body helped the engine’s overall rideability, but it didn’t really increase the horsepower. The KYB SSS fork was an improvement over the Showa TAC fork, but depending on your weight you may need to change springs. A lighter rider may benefit from a softer shock spring, while a heavier rider may prefer stiffer fork springs to help balance out the chassis.

Overall, the testing was fun and the Honda improved with the mods…but not by a whole lot. We think that when considering cost and effort of this approach, most riders would be better off seeking the more traditional routes to improving their CRF250R. So view this as a case of us doing the experimenting so you wouldn’t have to and answering a couple questions we’ll bet some of you have wondered about.