2017 KTM 300XC Rebuild

The Ultimate Trail Bike?

Story by Trevor Hunter, Photos by Trevor Hunter/Ryan Nitzen

Jay’s build is a stunner on the stand with its unique appearance.

Jay Clark recently reached out to us after he finished refurbing a used 2017 KTM 300 XC and we couldn’t pass up the opportunity to ride a bike we didn’t need to put a T-Handle too. 300cc two-strokes are quickly gaining in popularity in the off-road world for their rideability and lightweight feeling making for a great trail bike. However, their downside is they vibrate quite a bit more than a typical 250cc two-stroke which takes away from their capabilities. KTM introduced their counterbalanced two-stroke engines in 2017 which drastically reduced the vibration feel and in our experience, the counterbalancer completes the 300cc motor. We met up with Jay and his creation at Cahuilla Creek MX for a good mix of fast fire-roads and tight, rocky singletrack.

Jay’s 300XC was built for the rocks and tight singletrack and our testers felt right at home on the neon machine.

Upon first sight, we could hardly recognize Jay’s KTM build. The bright neon Polisport plastic looked pretty trick and offered a breath of fresh air in a sea of orange these days. He then explained the mighty list of changes he made to the bike. Remember, Jay works with a long list of companies and he packs as many parts onto a bike as possible. Of course  with a goal of, as he likes to say, “increasing its durability and reliability in the toughest terrain while maintaining the favorable characteristics of a 300cc two-stroke.” Spoken like a waiter spinning top shelf wine. How are you going to make a KTM 300 better? Jay’s unique mods were Dunlop’s AT81 EX Gummy rear tire, Tom Morgan Racing head mod, and a Keihin 38mm Carb with a JD Jet Kit.

The Keihin carb is a unique add-on to replace the tempermental Mikuni.
Dunlop’s AT81 EX Gummy tire hooked up in the rocks and is a huge advantage in the technical terrain.

As soon as we swung a leg over the bike, it felt like a brand new machine. No vibrations and a clean running motor is a two-stroke rider’s dream and that’s exactly what Jay provided us with. Both testers favored the lack of vibration from the crisp motor and the Keihin carburetor cleaned up the jetting to run perfect. 2017 was the first year KTM went to the Mikuni carb and many struggled to find the right jetting specs, but Jay’s Keihin along with the JD Jetting jet kit satisfied our needs on this day. Additionally, the TMR head mods combined with the V-Force 4 Reed Cage gave some extra jazz to the motor making it snappier off the bottom. This feel was similar to a 250cc two-stroke–lively. Where as the typical 300 is a bit more sluggish and slow building. It takes about $1000 in mods to change the power with the head, reed and carb with jetting, for starters. For some comparisons, see the changes we made to a 2018 Husqvarna TC300 over the course getting this type of crisp power.

The bike still retained its abundance of torque only in a more exciting fashion. In the technical sections, the 300 XC worked like a champ where a quick blip of the throttle got the bike over anything we put in front of it.

The TMR head mods didn’t sacrifice the signature torquey power that was needed in the rocks and singletrack.

We’ve had some previous experience with Gummy rear tires in an Endurocross setting, and it can make some of the toughest obstacles a breeze. In the rocks, it hooked up and propelled us up just about anything we set our eyes on, but the it wasn’t quite as favorable in the faster, hard-packed fire roads where it seemed to break traction easier and roll more than we were used to. In the end, if we’re primarily riding in the rocks, there’s no better choice than a gummy tire.

Factory Connection revalved and serviced the suspension and it worked very well for our lighter tester who the bike was set up for (around 160lbs). Compared to my stock 2019 250XC, the 300 was more progressive and a little more compliant for the tight, technical terrain. The 300 XC ate the rocks alive and absorbed all the little hits that stock XC suspension would deflect off of. Additionally, it still held up well on the high-speed roads and absorbed all the small chop with ease. Cahuilla also offered a few whooped out, slower single tracks where dancing on the rear wheel was the preferred technique and the bike tracked straight at all times with no wallowing or kicking.

Factory Connection’s revalve was very comforting yet progressive – very good in off-road settings.

All of the protective guards and pieces from Bullet Proof Designs, TM Designworks, and P3 Carbon did its job with some signs of abuse but ready to tackle more after only a couple of hours in our hands. Also, the 3.5 Gallon IMS gas tank didn’t alter the ergonomics of the bike at all and the Scar Racing Ti Footpegs may ruin our boots in a few rides, but our feet never slipped of the peg no matter how hard we tried. The pegs made controlling the bike with our legs and feet much easier and even took a while to get accustomed to. One thing to note is the heavier feeling of this bike. When riding it back to back with a mainly stock 2019 250 XC, the bike was much harder to steer and make quick direction changes in the tight singletrack. The added weight with the plethora of protective guards along with the bigger capacity gas tank at the helm gave it a heavier feel and was definitely noticed out on the trail. However, the bike felt very planted and connected to the trail at all times.

Overall, Jay’s latest build is leaving us impressed and wishing we could have it for a few more days. It’s performance certainly matches its looks and it may be the ultimate off-road bike. The bike shines in tight, technical rock filled canyons where you can throw the 300 XC in gear and have it pull you up just about anything. It’s added weight with all of the protective guards certainly didn’t go unnoticed, but at times it helped the bike and it gave us a peace of mind knowing it’d be hard to do any serious damage to the bike.

Jay’s Comments:

The goal of this project was to not mess up the best trail bike out there. The 2017-18 KTM 300XC is fast becoming the dream bike for most diehard trail riders with the 2019 model receiving some big chassis/plastic updates.  

The stock KTM 300 XC is a trail bike through-and-through and Jay’s goal was to keep it that way.

I went about keeping the mods simple to the engine and suspension and concentrated on making the bike more durable in tough trail conditions. This bike is truly amazing on the trails and with the Dunlop Gummy rear tire it hooked up amazingly. The power on this bike really rips but is so easy to ride, a guy like Jay can feel like a pro.

The Keihin seems a bit like Fuel Injection for a two-stroke and from what Jay says, it runs just as good at 5000’ with no changes other than a quick adjustment to the air-screw. The JD Jetting Kit gives us a great place to start.    

TMR cut and re-shaped the head for added compression and to help the bike with a bit more power but still be easy to ride. We also added more tooth to the rear to help on the tougher hillclimbs.   

The 300 had plenty of power for both slow and technical and fast and flowy terrains.


Parts List:

Vertex Pistons                  


Pro Replica Piston kit  (Ring, Pin and Clips)

FMF Racing                                                   


Gnarly Pipe/Shorty Silencer  



Head Mod (Can run on 91 pump gas) $129

Cometic Gasket           


Top-End Gaskets



Front – 14T

Rear – 51T Gold Stealth Sprocket (+1 Tooth From Stock)

Gold Enduro O-Ring Chain  



V-Force Reed Cage      

JD Jetting


Jet Kit— Red Needle #2 $84.95




38mm Keihin Carburetor $368

P3 Carbon                                   


Carbon Pipe Guard  

Carbon Skid Plate

All Balls                  


Throttle Cable



3.5 Gallon Oversized Fuel Tank

Coolant Catch Can

DeCal Works                                     


Semi-Custom Graphics Kit with Toxic Yellow                   

Pre Printed Number Plate Backgrounds         

Works Connection                                 


Factory II Stand   

Front & Rear Master Cylinder Brake Caps

Clutch Master Cylinder Cap

Rotating Bar Clamp

Steering Stem Nut

Rear Chain Adjuster Blocks

Dunlop Tire                                                


Front – AT81 – 90/100-21

Rear – AT81 EX (Gummy) – 110/100-18 $110 on RMATVMC.com

Uni Filter                                                    


Air Filter                                      



Titanium Footpegs  

TM Designworks                                


Rear Chain Guide

Hinson Clutch Components             


Full Clutch Set Up/Outer Cover



Radiator Bracing           

Moto Seat                                 


Custom Cool Seat Cover

Trail Tech                                           


Radiator Fan                                                                    

Motion Pro                                                 


Titan Throttle Tube

Grip Glue



604 Fat Bars                                 

Tacky Grips

Cycra Racing                                     


CV4 High Pressure Radiator Cap

Ultra Pro Bend Hand Guards

Bullet Proof designs                               


Swingarm Guard

Rear Disc Guard

Tusk Off road                         


Oversized Rotor/Adaptor Bracket

Factory Connection                        


Suspension Rebuild/Service

Malcolm Smith Motorsports


OEM Parts

Good Deal On Bike

Klotz Synthetic Lubricants               


R-50 Two-Stroke Pre-Mix

Fasst Co


Rear Brake Return Spring

Rear Brake Clevis



Flo Yellow Plastic Kit

Enduro Engineering


Clutch Cylinder Guard