This weeks Two-Stroke Tuesday has a exclusive first time look at MotoFab Industries radical YZ345. You don’t want to miss what owner/fabricator Howard Jenkins has to say! We have premix necessities from Maxima oils, Uni filters and Athena. Enjoy all the amazing sights and sound of 2-Stroke Theater featuring a couple YZ250 projects, Mike Allessi’s RM250 and the head-to-head battle of two iconic Kawasaki’s. Don’t miss an exclusive link to a very trick 300cc KX located at the end of this post.

 Howard Jenkins CEO of MotoFab Industries in central California had a customer that really wanted to make this bike a reality and he was excited about the challenge of creating something truly different. Here is some insight from Jenkins on the build specifics.

Who doesn’t love carbon fiber?  MotoFab has been working on this intake system design and execution for nearly a year now.  After many molds have been thrown in the trash (usaually pulled out the next day) we have finally completed the mold to make this intake system in a single part made out of carbon fiber.  The system has a rubber grommet that presses into the opening of the part at the carburetor that allows for the OEM air boot clamp to make the seal.  At the other end it is connected to the intake boot (Also a Motofab carbon part) with a small section on silicone turbo hose that gives the system the ability to flex.  Attachment is made to the sub-frame with molded carbon tab at both sides of the subframe.   From the testing we have done, this intake provides a larger volume of air in the system before being restricted by the air filter and is giving better performance on the bottom end.

Big Bore & Wide Ratio: We have been building our YZ 250 engine builds with the ESR325 cylinder kit for some time now.  This is our first build with the 345 kit and are excited to feel it put power to the ground.  Eddie Saunders (ESR) designs and manufactures the entire cylinder kit in house except for the casting which he has casted here in California.  The most unique aspect to the cylinder is the power valve design.  The main exhaust port actuation is driven by exhaust pressure and can be adjusted to fasten or slow its operation based on the spring tension.  The two exhaust side ports are open all the time with no actuation at all.

For the wide ratio transmission setup, I have installed the YZ 1st and 2nd gears and WR 3rd, 4th, and 5th.  For the reasons that the WR 1st gear is too low and I love the combination of YZ 2nd and WR3rd, this is my favorite setup.  YZ 2nd and WR 3rd are more closely geared than the stock setup from either the YZ or the WR and give a fantastic combination for woods or trail riding.

The design for the intake system was derived from studying Yamaha’s design in the first years with the reverse cylinder.  On the first 450, they had the shock reservoir horizontal and the exhaust wrapped around behind the shock.  We decided to take some inspiration from this design, but wrap the intake around behind the shock instead of the exhaust.  The first order of business was to get the shock reservoir out of the way by modifying the shock changing it to a remote reservoir system. Positioning was critical to maintain accessibility to the clickers.

Motor position: There have been a lot of negative reviews regarding the handling of this four stroke bike.  With all of the work that Yamaha has put into “Centralizing the Mass” on this four stroke model, there seems to be negative effects to the front end feel on the bike. This was another aspect of this build that we were excited to see if the two-stroke engine could correct.  We positioned the YZ250 engine as low as we could in the chassis wanting to keep the weight low. With the much shorter 2-stroke engine and forward facing cylinder, the motor weight in the bike is lower and further forward.  We hope that this gives the bike a more “planted and stable” feel.

For the finish on the cylinder and cases,  I send out to a local company locally that Vapor Hones our parts.  On the cylinder, I get the raw casting from Eddie before they are machined and have the cylinder vapor honed using a more aggressive media to remove the rough sand casting and then finish it with a fine micro glass bead media.  I use the same micro glass media on the engine cases. The media for this finish is so fine that it actually closes the pores of the material causing the finish to hold up a long time.



For over forty years, Uni Filter Dirt Bike Foam Air Filters have been unsurpassed in both engine protection and overall performance. And their unique two stage design produces MORE HORSEPOWER and MORE TORQUE than any other air filter.

Retail Price : $ 34.95

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CASTOR 927 is a unique blend of highly refined castor oil, a specially prepared synthetic and an additive system that reduces carbon and gum formation and provides excellent rust & corrosion protection. Contains an exclusive additive that keeps power valves cleaner and working properly. Keeps lubricating and fights carbonizing or vaporizing Provides extra protection on cylinder walls, bearing journals and other critical areas at high temperatures.

Retail Price : See Your Local Dealer

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  • Kits include aluminum cylinder with nickel-carbide coating designed with larger water jackets
  • Forged piston black graphite or clear tin coating; includes rings, clips and pin
  • Athena top-end gasket set includes required seals and hardware
  • Easy-to-follow step-by-step installation instructions
  • Most are bolt-on; no machining required except where noted


  • Athena top-end gasket set including required seals and hardware
  • Easy-to-follow, step-by-step installation instructions
  • Two-stroke kits feature specially designed, high-performance, hard-anodized power valves (cannot use OEM)
  • Include aluminum cylinder with nickel-carbide coating, ported to Factory Works specs
  • Specially designed, high-performance, Cast-Lite flat-top piston kit
  • Two-stroke kits include an aluminum cylinder head with a removable bronze dome allowing for a higher compression ratio and anti-detonation features (except where noted)


  • Athena top-end gasket set including required seals and hardware
  • Easy-to-follow, step-by-step installation instructions
  • Specially designed, high-performance, forged OEM-style domed piston kit
  • Specially designed, high-performance, hard-anodized power valves (cannot use OEM)
  • Include aluminum cylinder with nickel-carbide coating

Price: $1295.95

Contact: Your local dealer or


Want to see a sneak peek of MotoFab Industries KX300AF? Click the image below for more! 



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