On this week’s Two-Stroke Tuesday we take another look with some unseen photos of a very unique Yamaha YZ345 built by fabricator Howard Jenkins of MotoFab Industries located in central California. Could you imagine a YZ250 two-stroke engine dropping right into a newer Yamaha four-stroke chassis without any major frame modifications? Well, it might just be possible! The topic in our 2-Stroke History section this week is Suzuki’s RM250 and could it be the best used bike ever. Don’t miss our Behind The Build of Mike Browns FXR/Rockstar Yamaha YZ250 at the bottom of this post!
So what if we told you a Yamaha YZ250 two-stroke engine would fit into newer four-stroke chassis without cutting huge sections of the frame away? True story 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.
This is our first build with the 345 kit the MotoFab crew has done 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 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.
With more than a year of development the MotoFab intake for the YZ345 has been finalized. This one piece carbon fiber system utilizes the stock air box placement providing a larger volume of air in the system before being restricted by the air filter and is giving better performance on the bottom end. 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’s connected to the intake boot 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.
This YZ345 has a unique wide ratio transmission setup featuring YZ 1st and 2nd gears and WR 3rd, 4th, and 5th. The WR 1st gear the MotoFab crew felt was too low and love the combination of YZ 2nd and WR3rd because the YZ 2nd and WR 3rd are more closely geared than the stock setup from either the YZ or the WR and give a great combination for woods or trail riding.
With Yamaha focusing so much on centralizing mass for the four-stroke version the MotoFab crew positioned the YZ250 two-stroke 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. They hope it gives the bike a more “planted and stable” feel.
The story of the Suzuki RM250 isn’t just about a single motorcycle. It’s about a dynasty of bikes, championships and riders that goes back to a glorious era in the history of motocross. Click the image below for the full story!
2-STROKE BEHIND THE BUILD
Mike Brown has raced at the highest level of motocross, Supercross and off-road for factory-level teams during a career that has spanned over three decades. The 47-year-old racer is no longer competing to put food on the table, but is now doing selected events for Yamaha, FXR and Rockstar Energy just for fun. Click the image below for the full story!