Duncan Racing International, Inc. has a combined 80+ years of experience in the Motorcycle/ATV industry performing the highest quality 4-stroke cylinder head services in the nation.

DRI offers all head services In-House: 
Porting, Valve Guide Removal and Replacement, Valve Seat Machining on Serdi Machine, Flow Bench Testing, Seat Repair/Replacement, Custom Head Welding and Repair, Valve Spring Testing, Stock Head Rebuilding and Servicing. 

DRI has made it's name in the ultra competitive field of ATV Racing, winning numerous World and National Championships over the last 25+ years. Although DRI is famous worldwide for their ATV performance. DRI also has extensive background covering many other type of Motorcycle performance,including but not limited to modern day 4-stroke MX and Off-Road motorcycles, Vintage Japanese Street Machines and Vintage British Twin Cylinder Street Machines.

Following are some information files on the more popular models DRI offers cylinder head services for. If you do not see your machine listed call DRI 619.258.6306 and ask for Loren Duncan.



YAM 450F (coming soon)

Yam YZ 250F
Yam YF 400/426
Yam WR/YZ 450 '03-'09 
Suz RM-Z250
Hon CRF 450 '02-'08
Hon XR/XL 600
Hon XR 650R
Hon 750 SOHC
Triumph 650/750 Unit Construction Models