The Link Between Throttle Response, Horsepower Loss, and Reed Petal Performance.
An Observed Trial machine’s overall engine performance (it’s ability to achieve consistent acceleration response and peak horsepower), is directly linked to the performance of its reed petals. Twostroke Observed Trial engines receive air and fuel mixtures through a mechanical intake system that is commonly referred to as a Reed Valve.
Reed Valves are almost always located between the carburetor/throttle body and your machine’s engine, and are designed to work in conjunction with a system of delicate, pre-mounted reed petals. Together, the Reed Valve and the Reed Petals create the heart of an Observed Trial machine’s intake assembly. The small, flexible Reed Petals are primarily responsible for controlling the inlet of air and fuel by the simple process of opening and closing against the surface of the Reed Valve. Because Reed Petals are responsible for the ongoing regulation of air and fuel into the engine, they are the single-most crucial component within your machine’s air-intake system. They are the flexible component of the Reed Valve that “reacts” to the engine’s cycling piston – this engineering fact makes them… “The Gatekeepers of Power”.
REED PETAL FUNCTION
To regulate incoming air and fuel in the proper ratios required for performance, Reed Petals are designed to “reactively pulse” as the engine’s pistons cycle through their intake and exhaust strokes. This reed petal pulsation, or “FLEX CYCLE” occurs at a one-to-one ratio in unison with the upward and downward movements of the engine’s piston. Within each reed petal flex-cycle, the petals are designed to flex open in unison with the piston to allow air and fuel into the engine. The petals then briefly close, precisely “kissing” against the surface of the Reed Valve to stop the internalized air and fuel from backwashing, or “reverting” out of the engine. This process is commonly referred to as “Reed Petal Trapping” and is one of the performance tuning areas that influences a Reed Valve’s ability to supply the engine with the proper air and fuel mixtures needed to optimize power and acceleration response.
Throughout their life span, Reed Petal flexes millions of times. Because of this continual strain, all Reed Petals individual composite fibers start to lose their memory, deform, and/or ultimately chip at their edges making them slow to react in unison with the engine. When reed petal degeneration occurs, most, if not all reed petal designs, regardless of materials used, are unable to properly trap the air and fuel charges in unison with the engine’s pistons. In this regard, failing to manage air and fuel “reversion” is a known cause of decreased engine performance and can easily be remedied by changing to a new set of Reed Petals.
REED PETAL LIFE EXPECTANCY
An Observed Trial machine’s Reed Petals should be considered a maintenance item that needs periodic attention in order to keep your machine’s engine performing to optimal levels. If they are not periodically inspected and replaced, they will begin to contribute to a number of poor performance symptoms including hard-starting, easier engine stalling, loss of response and power, and will also produce inconsistent power delivery. Inspecting your machine’s Reed Petals periodically is a quick, cost effective, and easy do-it-yourself maintenance project that ensures your engine is receiving the proper air and fuel mixtures required to achieve consistent power delivery and obtain peak horsepower output time-and-time again. Reed petal life expectancy varies dramatically with your machine’s engine and intake design and also varies greatly depending on how hard or how often you ride. Someone who is always on the throttle, allowing the engine to constantly run at high RPMs can expect less life from their reeds petals. If you ride for long hours, then it is a good idea to check your Reed Petals 2-3 times a season to ensure maximum horsepower output is maintained.
TECHNICAL ARTICLE HOW TO CHECK YOU REED PETALS CHECKING YOUR TRIAL MACHINE’S REED PETALS
When checking your reed petals, look for edge chipping, surface tears, cracking, or a peeling of the surface material. Also, check to see if the Reed Petals are maintaining their static gap against the Reed Valve surface.
STEP-BY-STEP GUIDE TO INSPECTING REED PETALS.
Inspecting the Reed Petals on an Observed Trial machine first involves getting access to the Reed Valve unit. This will require you to remove the carburetor and the Reed Valve Assembly from the engine. The process is fairly straightforward and can be performed with basic tools. If done correctly, you should be able to finish the job in about an hour. Unbolt the carburetor or throttle body, remove the Reed Valve from the engine and inspect the entire assembly. If the assembly’s petals are pulled away from the cage, cracked or have rough edges, the petals should be replaced.
REMOVE SUBFRAME, AIRBOX AND CARBURETOR
1. Remove the integrated Airbox/Subframe Assembly by locating and removing all Subframe bolts as well as the rear brake light wiring harness plug. Locate and loosen the Airbox to Carburetor intake clamp bolt(s). At this moment the Airbox/ Subframe should be ready to remove from the machine.
2. Locate and loosen the Carburetor to Reed Valve intake clamp bolt(s). While noting the cable routing of the throttle cable, gently pull the carburetor towards the back of the bike. The Carb will release from the Reed Valve Assembly’s intake boot. You do not have to remove ANY throttle cable connections to the carburetor; just set it aside.
REMOVING THE REED VALVE ASSEMBLY. COMPONENT INSPECTION
3. Locate and remove the 4 Reed Valve Assembly bolts. Remove Reed Valve
Assembly from engine. 4. Locate and remove the 4 small screws that hold the two Reed Petals and the Reed Stops on the Reed Valve Assembly. After removing the petals and the stop, inspect the Reed Valve for foreign material between the Reed Petals and the Reed Valve’s petal surface junction. Also inspect the Reed Petals for ANY deformation or surface damage, looking precisely for chipping at the tips of each petal.
INSTALLING BOYESEN REEDS
5. Install new Boyesen Carbon Tech or Boyesen Power Reeds and all required components to the Reed Valve Assembly using thread locker to ensure that the screws stay in place during operation. NOTE! If you are installing Carbon Tech Reeds you will use the stock Reed Stop. If installing Power Reeds, you will replace the stop Reed Stop with the included Boyesen REV Plate. Use of the stock Reed Stops with Boyesen Power Reeds negates the performance of the Power Reed design. 6. Take care to install the new Carbon Tech Reed Petals and Reed Stop symmetrically on the Reed Valve. All Reed Petals and Reed Stops should symmetrically align on the valve, totally covering the intake ports, and maintain alignment with the Reed Stop. WARNING! MAKE SURE that all the screws have been covered with thread locker and all have been tightened well. This will ensure that the screws will not back out and be sucked into your machine’s engine causing it to be damaged.
REINSTALLATION OF THE REED VALVE ASSEMBLY
7. Reinstall the Reed Valve Assembly. Tighten Reed Valve Assembly bolts in a criss-cross pattern to your particular machine’s manufacturers specifications. Optimally, new Reed Valve gaskets should be used if the existing gaskets show tearing or delamination. Inspect all gaskets carefully to confirm proper condition. 8. Reinstall Carburetor/Throttle Body. Make sure that the Carburetor/Throttle Body is vertically orientated and is set at the 12 o’clock position relative to the engine. WARNING! MAKE SURE that the carburetor is set well inside the intake boot. MAKE SURE that the clamp fits evenly and securely around the entire boot surface. Failure to install the Carburetor/Throttle Body proper into the intake boot can result in an air leak, ultimately creating a lean condition in your machine’s engine. 9. Reinstall the Airbox/Subframe on the machine taking care to ensure a proper fit of the airbox boot on the Carburetor/Throttle body. If you are running the rear brake light, remember to plug in the wiring harness. WARNING 1! MAKE SURE that the carburetor is set well inside the Airbox Intake Boot. MAKE SURE that the clamp fits evenly and securely around the entire boot surface. Failure to install the Carburetor/ Throttle Body proper into the intake boot can result in an air leak, ultimately creating a lean condition in your machine’s engine. WARNING 2! MAKE SURE that the Throttle Cable routing is the same as when you removed the Airbox/Subframe. Check to make sure that the cable did not partially release from the carburetor’s cable housing located at the top of the Carburetor. Trial Magazine and Boyesen would like to thank Gas Gas Motos UK for helping with the generation of this article
2013 British Champion Michael Brown (300cc JST Gas Gas) “To compete at the cutting edge of the sport it’s essential to me that any aftermarket parts fitted are tested before using them. None of the parts make a huge increase in the machine’s...