How to Inspect and Service Reed Valves
November 14, 2012
Filed under How To
Reed valves might be one of the most neglected parts on a two-stroke snowmobile. That’s too bad because many snowmobilers might be giving up performance or dealing with an engine that’s hard to start because of worn reed petals.
Research online showed that new reed petals are available from Arctic Cat, and Ski-Doo factories for about $25. Petals from Yamaha were considerably less expensive. Availability of Polaris reed petals is limited to some fan-cooled models that have cylinder reed induction; complete reed cage assemblies are available for Polaris liquid-cooled engines for about $100. Boyesen and Moto Tassinari have a variety of reed valve systems available.
Laziness or hatred of all things intake probably isn’t the reason reeds are ignored, but instead it’s more likely because they’re hidden between the airbox and the engine, which itself is harnessed under wires, hoses, cables and a steering post, especially on snowmobiles built in the past five years or so.
No matter how you eventually get to the reeds on your sled, inspecting them is the same for any engine. Here’s how we removed and reinstalled the reeds on a 2002 Polaris 600 XC SP in the EDGE chassis, along with a rundown of the purpose of reed petals and how to inspect them.
Before final assembly, use a shop rag and carburetor or contact cleaner to wipe the oily grime inside airbox. Reinstall the intake tube, carburetor adaptor plate and other related airbox parts as necessary. Similar to Step 8, make sure rubber flanges of the intake plate completely surround the bell of the carburetor so they don’t cause a lean condition. Make sure throttle cables and vent lines are routed correctly — no pinches, no kinks — and then test run the engine.
First hook up the fuel lines, vent lines and oil lines as necessary. It won’t be necessary to bleed the oil line because the air pocket is down-line from the oil pump. With the lines hooked up, push the carburetors into the adaptor boots, making sure that they are bottomed out and that the boots completely surround the carburetor. Our Polaris was easy to see that the parts were installed correctly, but other machines aren’t. Use a flashlight to carefully inspect and confirm the boot isn’t folded over so it will create a lean condition.
Reinstall Reed Cages
Before re-installing the reed cages, clean the mounting surface on the crankcase or cylinder to ensure a good seal. Some aftermarket reed systems use gaskets. Start the mounting bolts by hand and then evenly torque the hardware to specification for your engine.
If the petals are damaged or worn, they should be replaced. We replaced our stock setup with a new set of Moto Tassinari VForce 3 reed cages. Aftermarket companies claim their reed systems boost throttle response or peak horsepower; whether you replace the petals with stock parts or install a new system is up to you.
Inspect the reeds for damage. Reed petals from our Polaris were in decent shape, especially considering that there were almost 6,000 miles on the sled. Most of the petals rested tightly against the cage, but they were starting to pull away at the center, bottom row of each assembly.
Remove Reed Cages
With the carbs off, the carburetor adaptor boots that contain the reed cages can be removed from the crankcase by twisting out the bolts on each combustion chamber. With the fasteners removed, pull the reed cages out of the engine for inspection.
With the lines disconnected, loosen the hose clamps that hold the carburetors in the boots on the engine and set them off to the side. Position the carburetors upright so fuel doesn’t drip out.
Unhook Fuel/Oil Lines
Unplug the throttle position sensor (TPS) from the carb rack; our sled’s TPS was on the mag cylinder’s carburetor. Unhook each oil line from the carburetors and then unhook the fuel line from the ‘T’ fitting on the bottom between each carb. Plug each line with a golf tee, center punch or similar device to prevent oil and fuel from dripping. Unplug the two vent lines that attach to the airbox from the carbs.
To access the reeds on our case-reed inducted Polaris, we removed the top of the airbox, pulled out the intake tube and then removed the plastic plate on the front of the airbox. The rest of the airbox can stay in the sled.
Want to learn more about snowmobile engine reeds? Learn more in Engine Reeds 101!