How do you know if you need a new set of reed valves?

 

I would just take them out, and look them over.....to make sure you don't have any cracks. It's easy to get them in and out.

 

The reeds in a 2 stroke really just act as a one-way valve. The fuel/oil/air mix comes in from the carb, past the valve and into the crankcase where the oil part of it lubes the bottom end of the engine (lower rod and crank bearings). It then travels up to the combustion chamber where it ignites and makes power. The oil part of it has done its job and is no longer needed, but you can't separate it out so it just gets burned. Thus the smoke of a 2 stroke engine. But as that fuel/oil/air charge is on the trip to the combustion chamber, another charge is coming into the crankcase. That is what makes it a 2 stroke engine, versus a 4 stroke where each has its own cycle. Anyway, since one flow is coming and one is going all at the same time, the reed valve keeps the first one from blowing back into the carb.

More than you wanted to know? Well, you can see that a weak reed valve would allow blowback into the carb, and therefore less fuel/oil/air mix into the engine. Less fuel = less power. So if your quad seems down on power, that could be one indication of a weak reed valve (it could also be about a hundred other things!). The thing is, as RAJ said, its easy to get it out and even to change them. Just be really careful to not over-tighten the little screws that hold them in the cage. Use locktite to hold the screws, not a lot of torque. Unless your old reeds are cracked or broken, new ones won't give you eye opening improvements. Probably just a little quicker response and smoother running.