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Author Topic:   Reed Valves: Signs of Problems
Canibul posted 05-22-2006 05:31 PM ET (US)   Profile for Canibul   Send Email to Canibul  
What are the symptoms of a gummed up or carbon fouled reed valve? I have just found out that no de-carbonizing additive (as in not a single can) has been run through mu engine in about nine years. I don't think it is gummed, but how does a reed valve not completely closing would affect performance and mileage?
bsmotril posted 05-22-2006 07:09 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Reed valves don't get carbon fouled since they sit between the carb and the crankcase, well away from any combustion. I've never seen one gum up either, though that is not to say it is not possible. If they do have problems, they usually break. The symptom is a misfire under load and very rough running motor, though it might run fine on flushing muffs with no load. I'd be more worried about the rings if it has not been de-carbed in a long time. That clogs the back of the rings with carbon causing them to stick in the grooves. Clean rings use expanding combustion gases to get behind the ring and push it out to seal the piston to the cylinder. Dirty rings don't do this and the motor will be down on power. Get a compression gauge and check your cylinder compression. That will tell you if you have poor compression and leaky rings. BillS
sosmerc posted 05-23-2006 12:36 AM ET (US)     Profile for sosmerc  Send Email to sosmerc     
The condition of your reeds in a 2 stroke outboard is indeed very critical to proper running quality and performance. If a reed is broken, fractured, or is like having a hole in your engine...and fuel cannot be properly delivered to the affected cylinder.
It is most noticeable at idle and low speed.
Also, if the reeds have been installed improperly (over tightened or "pre-loaded") the engine will not run cleanly at idle, and may accelerate poorly.
On engines that have check-valve bleed fittings in the intake manifold it is possible to put a pressure guage on the bleed fitting and monitor the crankcase pressure...extremely low or erratic pressure would indicate a reed problem...or a bad manifold gasket or loose reed block. If you get fuel droplets spitting out of the front of the carb at idle...that's a good sign of a broken reed.
Proper ring seating and sealing is also critical to 2 stroke engine performance. Regular use of additives such as Quickleen, Techron, Ring-Free, etc help to keep the ring lands clean and carbon free. Excessive carbon buildup behind the rings will cause "ring Jacking"...where the rings cannot spring properly conforming to the shape of the cylinder...thus they score the walls and create paths for the compressed mixture to "blow by" the rings...this leads to low compression and high leakdown numbers. A proper leakdown test will reveal this problem more easily than a compression check. I have seen engines with fairly normal compression numbers, but their leakdown numbers were very high, and the teardown revealed scored walls and scored piston skirts and nearly stuck rings due to carbon buildup in the ring lands.

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