Reeds

spincycle

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Im kinda of a newbie with a reed motor...What may be some of the signs that the reeds in the reed cage need to be replaced?....stock 125 sudam....thx!
 
I raced McCullough's for 10 years, fairly successfully, and I have no stories about what I felt when the reads went bad. Of course I checked them all the time, so they had little chance to go really bad. I raced 91's, 101's and 91 reed opens.
 
Ditto on the hard to start but I have found that amazingly they will run otherwise OK with big chunks gone and cracks. Nothing beats inspecting them regularly. In fact the first thing I look at when the tune changes more than just a bit for the altitude density is the reeds.
 
The one time I had a broken reed, it would run ok midrange and top end, but bottom end had a stutter that couldn't be tuned out with the carb, and poor accelleration through the first third of the RPM band....also hard to start. Thought it was ignition issue for a while, 'til I checked the reeds. Carbon reeds I'd check for pinholes and once I saw more than 4-5 per side, I replaced...
 
On my dyno, a Go Power water break, in the mid-80s, I noticed an anomaly in the torque curve of a Reed valve Komet, in the lower RPM ranges, that I could attribute to only one thing. I believe that was a indication of a transition point where the reeds stop closing completely and where they stayed open all the time. Just conjecture, no real proof. I have heard stories of McCullough's, on a road course, completely losing the reeds and never showing any symptoms until the end of the race.
 
Reversion is simply the flow of exhaust gasses back into the combustion chamber when the downward movement
at the piston creates a vacuum in the cylinder. This event occurs when a camshaft is on the overlap, ;ie the exhaust
valve is still open as the intake stroke begins.

So on a 2 stroke with no valves (weed eaters have valves) but with reeds that are bad/damaged the result is fuel spitting out the carb?
 
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Reversion is simply the flow of exhaust gasses back into the combustion chamber when the downward movement
at the piston creates a vacuum in the cylinder. This event occurs when a camshaft is on the overlap, ;ie the exhaust
valve is still open as the intake stroke begins.

So on a 2 stroke with no valves (weed eaters have valves) but with reeds that are bad/damaged the result is fuel spitting out the carb?
Another name for it fuel standoff . A serious case looks like a thick fog blowing out of the carb inlet.
 
The one time I had a broken reed, it would run ok midrange and top end, but bottom end had a stutter that couldn't be tuned out with the carb, and poor accelleration through the first third of the RPM band....also hard to start. Thought it was ignition issue for a while, 'til I checked the reeds. Carbon reeds I'd check for pinholes and once I saw more than 4-5 per side, I replaced...
what could cause "pin holes"? dirt/sand/small pieces of rock/silica? general material deterioration? something else?
 
Yes thats true . I had a snown blower with one metal reed . No start issue .
Found reed had bow in it , flipped it over so as to seal vroom vroom .
Wierd little setup had about a 5/16 hole for a port .
 
Hard to start them or not starting at all. I have experienced the engine sucking one piece. My fault for not replacing the reed when needed. Other than breaking they also tend to stop sealing or closing as they should.
 
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