73X8 reed valves:how to diagnose?

[kiedro44]

My 73x8 runs good up to about half throttle, then flatlines out at about 25mph. No top end performance. Adjusting carb has not helped, cage and reeds look clean behind the carb. There is some spit back out the carb at higher RPMs. Compression is at about 135 per cylinder after three revolutions. How can you tell if the reed valves are bad, and is this really a common problem? I'm suspecting the Walbro here, but don't want to jump to conclusions. Any help is appreciated.

[JD600]

Your problems could also bein the electrical side of things. Have you replaced your crank seals? Leaky can cause all sorts of weird problems, as well as melt pistons.

DE

[kiedro44]

Thanks for the reply.
If the motor holds good compression, wouldn't that indicate the crank seals are good?

[400brian]

No, compression and seal condition are two different things. To test seal condition you have to pressure test the engine case. Your time is better spent in just replacing the seals, being as they are probably 37 years old.
Reeds do not seem to be a big problem, I'd look elsewhere for problems unless they are obviously damaged or nonfunctional.

[kiedro44]

I see what you mean. I was just reading a 73 JD service manual online that describes how to do the case pressure test. The reeds look good anyway. I'll invest in case seals.
Just in case anyone else is looking for factory tech info like the service manual I mentioned, that PDF, along with a lot of other JD info, is at
http://www.vintagesnow.com/John_Deere.html

Thanks.