Acceptable Reed Gap

[reynome]

I was checking the reeds on my dad's 98 cr 250 and found that on the corner of his stock reeds there was a gap of about a penny's thickness. This was on both sides of the cage. There wasnt any chipping.

Is this enough to effect starting and low end?

I have since installed new reeds and they fit snug but was wondering how much gap is acceptable.

 

[spanky250]

No gap is acceptable. The reeds should close snuggly against the cage. When reeds lose their tension and cease to close completely, it's time for new ones.

 

[RM_guy]

There should be no gap at all. You could probably get away with .010" or so but any gap will allow fuel to be blown back into the carb.

You should notice that it is easier to start the bike now. A gap the size of a penny thickness is huge!

 

[David Trustrum]

Except that crankcase compression will close them, just as a ring is pushed against a bore by the compression & combustion pressure.

But if there is that much gap they are probably starting to delaminate or something.

I have a theory that reed performance can drop off with some materials after some time exposed to some gas, but it is anecdotal evidence that draws me to this conclusion.

 

[RM_guy]

Originally posted by David Trustrum
Except that crankcase compression will close them, ...

Yes, but when starting and at low rpm, they will leak before they totaly close.

 

[MikeT]

Zero. They should fit tight.

 

[reynome]

I guess at low rpm when the piston is coming down and causing positive pressure in the crank case the reeds will allow the charge to flow back into the carb before shutting. This makes even more sense when you think about starting the bike, this is when the positive pressure will be the lowest and have alot less tendicy to close the reeds.

Thanks for the replies, Im sure the new reeds will make a difference.

 

[David Trustrum]

Ahh kick it faster! :D

Seems some bikes are more susceptible than others. I had always been told/read that chipped/bad reeds would cause hard starting. One of my race bikes was giving me grief running crappy at the top end & I was chasing around all sorts of things trying to fix it.

When I got it home I decided to pull it down but found one of the (steel) reeds had broken off & there was a big gapping hole. Still started just fine though. Weird huh?