Mc101 reed damage

[philrock]

The reeds in my Mc101 are getting badly chipped for some reason. I understand this is not unusual, but the last set of reeds lasted less than an hour. The second photo below is an old reed that lasted a number of hours - seemed reasonable to me. This reed was .023" thick.

The first and last photos show a replacement reed of a different design and thickness. The corners are more squared off and the thickness is .013". At first, the outside squared off corners hung out over the edge of the reed cage. I dressed the outside corners down so they did not overhang before I tightened down the reeds and ran the engine.

As you can see, one of the new reeds is just slightly chipped, and the other is really disintegrating. I don't imagine the chunks of reed have done anything good to the inside of the engine.

91 octane pump gas
Blendzall 460 oil
16:1 mix
HL-334AB carb
rpms never get over 12,200

Any ideas what the problem is here?

I've heard of reeds called "snakeskin." Are these any good?

[Sonny Gerber]

The first thing that comes to my mind is that you may have one of the early stock manifolds that allows the reeds to set deeper than later ones. Look at your manifold, you want the one that has a raised "H" cast in it . The earlier ones lead to the problem you describe.

Your explanation of the edge treatment of the reeds seems right on. I use 800 to 1000 grit sandpaper to dress the edges and that seems to give longer life.

Lastly, I've always had the best experience with genuine McCulloch reeds, particularly the darker colored ones.

Remember, free advice is sometimes worth what you paid for it, and I could well be wrong....Sonny

[mcbob]

Are those reeds shown the origional type of Mac reed this will prove to be an interesting read i believe the white type of reed i cannot recall its name is better material ............ but what i have said is it true ?

McBob

[philrock]

My manifold has the "H" cast in.

I believe the reed with the fully rounded ends is the original type.

When I dressed the new reeds, I only used 400 grit emery paper. Makes sense that 800 or 1000 grit would be better.

Are steel reeds ever used on these engines?

[steveohara]

Phil,

Listen to Sonny, he is right on about the manifold and the OEM Mac reeds but those rules evolved in engines fitted OEM carbs and reed cages.

You will also need to look at a couple other things that may be causing your reeds to fail quicker than normal.
One is the metal reed guards.... if the arc has been modified that can lead to reed problems so check to see if you are running stock guards or if they have been altered.
Second, you are running an adapter plate to let you mount the Tilly carb that changes the overall length of the intake tract and that could be a contributor as well.
The intake systems are very sensative to changes in length, throttle bore, reed guard shape, reed strength etc.
Since you are running a different carb and intake manifold length you will have to experiment with different reed materials and guard shapes to find a combination that gives good performance and reed life.
Have fun!
Steve O'Hara