Anyone,

Is it necessary to remove the break in shim after one gallon ?
My first engine was running great with the shim. Fuel Bryon 30%
After I remove it, the engine seems to run hotter. And a little erratic on the tuning.
I put the shim back till now. It all goes back to as it was before.

Question; what does the shim do really ? Will there be a problem if I leave the shim on ?