Curious 1979 Q-jet Problem

[cowboy5683]

I have a 1979 qjet that has been rebuilt ( I did it)..It runs perfect. No leaks stalls or stutters..Here is the weird part..When sitting for awhile (mebbe a week at most) I can look under the hood and cleaner and all the vacuum caps I have used are cracking..I have replaced them twice and yet they still crack within a week..I am thinking mebbe my float level is a tad too high?!?..Mebbe some of you know for sure..I have dealt with and rebuilt qjets for years and never seen this before..what do ya'll think?..I will prolly reset level lower anyways..But just thought i would pick ya'lls brains first.