There is no real “too often” frequency for using Berryman Intake Valve & Combustion Chamber Cleaner (part #2611).  During the development of this product, it was not uncommon for our team to use 6 cans of product on the same vehicle in a single afternoon.  If you feel like you have a severe carbon buildup problem in the combustion chambers, you can safely run multiple cans back-to-back.  If you choose to go this route, consider the purchase of a case of 2611-PRO in order to save money through the elimination of display cartons and several application accessories kits.   You can also try using a detergent-based fuel additive either with or without using additional cans of 2611.  In that case, we would recommend either Berryman B-60 High-Mileage Fuel System Rejuvenator (part #7516) or B-12 Chemtool Total Fuel System Clean-Up (part #2616).  Both products contain our best detergent-based package will address carbon buildup in the combustion chambers and, as a bonus, will clean fuel injectors and PFI intake valves.