[Richard and Rhonda]

Ok, here is the theory.

If you drill out the return restriction then your fuel pump actually circulates more fuel back to the tank, and in theory you will be sending cooler fuel to the injectors. Cooler fuel or cooler air means more power. That the good news. Now for the bad. I happen to know first hand where this very fitting is located on a Series 60 and what you have to do to get to it.

It is installed on the rear of the head. You have to remove the bedroom hatch, and be prepared to loosen and tighten three diesel fuel fittings to get it loose. They have to be done in a particular order because the fitting is L shaped and the whole L must be unthreaded from the head. You have fun with that.

There are all kinds of guys out there who are hot rodding DD engines. If you google around you will find enough info to make your head hurt.

I don't fret about mileage. It is a minuscule cost of owning any coach when you total depreciation and maintenance.

That pedal on the right. Stand on it.