This topic is all over the place. Data Points:
- A thread on this forum for Tillotson HW27 rebuild intervals contains posts which advise (A) new gaskets every 3-4 hours, (B) only when doing bottom end (every 30 hours or so), (C) pop-off every 3-4 hours and only service if outside of 8 to 12 psi, (D) and Tillotson its-own-self which says to replace the diaphragms and gaskets after every race “weekend” or after 2-4 “casual use” races (anyone do that???). And only replace needle and seat if damaged or once a season.
- VLR manual, page 16, calls for carb cleaning every day. Cleaning means to take off carb and do a pop-off test. If “OK”, put back on and race.
- KA manual (MUCH better and more detailed than VLR manual) doesn’t even reference carb at all in maintenance section page 30, and only mentions replacing carb parts in trouble shooting section page 31 IF engine won’t start.
- My distributor wanted to push a VLR 100 to test reliability. He has over 100 hours on the engine and has never done anything except replace a starter component, a cracked reed valve, and one spark plug. Neither the engine nor the carb has been disassembled. Ever. And the engine is running fast.
So, my questions. Ignoring the variety of intervals from above, can anyone explain WHY we would replace the diaphragms and gaskets? In other words, other than obviously torn or damaged parts, the only thing I’ve seen anywhere is a reference to “sagging” parts. What does this mean? How is it measured? How does it impact performance? And, as to the needle and seat, is the only measure of their functionality a pop-off range outside of 8-12 psi? And does this mean that the needle is sticking or leaking around the seat? Or something else that is above my pay grade?