I have a 15.5 HP OHV Briggs engine that was not revving up properly. It would take 5 seconds for it to go from an idle to full throttle. And full throttle wasn't as full as it should be. It was getting gas to the carb, the carb was very clean inside and it has a new air filter. So I went to adjust the valves thinking the intake valve may have been loose. I found that the exhaust valve rocker is moving properly but the intake rocker only moves in and out 1/4" or so. I do a lot of external work on mowers but have never torn an engine apart inside. Is there a cam that might be worn off? Or, do you expert know of something else that may be my trouble?

We just had one of these here with pictures and the CAM was essentially rounded off. Obvious problem.

Would be great if you could take it apart to verify and take some pics. But before buying parts talk to Briggs.