RJR49 138 #1 Posted May 21, 2021 When mowing up a fairly steep hill I was getting a pretty severe knock if I didn't back off the throttle. After I replaced the mechanical pump with an electric one the knock disappeared! I didn't change the points, which were set at .020, and am wondering if there is an explanation Share this post Link to post Share on other sites
lynnmor 7,815 #2 Posted May 21, 2021 If you had a mechanical fuel pump, then maybe is was making noise. If it was a detonation type of knock, then the mixture may have gone lean because the fuel pump couldn't quite keep up. 2 Share this post Link to post Share on other sites
squonk 43,799 #3 Posted May 21, 2021 Lean mixture is more prone to pre-ignition. 1 Share this post Link to post Share on other sites
RJR49 138 #4 Posted May 21, 2021 Do you think the pump was getting tired? There wasn't any sign of fuel in the oil so I figured it was pumping ok Share this post Link to post Share on other sites
953 nut 59,924 #5 Posted May 21, 2021 There are two check valves in the mechanical fuel pump. If these valve leak by you could be staving the engine under a heavy load. Electric is the way to go 1 Share this post Link to post Share on other sites
tunahead72 2,543 #6 Posted July 3, 2021 Any updates @RJR49 ? Is the knock still gone with the new electric pump? Share this post Link to post Share on other sites
