Bahmi 5 #1 Posted July 25, 2017 I ran and mowed with my new, to me, 312-8 today. Went about 20 minutes. Engine was then shut down for 15 minutes. Tried to start it again, nothing happened. Nothing. Is this characteristic of some well known problem with the engine or carburetor? Where do I start to diagnose this quirk? thanks Just now, Bahmi said: I ran and mowed with my new, to me, 312-8 today. Went about 20 minutes. Engine was then shut down for 15 minutes. Tried to start it again, nothing happened. Nothing. Is this characteristic of some well known problem with the engine or carburetor? Where do I start to diagnose this quirk? thanks While running, the engine at higher speeds and while just sitting still, was searching. Run, search, run, search. No adjustment seemed to make any difference. Share this post Link to post Share on other sites
953 nut 58,164 #2 Posted July 25, 2017 I would start by replacing the spark plug, air filter, fuel line and fuel filter. Use non-ethanol fuel (ethanol will crap up the fuel system) and add Seafoam fuel additive to clean the fuel system. Lots of problems are the result of deferred maintenance. 1 Share this post Link to post Share on other sites
squonk 42,720 #3 Posted July 25, 2017 With the searching issue, check for slop in the throttle shaft where it passes thru the top of the carb. The cable pulling sideways on the throttle will cause it to wear into the carb body causing an air leak. 3 Share this post Link to post Share on other sites
prondzy 3,883 #4 Posted July 31, 2017 I have had 2 magnum 12s with bad fuel pumps, the plastic pumps have a felt like material used for the check valve seats i beleive. This material breaks up and lodges in the check valves holding them open or shut giving you a no start condition. Try swapping with a known good fuel pump. A metal one from a K series will work just make sure you get the arm on the top side of the camshaft lobe. Share this post Link to post Share on other sites
wfrpalm 218 #5 Posted July 31, 2017 When you say nothing happened do you mean it would not turn over or would not start? Share this post Link to post Share on other sites