by Skywatcher » Fri Nov 05, 2021 11:40 pm
Hi Again Dart
You mentioning that moving the throttle shaft either way doesn't make a difference. I've had three engines that behaved that way, each one for a different reason. The first was a virtical shaft Tecumseh on a JD 57 riding mower, the flywheel key had sheared and the crankshaft slipped in the flywheel retarding the timing to the point where the engine would not rev up.
The second was a B&S engine on a Coleman portable generator. The spark arrester in the muffler was completely plugged. If an engine can't breath out, it can't breath in and will spit back through the carburetor. Check for a loose baffle in the muffler restriction exhaust flow.
The third was a Kohler Command series engine on a Husqvarna lawn tractor. The intake lobe on the camshaft had worn down to the point where the intake valve was barely opening, so the engine was not getting a full charge of fuel/air mixture on the intake stroke.
Remove the muffler and try the engine again. If no change, remove the valve cover, rotate the engine by hand and see how far down the rockers are actually pushing the valves. If those both look good, remove the flywheel and check the condition of the flywheel key.
If the flywheel slips on the crankshaft as in the case of a lawnmower hitting a solid object, the engine will kick back when you're trying to start it. If the crankshaft slips within the flywheel due to flywheel nut not being properly torqued, the engine will be nice and easy to start, hut won't attain full RPM and the muffler will get unusually hot. Hope this gives you some ideas,
Sky
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