Engine keeps backfiring under load motor is an enduro xl 13.5 hp
Need Make/Model/Year/Engine Model/Deck Size, and hours on meter if you have one. A short description of the events preceding the beginning of the problem is also helpful.
1. Needs a valve adjustment or a valve job. Start with adjustment.
2. Needs new plugs. Start with new plugs.
3. Shear pin under flywheel is slightly damaged throwing off the timing. Remove flywheel examine shear pin for any damage. Just go ahead and replace it; if it even looks nicked or sliced.
4. Coil, or spark plug wire, is going bad. Very hard to test a coil for weakness without test equipment that the average person doesn't have. Check the first 3 problems, first. If it still backfires, then replace coil.
5. The other thing that causes backfire is fuel mixture too lean. On a small engine this is not usually an adjustment problem. It may be the fuel system/carburetor is dirty or partially clogged. It may also be an air leak in the gaskets of the intake manifold. If nothing else solves the backfire, remove the carburetor and clean or rebuild it. This is the least likely of the options so save it for last.
If compression is good and cylinder leakage is minimal, but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery or ignition problem (fouled spark plug or bad plug wire). A power balance, or cylinder balance, test should be run on a twin cylinder engine.
If an engine is hard starting, runs rough, misses or lacks power, run a cylinder balance test to determine if both cylinders are operating to their full potential. You will need an engine tachometer, a spark tester, and an insulated screwdriver.
1. Using the spark tester, with the plugs in, start engine and verify spark is equally good on both cylinders. Remove spark tester.
2. Connect engine tachometer.
3. Run engine at top no load speed. Note rpm.
4. Ground one cylinder spark plug with screwdriver. Note rpm.
5. Ground other cylinder with screwdriver. Note rpm.
The difference in RPM between the cylinders should be less than 75 rpm. If the difference between the two cylinders is greater than 75 rpm, the cylinder with the least rpm loss is the weakest and is a potential problem.
Note: If the spark plugs are new this could be an indication of a weak coil. Of course it could also be compression (rings), or valves.
Mar 24, 2015 |