Hedge Trimmer stalls, backfires then won’t start again!

[spudulike]

If you are using 25:1 mix with an oil specified to be mixed 50:1 it will smoke, cover the engine internals with more carbon and the oil will deposit inside the exhaust and will generally foul the engine/plug unless it is worked at full heat and revs but even then, at best you will just produce more carbon.

The comment you use "running lean" is generally used in relation to the AIR and FUEL (Fuel =petrol + oil) entering the engine. If you mix lots of oil in with your petrol, your FUEL to AIR mixture will stay the same (assuming the viscosity of the fuel isn't significantly affected) but you will be burning more oil and less petrol so is this technically running lean?......not really because in two strokes, "running lean" is normally used in conjunction with the engine over revving and thus overheating and seizing as the piston overheats and melts on the exhaust (hot) side.

If you use too much oil, the engine will not seize, over rev or overheat but it will carbon up, foul the muffler/plug with unburnt oil and in extreme cases, will stop the engine revving out as it should.

A mix of 50:1 or perhaps 45:1 if using modified kit is sufficient. 25:1 dates back to a time where the oils were not as advanced as they are now.

The only time I have known machines to back fire is either on starting - mostly the 372XPT saw and assume that the coil has a very retarded start circuit and the other time are ignition issues and more often or not, it is a sign the flywheel key has failed and the ignition timing is that retarded, the ignition happens far too late causing the fuel in the muffler to ignite and backfire.

Yours starts and runs for a period so it is very unlikely that this has failed.

The fact it runs for a period, back fires and then starts again when colder leads me to believe that the coil heats up as coils do when you put a charge through them and this is making it fail - your coil may have a separate spark unit as explained earlier, it is possible that either this is failing under the heat of use or the connections are faulty.

With ignition issues it is always worth changing the plug for a new one as people drop them causing unseen damage and it is always worth checking the HT lead and spur connector in the cap with a multimeter for continuity but beyond the "easy to do" options, the issues will be ignition linked.

But ADW and I may be wrong!

[fieldscience]

Thank you for such a comprehensive reply. I think I will give it to an expert to sort out though as that sounds out of my skill set! Thanks again. 

[spudulike]

If you are in South Devon, try "Gardenkit", he is a member on this forum and is one of the few people I know and would recommend in your area - Near Sidmouth! He is a typical "Old School" mechanic/engineer so should be able to assist.

east devon garden machinery | Garden Machinery Repairs

WWW.GARDEN-KIT.CO.UK

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For all your new east devon garden machinery needs, from tractors to mowers and brush cutters. We can also service and repair your machines when they let you down, as well as...

 

[adw]

You mind he doesn't try and sell you a hundred gallons of Aspen fuel.

[spudulike]

9 hours ago, adw said:

You mind he doesn't try and sell you a hundred gallons of Aspen fuel.

Bit harsh old boy