Echo HCA-265CS hedgetrimmers problem.

[Andy Collins]

Trimmer fires up ok, runs up to 3/4 revs ok and holds revs ok to that point. On full revs only, it develops a backfire, drop off revs and it's fine again. Sent it in for a tune -up and sort out, to be told it's knackered. I don't believe it is, but I can't put my brain into gear to think what it could be.

Ideas please?

[spudulike]

The back fire leads me to believe it may be the flywheel key has let loose or possibly the coil is shifting the ignition timing.

 

A back fire will occur when the ignition is very retarded or in laymans terms - when the piston is on the way down and not just before top dead centre. Excess fuel in the exhaust can also produce a bang or two.

 

I would pull the flywheel and inspect the key for starters. If the engine has compression and isn't knocking badly, it sounds like it has life left in it. Also check the exhaust hasn'tgot unburnt fuel in it.

 

Interesting one - be careful running it before checking the flywheel - ignition happening out of time can cause piston melt down!

Edited July 28, 2014 by spudulike

[GardenKit]

My money would be on the flywheel and coil too.

 

But it could be as simple as the spark plug, so I would change that first.

 

It could also be the coil breaking down internally.

 

Unless the guy who looked at is right and its knackered.

[spudulike]

My money would be on the flywheel and coil too.

 

But it could be as simple as the spark plug, so I would change that first.

 

It could also be the coil breaking down internally.

 

Unless the guy who looked at is right and its knackered.

 

Yes Barrie but there is "knackered! and "REALLY KNACKERED":sneaky2:

 

Just done a blower and it is totally FUBARed:thumbdown:

[Andy Collins]

Ok that's making sense so far. Will investigate further later. Quick question, key refers to Woodruff? Correct? The engine is not knocking, sounds "tight" still, the back fire only started the other day, resulting in me laying it up. I made the usual basic checks, change plug, clean fuel and filter, air filter, check leccy connections from switch, and the shop cleaned the carb ultrasonically. They didn't look at the woodruff or the timing to my knowledge.

Thanks both for your input.

[GardenKit]

You could try disconnecting the stop wires from the coil Andy. I had one years ago that shorted from one of the worn wires when the machine reached a cetain vibration. It ran fine disconnected, so proved the wires were at fault.

 

Obviously I must make the patronising disclaimer that you should not in fact use a machine with the wires disconected:biggrin:

[spudulike]

The flywheel key is in fact a woodruff key, the latter being the engineering term for the former and usually refers to the way gears are located on shafts:thumbup:

 

Some machines have small steel ones that insert in to the crankshaft (like Stihl), others have moulded keys actually on the flywheel - I have seen both shear in the past.

 

If you are very careful/lucky, you can realign the flywheel with the moulded key type on to the crank stub again - I have used a smear of JB weld and an inordinate amount of torque but it worked. Getting the timing 100% is key.....or just fit a new flywheel!

[jonnygurkha]

I have the same trimmer but my problem is on full revs it seems to go past the limiter and revs it’s nuts off. Dealer replaced a carb which sorted problem initially but now 4 months down the line same problem. Only happens irregularly. Any ideas?