Weak Sparks

[DaveyCrockett]

I'm working on an old Stihl 034 AV electronic quickstop. I have had it fire on direct priming with carb cleaner but not at all reliably. Sparks well over 0.5 mm gapped plug out the cylinder but can't jump a 3 mm gap.

 

In my experience ignition modules fail totally or when they get hot so I'm thinking weak magnets in the flywheel. What do people think is my best move? Is is worthwhile taking a punt on a second-hand flywheel? A new one is about £95. Should I buy a pattern module just to get it eliminated? Does anyone know how to test the magnet strength or get them re-magnetised?

 

Thanks for any advice.

[Stubby]

I'm working on an old Stihl 034 AV electronic quickstop. I have had it fire on direct priming with carb cleaner but not at all reliably. Sparks well over 0.5 mm gapped plug out the cylinder but can't jump a 3 mm gap.

 

In my experience ignition modules fail totally or when they get hot so I'm thinking weak magnets in the flywheel. What do people think is my best move? Is is worthwhile taking a punt on a second-hand flywheel? A new one is about £95. Should I buy a pattern module just to get it eliminated? Does anyone know how to test the magnet strength or get them re-magnetised?

 

Thanks for any advice.

 

Check the flywheel magnet to ignition unit gap first . As Spud would say a business card thickness is about right .

[DaveyCrockett]

That's already done Stubby, but I haven't checked the grounding on the module so I'll clean everything up, reset gap and try again.

[spudulike]

Try closing the gap down a bit and see if it helps. Not worth changing anything unless it fails completely!

[DaveyCrockett]

This problem is fixed now so I thought I would tell you the outcome.

 

I decided to buy a coil (ignition module) as this was the cheaper option, but thought I would check out the coil resistance first. I found that the HT lead was open but the resistance from the HT screw to ground to the was 7.6 kohm.

 

I replaced the HT lead expecting it to run, but no.

 

I bought a pattern coil, and it was a pretty bad fit. I had to shorten the HT screw and plastic surround where the lead comes out, but eventually got it in.

 

The spark jumped 3 mm (orange looking spark) but saw runs OK. It looks like the flywheel magnets are good after all.

 

Thanks for you help, Dave

Edited April 28, 2017 by DaveyCrockett
clarificaton