Help with Mcculloch 10-10 pulsing at full throttle

[Maintenance supervisor]

Kill switch wire under the handle has come loose on me once or twice.
The lead wire to the plug likes to rub on the block cover, people have pulled the spring loose under the plug boot loose placing their foot on the lead when starting? Go simple first .
When running run your hand up a down the length of the lead ,it'll bite you if its broke. Flashlight assistance for seeing the tiny screw under the trigger for the kill switch, and pull the boot back to check the other.
Last join the McCulloch thread.

 

[andrewsofia]

There should be specs for the plug gap, but typically it’s 0.5mm

At 0.5mm do you get a smooth runnning saw?

Do upload another video.

Here is vid you asked ... gapped at about 0.5mm with feeler gauge.

 

[andrewsofia]

Can you replace just the spark plug lead without replacing the whole coil? One thing I noticed yesterday is I got a boot from lead when hand accidentally touched it. But lead cover feels good with no noticeable breaks.

 

[Vintage Engine Repairs]

Sounds better! I still think your 2.5k ohms is low for a secondary reading so keep an eye out for a NOS replacement from the USA, but if it’s running smoothly at WOT enjoy it until it no longer works.

As for the wire, what does your manual say? That will tell you if they are replaceable. I have replaced a few on Stihl saws and they just unscrew off the threads, screw a new lead back on and replace the boot.

 

[SteveSr]

Can you replace just the spark plug lead without replacing the whole coil? One thing I noticed yesterday is I got a boot from lead when hand accidentally touched it. But lead cover feels good with no noticeable breaks.

Look for glue or potting compound where the HT lead enters the coil. If you find it it means that the lead is not replaceable. Most replaceable ones have a rubber cover boot and the wire screws in.

You ahould NOT have gotten bit by getting close to the insulated spark plug boot unless it is compromised. The painless way to find insulation breakdown is with an insulated screwdriver and a lead wire from the metal screwdriver to chassis. Then while the saw is running, turn out the lights and position the screwdriver near the lead wire and spark plug boot and look for sparks jumping.

 

[Woodslasher]

Look for glue or potting compound where the HT lead enters the coil. If you find it it means that the lead is not replaceable. Most replaceable ones have a rubber cover boot and the wire screws in.

You should NOT have gotten bit by getting close to the insulated spark plug boot unless it is compromised. The painless way to find insulation breakdown is with an insulated screwdriver and a lead wire from the metal screwdriver to chassis. Then while the saw is running, turn out the lights and position the screwdriver near the lead wire and spark plug boot and look for sparks jumping.

I replaced a glued-in wire on a RH 10-10, I pulled the wire out of the coil body, picked the many remaining little rubber bits out of the hole, shoved the new wire in and that was it! I bought the Proline 5mm "041 Stihl Plug Wire" kit, which was plenty long and the right diameter.

 

[andrewsofia]

Sounds better! I still think your 2.5k ohms is low for a secondary reading so keep an eye out for a NOS replacement from the USA, but if it’s running smoothly at WOT enjoy it until it no longer works.

As for the wire, what does your manual say? That will tell you if they are replaceable. I have replaced a few on Stihl saws and they just unscrew off the threads, screw a new lead back on and replace the boot.

Thanks,
Yep have ordered a replacement for my 600014U model.

https://www.ebay.com.au/itm/OEM-McC...-/113634183315?_trksid=p2349624.m46890.l49292
I have already spent a few dollars on lines and other pieces so might as well get it perfect and keep in good condition.

Thanks for assistance.

 

[andrewsofia]

Look for glue or potting compound where the HT lead enters the coil. If you find it it means that the lead is not replaceable. Most replaceable ones have a rubber cover boot and the wire screws in.

You ahould NOT have gotten bit by getting close to the insulated spark plug boot unless it is compromised. The painless way to find insulation breakdown is with an insulated screwdriver and a lead wire from the metal screwdriver to chassis. Then while the saw is running, turn out the lights and position the screwdriver near the lead wire and spark plug boot and look for sparks jumping.

Will give this a try ... brought spare just encase but would be good to keep original.

 

[andrewsofia]

I would like to say again a massive thank you for all your assistance and knowledge. I am a software engineer by profession so all this has been a massive learning curve. This would be the 35th saw I have fixed but definitely the most complex issue to diagnose and resolve (most have been early 2000 mccullochs). I an amazed at the warmth displayed by all I have talked to in this chainsaw community with regards to assistance and wisdom. So just wanted to say thank you again.

 

[Maintenance supervisor]

The McCulloch community is a good one.
Fyi there's a tiny post, inside the socket that holds the lead wire in, so not only is it glued but threaded in place ,must twist when removing.

 

[andrewsofia]

The McCulloch community is a good one.
Fyi there's a tiny post, inside the socket that holds the lead wire in, so not only is it glued but threaded in place ,must twist when removing.

Clockwise or counter clockwise twist?

 

[Goinwheelin]

Clockwise or counter clockwise twist?

Righty tighty lefty loosie. Dab of silicone or other sealant helps when re installing the wire.

 

[djones]

I have run into the bad plug wire problem several times and have replaced them on many McCullochs. If glued in place, a Dremel tool with a fine drill bit or shaping bit will work to get along the edge of the post where the wire goes in. Clean it out down to the bottom and as mentioned above twist the wire out of the post. Using a piece of wire core spark plug wire, twist it into place and mark with a pen on the wire the point where the wire meets the coil post. Remove the wire and place epoxy on the wire up to that pen mark and reinstall into the coil with a twisting motion. Allow to dry. Cut the wire to length, install wire coil for the spark plug and then the spark plug boot. A rubber grommet in the metal housing where the plug wire goes through will also prevent further shorting of the wire in that area. Good luck and hope this helps.

 

[SteveSr]

I have run into the bad plug wire problem several times and have replaced them on many McCullochs. If glued in place, a Dremel tool with a fine drill bit or shaping bit will work to get along the edge of the post where the wire goes in. Clean it out down to the bottom and as mentioned above twist the wire out of the post. Using a piece of wire core spark plug wire, twist it into place and mark with a pen on the wire the point where the wire meets the coil post. Remove the wire and place epoxy on the wire up to that pen mark and reinstall into the coil with a twisting motion. Allow to dry. Cut the wire to length, install wire coil for the spark plug and then the spark plug boot. A rubber grommet in the metal housing where the plug wire goes through will also prevent further shorting of the wire in that area. Good luck and hope this helps.

For everyone who mentions gluing in the wire... what happens when you have to replace the wire again?

 

[Goinwheelin]

For everyone who mentions gluing in the wire... what happens when you have to replace the wire again?

Use new glue

 

[SteveSr]

Use new glue

For those with without disassembly experience maybe I should have been more specific, If you glue it together too well you may destroy it next time. A little bit of clear RTV around the coil tower is all I would use. Certainly not epoxy all the way down into the coil.

 

[Goinwheelin]

For those with without disassembly experience maybe I should have been more specific, If you glue it together too well you may destroy it next time. A little bit of clear RTV around the coil tower is all I would use. Certainly not epoxy all the way down into the coil.

That’s why I use silicone

 

[andrewsofia]

I have run into the bad plug wire problem several times and have replaced them on many McCullochs. If glued in place, a Dremel tool with a fine drill bit or shaping bit will work to get along the edge of the post where the wire goes in. Clean it out down to the bottom and as mentioned above twist the wire out of the post. Using a piece of wire core spark plug wire, twist it into place and mark with a pen on the wire the point where the wire meets the coil post. Remove the wire and place epoxy on the wire up to that pen mark and reinstall into the coil with a twisting motion. Allow to dry. Cut the wire to length, install wire coil for the spark plug and then the spark plug boot. A rubber grommet in the metal housing where the plug wire goes through will also prevent further shorting of the wire in that area. Good luck and hope this helps.

Thank you, yeah ordered some 7mm HT cable today and will try repair seeing I have a spare coming anyway.

 

[Goinwheelin]

Also just a cursory re read of this thread didn’t net any evidence that someone recommended epoxy on the wire

 

[trains]

Couple of points.

You mentioned that you got bit by spark when your hands were near the wire/ plug boot.
Electricity is lazy, so it will take the easiest option.
when your hand was there, it took that path instead of going across the plug gap.
You said the plug gap was quite wide, and you narrowed it, then it ran better.
so now the plug gap is the easiest route for the spark, and not thru the wire/ insulator area.

my assumption would be that due to poor wire/ boot insulation, and allowing an easier path for the spark to ground before it reached and jumped the spark plug, would have given you the original poor running.

Find where the breakdown of wire/ boot insulation is with the above methods, or if you want frizzy hair, use your fingers to find the bite area.

Coil may be fine in the end, just that there is an easier path for the electrickery to follow due to poor insulation somewhere along the line.

With how its running now, if you put it under load in the cut, that will put the spark to the test again, as higher cyllinder pressure, ie wide open throttle, will make it harder for the spark to jump across the gap.

if you can do that in the dark, or low light, you might see where the stray current / short is going.

Edited to add.
just realised a whole lot of posts before covered this, but they didnt show up when I last viewed the post and replied.