Help with Mcculloch 10-10 pulsing at full throttle

[Vanguard]

I haven't seen any posts about possible air leak. Did you check air filter, and if the choke plate on the carb isnt flapping on WOT? Check seals, hoses, etc. for any leaks?

Properly adjust your carb? YouTube has some good videos, check out Steve's Small Engine Salloon if you want to know how to really dial one in.

I recently fixed a buddies "homeowners" branded saw that had surging issues during WOT, just not quite as pronounced as yours. He had an air leak while the carb needed dialed in.

If the saw didn't pulsate during WOT before all the work you did, then it's a good chance something simple might be causing this issue.

 

[andrewsofia]

I haven't seen any posts about possible air leak. Did you check air filter, and if the choke plate on the carb isnt flapping on WOT? Check seals, hoses, etc. for any leaks?

Properly adjust your carb? YouTube has some good videos, check out Steve's Small Engine Salloon if you want to know how to really dial one in.

I recently fixed a buddies "homeowners" branded saw that had surging issues during WOT, just not quite as pronounced as yours. He had an air leak while the carb needed dialed in.

If the saw didn't pulsate during WOT before all the work you did, then it's a good chance something simple might be causing this issue.

Hi vanguard,

Air filter is good, fuel breather is good, i have adjusted carb multiple times as no change. Saw has always pulsed even previous owner tried to fix.

Gaskets between block and carbie was one thing I was going to add to list of inspection. But is not racing so leak would be on fuel pump side only if thatwas the case.

It has been a head scratcher

 

[RED-85-Z51]

Close the plug gap down to about 15thou...if it makes a difference that can tell us something.

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[SteveSr]

Close the plug gap down to about 15thou...if it makes a difference that can tell us something.

Sent from my LM-G820 using Tapatalk

Wouldn't hurt to change the plug too...

 

[andrewsofia]

Close the plug gap down to about 15thou...if it makes a difference that can tell us something.

Sent from my LM-G820 using Tapatalk

Red,

you are a legend, changed the gap to shorter and almost fully stabilizers RPM at WOT.
New spark plug actually made it worse.

So i am guess the coil is on way out and not able to proved required current? am i correct?

 

[Vintage Engine Repairs]

If you had the negative (black) wire in the 10a port for the testing, that’s not right. Move it to the COM port (one to the right) and re test.

 

[andrewsofia]

If you had the negative (black) wire in the 10a port for the testing, that’s not right. Move it to the COM port (one to the right) and re test.

I did that again this morning and recorded the same 13.3 on primary and 2.53 on secondary

 

[andrewsofia]

I did that again this morning and recorded the same 13.3 on primary and 2.53 on secondary

13.3 and 2530 is what I ment

 

[Vintage Engine Repairs]

13.3 and 2530 is what I ment

Seeing as primary is that high, confirm that the prongs on your ignition coil aren’t rusty / corroded, they need to be shiny metal. Same with your spark plug spring. Either way, those readings sound way out of spec. Especially as the primary specification is 0.6 - 0.9 ohms and you’re getting 13.3.

If some how, in the mac manual the 50-90 spec means 5k-9k I’d believe it and you are half of the resistance of the lower reading.

Can you please forward me the manual? I’ll take a look. I feel like I want to get to the bottom of this as much as you!

If your readings are correct, the coil wouldn’t be able to increase the voltage of current enough to give a consistently strong spark and I think it’s safe to assume, so long as you are certain you did the reading correctly, your ignition coil is failing.

Replace it and see how you go. Bring the plug gap back to 0.5mm.

Now you know how to rest a coil, when you look for a new one or new old stock you know how to test it. Bring your multimeter along with you when you collect it - test it before handing over money.

Learning what’s wrong is so important to avoid chasing your tail.

 

[RED-85-Z51]

Red,

you are a legend, changed the gap to shorter and almost fully stabilizers RPM at WOT.
New spark plug actually made it worse.

So i am guess the coil is on way out and not able to proved required current? am i correct?

Most likely. Its breaking up or blowing out the spark at higher rpms, it cant get enough saturation in the primary windings. Whenever i get a breakup like a limiter i close up the gap and if i see a notable improvement its a bad coil or points issue.

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[SteveSr]

Red,

you are a legend, changed the gap to shorter and almost fully stabilizers RPM at WOT.
New spark plug actually made it worse.

So i am guess the coil is on way out and not able to proved required current? am i correct?

Check the coil to magnet gap. This can also reduce the output if too large. You may also have a shorted turn or insulation failure on the secondary. I would start looking for a replacement coil. A meter is mostly useless checking coils except for shorts and opens.

If this is a points ignition you may also have a timing/gap or capacitor issue. This can also produce a weak spark.

 

[andrewsofia]

Check the coil to magnet gap. This can also reduce the output if too large. You may also have a shorted turn or insulation failure on the secondary. I would start looking for a replacement coil. A meter is mostly useless checking coils except for shorts and opens.

If this is a points ignition you may also have a timing/gap or capacitor issue. This can also produce a weak spark.

Luckily no points, I have had a few points saws

 

[andrewsofia]

Seeing as primary is that high, confirm that the prongs on your ignition coil aren’t rusty / corroded, they need to be shiny metal. Same with your spark plug spring. Either way, those readings sound way out of spec. Especially as the primary specification is 0.6 - 0.9 ohms and you’re getting 13.3.

If some how, in the mac manual the 50-90 spec means 5k-9k I’d believe it and you are half of the resistance of the lower reading.

Can you please forward me the manual? I’ll take a look. I feel like I want to get to the bottom of this as much as you!

If your readings are correct, the coil wouldn’t be able to increase the voltage of current enough to give a consistently strong spark and I think it’s safe to assume, so long as you are certain you did the reading correctly, your ignition coil is failing.

Replace it and see how you go. Bring the plug gap back to 0.5mm.

Now you know how to rest a coil, when you look for a new one or new old stock you know how to test it. Bring your multimeter along with you when you collect it - test it before handing over money.

Learning what’s wrong is so important to avoid chasing your tail.

I shall do that all tonight for you. I am grateful for all your help and everyones on here.

I am overwhelmed by the support and knowledge. Thank you

 

[SteveSr]

Luckily no points, I have had a few points saws

In that case any resistance readings other than HT lead to core is completely meaningless. It's an electronic coil!

 

[SteveSr]

Seeing as primary is that high, confirm that the prongs on your ignition coil aren’t rusty / corroded, they need to be shiny metal. Same with your spark plug spring. Either way, those readings sound way out of spec. Especially as the primary specification is 0.6 - 0.9 ohms and you’re getting 13.3.

If some how, in the mac manual the 50-90 spec means 5k-9k I’d believe it and you are half of the resistance of the lower reading.

Can you please forward me the manual? I’ll take a look. I feel like I want to get to the bottom of this as much as you!

If your readings are correct, the coil wouldn’t be able to increase the voltage of current enough to give a consistently strong spark and I think it’s safe to assume, so long as you are certain you did the reading correctly, your ignition coil is failing.

Replace it and see how you go. Bring the plug gap back to 0.5mm.

Now you know how to rest a coil, when you look for a new one or new old stock you know how to test it. Bring your multimeter along with you when you collect it - test it before handing over money.

Learning what’s wrong is so important to avoid chasing your tail.

Sorry, This is an electronic coil the actual primary wire is inaccessible. All you have access to is the kill wire which disappears into the electronic switch circuitry. It is NOT connected to the primary. Any resistance reading is meaningless.

 

[RED-85-Z51]

This is why i don't test coils with a meter...ive had good coils test bad, bad coils test good.

If closing the gap improves it, replace the coil..problem solved.

Sent from my LM-G820 using Tapatalk

 

[Vintage Engine Repairs]

Sorry I deleted my other post, Steve is right, if it’s from an ELECTRONIC ignition and NOT points then it has to go through an ignition module. These should be put on different tester, which energises the coil. It’s not reliant of on resistance readings. Your local dealer may have one, but it’a not something you’ll have access to at home.

 

[andrewsofia]

Sorry I deleted my other post, Steve is right, if it’s from an ELECTRONIC ignition and NOT points then it has to go through an ignition module. These should be put on different tester, which energises the coil and tests the strength. It’s not reliant of on resistance readings. Your local dealer may have one, but it’a not something you’ll have access to at home.

Thank you both for info, it is much appreciated. Spark plug gap might have been issue as was larger than 0.5mm before. But might get a new good one and test. Also sourcing replacement coil as well just incase.

 

[Vintage Engine Repairs]

Thank you both for info, it is much appreciated. Spark plug gap might have been issue as was larger than 0.5mm before. But might get a new good one and test. Also sourcing replacement coil as well just incase.

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.

 

[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.

Will make video tomorrow as too late here at my place to make that much noise .... neighbours will kill me!!