Help with Mcculloch 10-10 pulsing at full throttle

[andrewsofia]

Hi,
This is my first post on this site and first chainsaw post ever.
I have a 10-10 that is very clean however it does a weird thing at full throttle i can not diagnose.
When you pin the throttle to max, it pulses revs from 60% to 100% and back again. (here is a vid: ) 10-10 vid
Things i have done to date:
- New fuel line
- New fuel filter
- Full carb rebuild
- Checked fuel breather line.
- Sprayed carb cleaner while idling to see if change in rpm

any help would be amazing.

Andrew (Sunshine Coast, Australia)

 

[Vintage Engine Repairs]

Hey from WA, thats nothing to do with a lean symptom - it’s not fuel related, that is a spark issue.

I had exactly that on my 07. Has yours been converted from points to electronic ignition? This was very commonly done in the late 70’s - 80’s.

look for a brown Atom chip:



How many magnets are on the flywheel?

Grab a tachometer and see if it is double sparking. Example, if that model should only run to 9,000 rpm is it saying 18,000? Or idle if there is no chain engagement but the tach is saying 4-6000 rpm.
While you’re in there if there is no chip, test the capacitor and the primary and secondary windings with a multi meter. Also check the condition of the points, that they are gapped properly and are breaking cleanly and timed correctly.

Grab a service manual from “the beg for manual” thread in the chainsaw sub forum.

 

[andrewsofia]

Hey from WA, thats nothing to do with a lean symptom - it’s not fuel related, that is a spark issue.

I had exactly that on my 07. Has yours been converted from points to electronic ignition? This was very commonly done in the late 70’s - 80’s.

look for a brown Atom chip:

View attachment 886530

How many magnets are on the flywheel?

Grab a tachometer and see if it is double sparking. Example, if that model should only run to 9,000 rpm is it saying 18,000?


While you’re in there if there is no chip, test the capacitor and the primary and secondary windings with a multi meter. Also check the condition of the points, that they are gapped properly and are breaking cleanly and timed correctly.

Grab a service manual from “the beg for manual” thread in the chainsaw sub forum.

Hi Gaudaost,

It is electronic ignition not points luckily with 2 magnets next to each other.
I have gapped it to 0.15inch gap and fixed the plug as well due to it being pulled apart (removed boot, trimmed and reset)
Can you replace the whole spark plug line without changing the coil?

Thanks for the help

 

[RED-85-Z51]

Thats definitely ignition cutting out like a rev limiter...

Sent from my LM-G820 using Tapatalk

 

[andrewsofia]

Thats definitely ignition cutting out like a rev limiter...

Sent from my LM-G820 using Tapatalk

Hi Red-85-Z51,

Thank you, so you would recommend replacing coil or flywheel or both?
Or is there a way if testing coils for this issue?

 

[Vintage Engine Repairs]

Slow down don’t start randomly replacing parts through guessing. Take the methodical approach and test things first.

First test the primary and secondary windings.

The instructions will be in the service manual.

 

[andrewsofia]

Slow down don’t start randomly replacing parts through guessing. Take the methodical approach and test things first.

First test the primary and secondary windings.

The instructions will be in the service manual.

 

[trains]

If its the original coil, I would suggest trying to richen the H a 1/4, then 1/2 a turn and see if it clears it up a bit, that would rule out the ball valve in the carb causing issues, and a basic carb setting not being quite right, you didnt mention where you set the carb screws.

Rule that out, its quick and easy to do, then look at the coil as already mentioned.

 

[andrewsofia]

If its the original coil, I would suggest trying to richen the H a 1/4, then 1/2 a turn and see if it clears it up a bit, that would rule out the ball valve in the carb causing issues, and a basic carb setting not being quite right, you didnt mention where you set the carb screws.

Rule that out, its quick and easy to do, then look at the coil as already mentioned.

Hi,
Originally I set carb to 1.5 low and 1.25high. I have moved high up and up but does not make much change last time

 

[andrewsofia]

Coil tests

 

[Vintage Engine Repairs]

Typically and this is fairly broad. Primary should read 1-2 ohms of resistance and secondary should read 5k-6k ohms. Though on a couple of saws the secondary windings have given considerably higher readings and been just fine.

First test (primary) should be one probe to ground and the other to negative (the polarity is irrelevant) somewhere around 1-2ohms

Second test is one prong to ground (or negative, doesn’t matter) the other to the spring at the end of the HT and that should be 5k-6k ohms. Again you’ll need a manual to confirm the above resistances for your specific model, but that’s a ball park figure.

 

[Vintage Engine Repairs]

Hope this helps, re test your coil with the following tutorial video I recorded for you and share the info you get -

when testing primary set to “200” setting

when testing secondary set to “20k”

 

[andrewsofia]

Hope this helps, re test your coil with the following tutorial video I recorded for you and share the info you get -

when testing primary set to “200” setting

when testing secondary set to “20k”

Thank you so much ... very helpful

 

[andrewsofia]

Hope this helps, re test your coil with the following tutorial video I recorded for you and share the info you get -

when testing primary set to “200” setting

when testing secondary set to “20k”

Primary: 13.3 (200 setting)
Secondary: 2.53 (20k setting)

 

[Vintage Engine Repairs]

Primary: 13.3 (200 setting)
Secondary: 2.53 (20k setting)

Primary at 13.3 ohms seems way high and secondary at 2530 ohms seems far too low. This could be the reason you’re not getting sufficient spark / charge that’s demanded at WOT.

None the less, let’s not just jump to conclusions without having the specs from the manual.

So, click this link and request -

“a service manual and IPL for the Mac 10 10”

https://www.arboristsite.com/community/threads/the-beg-for-manuals-thread.68615/page-1657
Ray or one of the other chaps will send it to your inbox. Download both but for now just open the service manual and on the first few pages it will have the specifications for the resistance for primary and secondary windings, likly under a main heading of “ignition system”

Then come back here and quote them to us

 

[andrewsofia]

Primary at 13.3 ohms seems way high and secondary at 2530 ohms seems far too low. This could be the reason you’re not getting sufficient spark / charge that’s demanded at WOT.

None the less, let’s not just jump to conclusions without having the specs from the manual.

So, click this link and request -

“a service manual and IPL for the Mac 10 10”

https://www.arboristsite.com/community/threads/the-beg-for-manuals-thread.68615/page-1657
Ray or one of the other chaps will send it to your inbox. Download both but for now just open the service manual and on the first few pages it will have the specifications for the resistance for primary and secondary windings, likly under a main heading of “ignition system”

Then come back here and quote them to us

Thank you so much for all assistance

 

[SteveSr]

Coil tests

What are you trying to measure in that second photo? The leads are plugged into the meter wrong.

Also keep in mind that resistance measurements will NOT tell you if there is insulation breakdown in the windings.

Does this carb have a "ball" speed limiter on it? If so did you clean and flush the spring area behind the ball? Is it possible to temporarily bypass this thing with some teflon tape or similar?

 

[andrewsofia]

What are you trying to measure in that second photo? The leads are plugged into the meter wrong.

Also keep in mind that resistance measurements will NOT tell you if there is insulation breakdown in the windings.

Does this carb have a "ball" speed limiter on it? If so did you clean and flush the spring area behind the ball? Is it possible to temporarily bypass this thing with some teflon tape or similar?

The carb is a Walbro SDC carb, never heard of a ball speed limiter in the carbs i have worked on (mind you they are normally earlier models).
Where would i locate this ball if it existed?

 

[andrewsofia]

Primary at 13.3 ohms seems way high and secondary at 2530 ohms seems far too low. This could be the reason you’re not getting sufficient spark / charge that’s demanded at WOT.

None the less, let’s not just jump to conclusions without having the specs from the manual.

So, click this link and request -

“a service manual and IPL for the Mac 10 10”

https://www.arboristsite.com/community/threads/the-beg-for-manuals-thread.68615/page-1657
Ray or one of the other chaps will send it to your inbox. Download both but for now just open the service manual and on the first few pages it will have the specifications for the resistance for primary and secondary windings, likly under a main heading of “ignition system”

Then come back here and quote them to us

 

[SteveSr]

The carb is a Walbro SDC carb, never heard of a ball speed limiter in the carbs i have worked on (mind you they are normally earlier models).
Where would i locate this ball if it existed?

Yes, it does. It is #15 in the attached drawing. At a certain engine speed/vibration the ball opens and dumps fuel into the engine limiting the speed.