Husqvarna Timing Curves

[Ozhoo]

With all the discussion recently on timing, I thought I'd do a little research to unravel what these mysterious little black boxes are actually doing.

Current XP models use either a SEM AM50 or a SEMAM50COT. Here's the timing curves for those two.

AM50



AM50COT


Husqvarna (Current) Model Specs

O

 

[w8ye]

Essentially the curve is just to get it started without kick back?

 

[Ozhoo]

SEM AM33's are used on lots of older models. It doesn't get much flatter than this.



While others use a SEM AM7


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[Ozhoo]

Essentially the curve is just to get it started without kick back?

Exactly... these are all analog modules so there's no programmable controls.

O

 

[Ozhoo]

Walbro MB's are used on several models and while I can't find individual timing curves for those, they're similar to the AM50.
Walbro Ignition Modules (PDF)

SEM Ignition Modules

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[Chris-PA]

Interesting that the SEM AM7 is so different - it's less advance and not all in until over 7000rpm. What is that used on?

 

[Ozhoo]

Interesting that the SEM AM7 is so different - it's less advance and not all in until over 7000rpm. What is that used on?

Agreed. It's spec'd on the 181 and 42/242. I'm sure there are others as well.

O

 

[MustangMike]

New to the site, my first post, Is Stihl the only company with computer controlled timing (M-Tronic)?

 

[Ozhoo]

New to the site, my first post, Is Stihl the only company with computer controlled timing (M-Tronic)?

Welcome aboard. Husqvarna uses Walbro MBU's on some of the 4xx series of homeowner saws. The Walbro link above will give you details on it.
There may be other saw manufactures out there using digital ignition as well.

O

 

[MustangMike]

Welcome aboard. Husqvarna uses Walbro MBU's on some of the 4xx series of homeowner saws. The Walbro link above will give you details on it.
There may be other saw manufactures out there using digital ignition as well.

O

Thanks. Hey, how do you list your saws and change the icon?

 

[pops21]

Put your cursor over your user name in the top right corner of the screen. A drop down will have a link for your signature (to list your saws and such) and avatar picture/video.

 

[MustangMike]

Put your cursor over your user name in the top right corner of the screen. A drop down will have a link for your signature (to list your saws and such) and avatar picture/video.

Hate to bug you, but I got that the "Avatar" is the picture, but I don't see "signature" or any place to enter my saws. Thanks, in advance.

 

[blsnelling]

These saws have timing retard to help with starting. It's not like one coil is going to give any significant performance difference than another. If you want more ignition timing, you do it at the flywheel key.

 

[Saw Dr.]

The newer Stihl coils have similar curves (not the -1300 coil on many popular saws). The pics I have are on pages marked as confidential, so I didn't think I should put them on the internet. The M-Tronic units all use variable timing. It appears that "stutter" type rev limiting has gone the way of the DoDo bird, as the new coils all have a substantial retard curve right about redline RPM.

 

[Naked Arborist]

DM61CCN

That's money if you can get it to fit.

 

[Old2stroke]

What kind of saw is that MB33? Never heard of a saw that has ignition fixed at TDC

 

[president]

Agreed. It's spec'd on the 181 and 42/242. I'm sure there are others as well.

O

for added performance would shaving 20 though off the key ,or sourcing
another coil work?

 

[Old2stroke]

for added performance would shaving 20 though off the key ,or sourcing
another coil work?

Shaving 0.020" all at once is a LOT. Depending on the size of the crank, shaving 0.010" can produce 5 deg change so you should know where the timing is before changing that much. Most stock saws don't get more than 20 deg advance so it would be better to start with less shaving and see if it introduces starter kickback and any noticeable increase in performance.

 

[Huskvarna hotellgäst]

Interesting that the SEM AM7 is so different - it's less advance and not all in until over 7000rpm.

As the OP said, it's an analog ignition, i.e. the point at which the spark is triggered is analogous to the rpm. The longer it takes the magnets to pass all three poles of the coil former, the greater the delay.