Tuned 395xp - ignition timing

[htb]

Actually watching Mont Don at the moment, but can follow you though.

[spudulike]

Is that Monty Don, the Gardeners World fella? Not sure he would know anything about ignition timing

[htb]

He doesn't but an interesting programme none the less.

[bmp01]

Thanks for the detailed reply Spud.

I don't think there is much chance of a comparison with a standard 395...I've only ever seen one, that 'one' came home with me ? ?

It's a thought though - comparing to std. I think I only need a standard flywheel - if the comparison is done statically I can get my saw locked up against an accurate piston stop swap in a standard flywheel, marking position, swap to my flywheel on and see how it lines up. Don't even need to torque the standard flywheel up.

But let's say I'm happy with what I know about the timing as it is,  let's say it's 19 degs BTDC. If I do a similar thing,  accurate piston stop and mark the relative position of flywheel to housing before disturbing the taper. Then even after I've disturbed tbe flywheel I can get the piston stopped in the same place and I can rotate the flywheel to align the marks.

Even better, I can also retime it (say) 5 degrees by moving it 5 mm (such a happy conversion).

 

Soooo, back to the timing question......

 

 

[spudulike]

I think you are expecting the unlikely if you think someone will know the ignition timing of the 395 so you can dial yours in exactly with a strobe and think it would test even the guys at Husqvarna.

Much depends on the accuracy of your gauge and am guessing you are using a timing wheel to graduate this and a strobe to measure against it.  

My Red Eye ended up at around 30 degrees from a Stihl spec of 27.5 - 32 degrees so think your 19 degrees will ebb away power as I reckon it is a bit conservative.

Probably better that someone with a 395 can lock the piston and photograph the flywheel or wait until perhaps I get another one in. Shame as I have just done one over the Christmas break. I have done a few MS150s like this that have sheared their key and got the timing bang on and is a reliable method.

19 degrees won't bugger the machine up, if you take it too far, the machine will rumble in a most disconcerting way - my saw did and made a noise that spoke to me - it said, "you open the throttle, I will grenade"

[bmp01]

20 minutes ago, spudulike said:

if you take it too far, the machine will rumble in a most disconcerting way - my saw did and made a noise that spoke to me - it said, "you open the throttle, I will grenade"

Love it ! Absolute classic ! ??

 

Yeah, wasnt really expecting exact degrees,  it was more of a summary statement (coming back to timing question) having resolved in my mind the way forward.  Up till you mentioned the piston stop thing I hadn't really seen how to change the timing by an accurate amount (or keep it the same). In my mind I'd lost all reference once the flywheel was off, so thanks for that. 

I think I'm shooting for around 24-26. As you say 19 is too low, I was a little disappointed when I measured that's what it was. 30 has me twitching a bit and well y'know, I'd like to think I've gained turbulence and flame speed with the combustion chamber I have (wide squish band, 0.50mm clearance).

 

But I will, without a doubt, be listening for those 'don't fxxk with me' noises. Too much time into this saw to nuke it.

[spudulike]

With a saw of this value, I know what I would do and that is using the stop method. With the MS150s I use a very specific method for stopping the piston that has worked on a few that have sheared their keys as yours has and it gives a very precise result rather than guessing as we are discussing whether the advance is 23 or 30 degrees. The coil may also be smart with different rpm/advance ramps so difficult to gauge.

I cant tell when the next 395XP will roll in, they are usually fairly common but having said that.......

What we need is a 395XP owner with a little engineering experience and a camera!

[bmp01]

Thanks for the that Spud, next time you have one in then. ....

 

Checked the coil and rechecked it's behaviour this morning.

First thing,  it's blue, so that's a limited coil. Part no on the coil 810 204 16 also has SEM and AM44. The Americans think it should be a black unlimited coil. L&S Engineering list part number as 503 63 98-01

 

Second thing, (with this coil) from idle (2800rpm) upwards it's fixed timing. Retarded at cranking speeds (think battery drill cranking, spark plug out, ~1000rpm) by 30 degs or there abouts. And yes the tach and timing light go beserk as it starts misfiring. ...

 

Edit - I've had no luck identifying the  coil 810 204 16 online, no idea what its from. 

Edited January 11, 2020 by bmp01
As per edit note.

[spudulike]

I don't think I have ever seen a blue limited coil on a 395XP, they are usually black and unlimited and some of the machines I have seen in have been under a year old so that's a bit strange.

It should be part number 503 63 98 01 and your part number makes no sense.

The SEM bit makes more sense and shows an ignition ramp up of 8 degrees from idle on this webpage -  

Small engine ignition systems Properties - SEM AB - MAFIADOC.COM

MAFIADOC.COM

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Suitable for engines that require a flat ignition curve. Ignition voltage. Using effective electronics, a maximum ignit...

 

[htb]

Can check which coil is on mine the morn, if of any use.