Help with Stihl FS 45 trimmer

[Wonkydonkey]

So if your flywheel is not at the coil yet, and it is at tdc,

It is trying to fire atdc. If you check the keyway is in the correct position on the crank and check the pic on page 5, see below. (Remember the pic is at bdc) you should be able to work out what you have ie new or old model and what coil..etc., and if you were to check the carb you have that should also help. See a few pages on in the bulletin as to which carb is on new or older models.

I don’t know if you have had this from new and stihl have Foobared in the assembly line, or someone has changed covers with serial no's on.

But failing all this, I think if you were to rotate the flywheel just past the mags ( rotating counter clockwise) while at tdc it should work...

 

[GBertolet]

My understanding is, there is a difference in the electronics, between the coils, determining the timing of the spark. As mentioned previously by the forum experts, the flywheel crankshaft and flywheel are in a different relationship position, between the old and new model FS45's, which facilitated a timing change. Keep looking on Ebay, or some vendors that may have N.O.E. stock. Maybe even check with a power equiptment shop, that might have old trimmer to part out.

 

[Boots]

So if your flywheel is not at the coil yet, and it is at tdc,

It is trying to fire atdc. If you check the keyway is in the correct position on the crank and check the pic on page 5, see below. (Remember the pic is at bdc) you should be able to work out what you have ie new or old model and what coil..etc., and if you were to check the carb you have that should also help. See a few pages on in the bulletin as to which carb is on new or older models.

I don’t know if you have had this from new and stihl have Foobared in the assembly line, or someone has changed covers with serial no's on.

But failing all this, I think if you were to rotate the flywheel just past the mags ( rotating counter clockwise) while at tdc it should work...

Yes I've had this since new, it was in the box from when I bought it in 07, I just took it out and used it a few times this past summer, then the coil blew. Everything on the right side of that bulletin is what my machine has so its the "updated version" but STIHL USA doesn't have the correct coil for it anymore. They say the 1308 works but they are dead wrong. It's really not worth my time and effort to grind a new keyway slot for a 250$ weed whacker. I'm just going to strip the good parts and toss it if I can't find a 1303 coil by spring time. Thank you for the help.

 

[Boots]

My understanding is, there is a difference in the electronics, between the coils, determining the timing of the spark. As mentioned previously by the forum experts, the flywheel crankshaft and flywheel are in a different relationship position, between the old and new model FS45's, which facilitated a timing change. Keep looking on Ebay, or some vendors that may have N.O.E. stock. Maybe even check with a power equiptment shop, that might have old trimmer to part out.

Yeah, I'll give some repair shops a call and see if I can rummage through their junk piles.

 

[Arvorsteve]

Hi guys and thanks for letting me join your forum. I think I have the same issue here with timing having tried a Chinese 1308 coil clone and would appreciate your help.
History
Bought this FS55 2007 model S/N 67573628 strimmer at a boot fair here in the UK as not working. Where I am with this now I have to assume that the outer case may not be the same age as the parts that are inside and that this maybe a 49, 59 Chevrolet, you all know the song. Therefore it might not be a 2007 model at all!
Build Spec
From the tech data posted by Fish and observation of the key-way position it's got the later 4140-030-0401 crank, so that's OK for a 2007 model, although that number does not appear on the crank itself. It's also got a flywheel with no central cast in aluminium boss and has the number 4140-400-1201A (or 12C1A hard to tell) I think it's an earlier version, hence my suspicion about it being a hybrid. Can anyone confirm to me if the 1201A or 12C1A is indeed an earlier flywheel please as I don't see it in the parts list posted earlier?
Can anyone tell me the difference between the flywheels as the later one with the raised central boss also seems to have the key way inline with the magnets. What's the difference in them that matters with the timing or are they all interchangeable with the coils?
The fitted coil is the STIHL Walbro 4140-1303A coil and it is not producing a spark. Gap is correct, flywheel Woodruff key is fine, it hasn't slipped.
Tests to date
Removed engine from casing, good compression, no scoring of bore.
Removed kill switch
Tested coil as being U/S and purchased a so called Chinese replacement coil which as everyone has confirmed so far , is now the 1308 coil. I don't see that STIHL are making two coils for this machine, although it appears they should be making a 1303A rip off?
Fitted the Chinese coil, good spark, but back firing through carb, you know the problem.
At this stage I happened on this thread but what I can't see anywhere in it is a technical explanation to what's going on here between these Chinese coils and the STIHL OEM parts. Some of you seem to be saying that fitting a STIHL coil cured their issues, but as we have read above from Boots, the STIHL coil didn't work for him.
Further Tests
From visual inspection the 1303A coil (including the Chinese clone 1308 which looks identical) aligns with the magnets on the flywheel at TDC
I remounted the discarded STIHL 1303A coil and measured the resistances with a DMM and I get 43 ohms on the low voltage side to earth and 2.7Kohms on the high voltage lead to earth, so not open circuit but maybe shorted turns. Anyone know what resistances I should be getting?
I also put the engine in my vice, set it up with a battery drill, plug out, oil down bore and scoped the output of the coil as I rotated the crank. I am getting around 1.5V peak to peak on the low voltage and 600V peak to peak on the high voltage side, so insufficient to fire the spark plug, but interestingly getting some output from the coil.
From this I determine three possibilities.
1) The coil is 'soft', maybe shorted turn on the LV side as I would expect more than 1.5V. Anyone comment on that?
2) The magnets in the flywheel are no good, but I discounted this as the Chinese coil gives a good spark.
3) The air gap between coil and magnets is too big. This has also been discounted because it seems to make no difference on coil output varying the gap between .0001" and .0020"
I baked the coil in the wife's oven (after she went out!) but that made no difference either.
Summary of my questions
Are there any key-way to magnet position variances in the different flywheels as I can't see any?
Do you reckon that a 4140-400-1201A (or 12C1A) flywheel is compatible with a 4140-030-0401 crank and a 1303A coil?
Do you reckon that a 4140-400-1201A (or 12C1A) flywheel is compatible with a 4140-030-0401 crank and a proper STIHL 1308A coil?
Is a STIHL 1308 coil supposed to cater for both the earlier and the later style of cranks and for any flywheel combination, given that they no longer make a 1303A?
If STIHL only make the one 1308 coil how do they cater for an approximate timing variance between the two cranks of 40 degrees with just the one coil if the flywheels are the same?
What's the difference between a STIHL and Chinese coil and why can't the clever Chinese make a coil that works when they seem to be able to make just about everything else in the world
Next Steps
I cannot get hold of a 1303A coil here and reluctant to buy one second hand even if I could anyway as there's no come back.
At this stage I am also now thinking of re-ordering a Chines 1308 coil, filing out the key-way and just playing with the timing until it fires. Drill and tap a hole in the flywheel and peg it to the crankshaft in the right place.
Or will the proper STIHL 1308 coil work do you reckon?
Thanks guys and sorry for all the questions in my first post!
ArvorSteve

 

[Wonkydonkey]

Hi,, Steve ? I’ve just seen your post.
It was a long read, I will have a go at replying tonight

 

[GBertolet]

I am the original OP of this thread. On the FS45 which this post was about, there was a production change around 2002, on the flywheel, and crank, on the timing. I don't know about the FS55, but it might be the same. The 1303A was the original coil, which was bad, and I was told the 1308 was a direct replacement. I bought one, had spark, but the engine would not run. I later learned of the aforementioned timing change, so the electronics inside the coil were different, in deference to that. The 1303A was the only coil to use. I found a used one on ebay from a parted out trimmer. I took the chance, and bought it. It was relatively inexpensive. You may have to do that also.

 

[Wonkydonkey]

https://www.ebay.co.uk/itm/Stihl-FS...311562?hash=item4b805093ca:g:AhEAAOSwB95fR9vh.


Ok I’ve got a short amount of time before I have to get ready and go out, but before that I’ve got to eat.

I have a quick look on eBay, as your in the uk Steve, 2nd hand ones come up often. You can normally see the number on the coil. And you just have to ask the seller. What’s the number on the coil etc.

I would first look at your keyway in your crank and the position it is to the pic’s in the bulletin, once you know your keyway, then you can see which coil should work. From what I understand, it’s only the keyway that is different the fly wheel is the same, if you look closely in the taper of the flywheel, you should see a mark where the cast key has/was, probably someone knocked it off. By accident or on purpose I don’t know.

if your not in a rush I can have a closer look at mine. Later this week and take some pics for you, but it will
Btw. All the coils were the same for the models fs and the hedge trimmer ie before the 1308
sometime it’s unfortunate the coils do go bad and when they do you can’t normally fix them.

The Chinese copied the stihl coil but when I brought mine it was listed as a universal but it only worked on one of the strimmer s I had. And as you know it’s apita if it’s wrong.


so take a pic or a few and post them here, we should be able to help
Work out which pic (left or right) your crank matches best at bottom dead centre. It from page 5 of the bulletin on the first page of this thread.
I will have a read when I get back from the Homebrew meet up.

 

[Arvorsteve]

I am the original OP of this thread. On the FS45 which this post was about, there was a production change around 2002, on the flywheel, and crank, on the timing. I don't know about the FS55, but it might be the same. The 1303A was the original coil, which was bad, and I was told the 1308 was a direct replacement. I bought one, had spark, but the engine would not run. I later learned of the aforementioned timing change, so the electronics inside the coil were different, in deference to that. The 1303A was the only coil to use. I found a used one on ebay from a parted out trimmer. I took the chance, and bought it. It was relatively inexpensive. You may have to do that also.

OK thanks.
If I understand you correct a new STIHL 1308 probably won't work then. This would make sense with such a large timing difference. Just a bit surprised our Chinese friends aren't making a 1303A ripoff. I have looked at several advertisements on Ebay and most of them say their coils won't work for a 1303A, although I did have one seller swear blind it was a suitable replacement when it wasn't.

 

[Arvorsteve]

https://www.ebay.co.uk/itm/Stihl-FS...311562?hash=item4b805093ca:g:AhEAAOSwB95fR9vh.


Ok I’ve got a short amount of time before I have to get ready and go out, but before that I’ve got to eat.

I have a quick look on eBay, as your in the uk Steve, 2nd hand ones come up often. You can normally see the number on the coil. And you just have to ask the seller. What’s the number on the coil etc.

I would first look at your keyway in your crank and the position it is to the pic’s in the bulletin, once you know your keyway, then you can see which coil should work. From what I understand, it’s only the keyway that is different the fly wheel is the same, if you look closely in the taper of the flywheel, you should see a mark where the cast key has/was, probably someone knocked it off. By accident or on purpose I don’t know.

if your not in a rush I can have a closer look at mine. Later this week and take some pics for you, but it will
Btw. All the coils were the same for the models fs and the hedge trimmer ie before the 1308
sometime it’s unfortunate the coils do go bad and when they do you can’t normally fix them.

The Chinese copied the stihl coil but when I brought mine it was listed as a universal but it only worked on one of the strimmer s I had. And as you know it’s apita if it’s wrong.


so take a pic or a few and post them here, we should be able to help
Work out which pic (left or right) your crank matches best at bottom dead centre. It from page 5 of the bulletin on the first page of this thread.
I will have a read when I get back from the Homebrew meet up.
View attachment 256951

Hi and thanks
I have the later crank as I identified that early on from page 5 of the tech sheet posted by Fish.
My interest now lies with whether or not a genuine STIHL 1308 ( not rip off Chinese) coil will work. I can't see how it can given the timing differences but pretty sure I read in one of those earlier posts that someone had bought a STIHL 1308 to replace a 1303A coil and it did work.
If it is the case that a STIHL 1308 is not a suitable replacement then that would imply that STIHL are not supporting the older models. I couldn't find anything that would suggest they took that step.

 

[Arvorsteve]

Hi and thanks
I have the later crank as I identified that early on from page 5 of the tech sheet posted by Fish.
My interest now lies with whether or not a genuine STIHL 1308 ( not rip off Chinese) coil will work. I can't see how it can given the timing differences but pretty sure I read in one of those earlier posts that someone had bought a STIHL 1308 to replace a 1303A coil and it did work.
If it is the case that a STIHL 1308 is not a suitable replacement then that would imply that STIHL are not supporting the older models. I couldn't find anything that would suggest they took that step.
I just had another thought. If I have the later crank and there's no discernible difference in the flywheels a genuine STIHL 1308 coil should work shouldn't it?
Please trust me when I say I have the suposed later crank as per the right hand photograph of page 5 of the tech data. Several engineering friends have double checked my opinion. Could the two photos be marked up wrong.?The more time I spend on this the more confused I get.!

 

[Hickory]

Take a quick look and rotate the flywheel to tdc, then see where the magnets are in relation to the coil.
I did have one new block that the keyway and crank position were way off.

I may have a similar problem with a FS45 (OP hope it's okay if I toss in a question, thx). Original owner, I've replaced the carb and fuel lines otherwise it's been OK. Recently I'm experiencing a slightly harder pull start. It's fine when I pull the plug out. But still difficult after the muffler/spark arrester is removed. It may just be that I'm getting old because after it's been running for a while the pull starts are not all that bad.

So a couple questions:

How should the magnets be positioned at TDC?
Do I need to pull the flywheel to see the key?
Since it's running fine, no backfires etc. does it mean that the key is OK?
Any other positioning cues that I should check? (I downloaded the bulletin and have yet to figure out which I version that I have)
Should I just leave it alone since it runs fine, or am I headed towards a bigger problem?

thanks in advance.