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Hey everyone! I've got a Stihl BG 86 blower that I just purchased and runs like crap. Going through all the things it could be, I've settled on the ignition module and flywheel, but my problem is with the CORRECT SPECIFICATION for the gap.

The Stihl software that you folks were kind enough to pass along shows the attached pages in the Workshop Manual, which show the following:
a) from the BG 86 Specs in the Workshop Manual: gap = .15-.30mm
b) from the BG 86 Testing and Setting Data also in the Stihl software = .25mm
c) tool needed from Workshop Manual = 1127 890 6400
d) tool ordered and it's a .35mm setting gauge???

So............., my dilemma is this: What is the correct gap for the Stihl BG 86 blower? One part of the manual says it's .15-.30, another says it's .25mm (which is between .15 and .30), then the tool that's supposed to set this correctly is .35mm.

I set the gap with two .25mm brass feeler gauges on another BG 86 and it runs great. I've even swapped the module over to the older blower to see if the module was at fault, but the older blower an fine. I really think the ignition gap was out of spec on this poor-running blower, though I didn't check it to begin with... :-(

For what it's worth, I've pulled the ignition module and carb off of the poor-running machine and put them on my older BG 86 that runs great, and it still runs fine with the parts off the one that doesn't run well. I'm waiting on gaskets, tank fuel line, and a fuel filter to get the poor-running blower back together to start into the module gap issue, but this specification variance confuses me.

I think that it means that it is not that critical.
I just use a business card.

Fish said:

I think that it means that it is not that critical.
I just use a business card.

Click to expand...

Does make a difference
THe closer the coil is the earlier it will fire
The further away the latter it will fire.
The closer it is the higher the voltage
the further away the weaker the spark

While the spark strength is not normally a problem it can make starting difficult .
I used to fit a lot of the Runtronics DC amplified ignitions to motorcycles .
We used a mounting kit devised by a cleaver lad from the USA to get them tuned properly.
This kit allowed both rotation of the pick up coil and radial movement.
On the big singles running on dope, both wer e needed to get the bike to both bump start and to attain full revs.

I believe there is a typo in the service manual as the 0.20mm setting gauges are PN 0000 890 6401 and 4118 890 6401. The 4118 890 6401 is listed as a .008" which translates to .020 mm.

Now the BG85 did spec up to 0.45mm.

StarTech said:

I believe there is a typo in the service manual as the 0.20mm setting gauges are PN 0000 890 6401 and 4118 890 6401. The 4118 890 6401 is listed as a .008" which translates to .020 mm.

Now the BG85 did spec up to 0.45mm.

Click to expand...

It's confusing for sure. I think I'm going to go with .20 to .25mm and call it a day. I was able to slightly bend some old brass feeler gauges to sort of mimic the curve of the flywheel and avoid the magnetism to get a good feel for the .25mm setting. The blower ran great upon starting, but the specs still just make no sense to me, especially the call for the setting tool at .35mm.
PS: I haven't checked the spec on the BG85 as I've never had one, only BG86 models...

Just think someone wasn't proofing the SM.

Here is the BG85 specs.

Or just use a business card....

Wow. Using magneto voltage to set timing. What will the demons think of next?

Fish said:

Or just use a business card....

Click to expand...

Which what I usually do execpt I use my repair tags.

StarTech said:

Just think someone wasn't proofing the SM.

Here is the BG85 specs.
View attachment 54475

Click to expand...

I've got an 86, not an 85, but if I'm following you correctly, you must be thinking they've got to be pretty close. However, the plug specification for the 85 and 86 are different as well as base idle, in addition to the gap that brought me here...

StarTech said:

Which what I usually do execpt I use my repair tags.

Click to expand...

Yeah, those are good too.