Stihl BG86C Leaf Blower

[Loki]

Observations:
1.Engine starts, although can be stubborn at times, but other times easy to start. Runs for a short while and sometimes well.
2. Runs erratic in the sense it will run fine and accelerate well at times but will always bog down after a short time, decrease rpm and die.
3. Under full throttle the engine decreases RPM for a short while, then no throttle response and then dies.
4. Hard to start from that point, and more than likely will not start even with choke.

What Ive done:
1. Fitted a known good carb, tuned it and symptoms persist.
2. The muffler has the gauze removed and breathes fine.
3. Air filter thouroughly cleaned.
4. Fuel tank cleaned out and useing fresh 2 stroke fuel, petrol or (gas) depending on where you from.
5. Fuel lines checked and appear supple and no cracks.
6. Breather replaced with a known working one.
7. Endoscope camera into the bore, piston and cylinder walls look near new.
8. Rings sit loose and show no binding to piston.
9. Changed sparkplug. i removed the sparkplug after pulling rope a few times and I saw the plug had fuelled up.
10. Checked spark (plug short to body) and seems to spark although looks a bit weak, but electronic ign coil spark is are sometimes hard to see. The old points system threw out a big blue spark.

Whats left:
1. Checked the fuel filter, it was clean but unsure whether it has diminished porosity and possibly starving the fuel flow? There is quite a bit of resistance when blowing through some fuel hose with filter attached.
2.Flywheel key partially sheared?
3.Coil breaking down although Im unsure whether that would make the engine decrease in RPM.
4.Crank seals? Although leaks there usually produce momentary leaning out and increased rpm? Maybe not?

For the moment Im stumped. Ive worked among these BG series blowers for a number of years and found carb probs seem to top the table. Appreciate any help LOKI.

[KE4AVB]

I now the following is list several different things that can cause problems and it is just process of elimination.

Have checked the fuel tank vent? A none working vent can cause fuel starvation and shows up rather quickly on full tanks.

What color are flywheel magnets? If they have turn blue then they are probably bad and would cause erratic ignition problems.

Have you done a pressure/vac test of the crankcase for leaks. I had a couple Stihl units with bad cylinder to crankcase gaskets last year.They only show up after warming up.

Also do a compression test on cold and hot engine then compare the results. A wet plug with working ignition is usually a sign of compression problems. If cylinder is clean may be worn ring.

[okie]

Hello Loki

I don't have any ideas beyond those presented by you and Ke4AVB. I would like for you to please keep us up dated. I am interested in your problem.

Thanks

Okie

[Loki]

Thank you for your input All. I will keep on with it and try and diagnose it and report back.

I work in a large garden maintenance company and among the inventory is about 10 x BG86C Blowers I service and repair as needed. Ive never seen this type of problem before, I have a spare working coil which Ill try but its not the typical coil symptom I've experienced.

Crank seal leaks tend to make the engine lean out and sometimes scream RPMs but its not doing that. If the crank cover seal is faulty id hope to find a bit of tell tale leaky fuel residue around the mating surfaces but Im only speculating.

I have a crankcase / carby test pump, have to make flanges etc to seal over the exhaust and inlet.

QUESTION: Been years since Ive had to use this, Do I seal the inlet and exhaust ports and pressurise through the spark plug hole? Need to make a plug hole adaptor. thanks Loki.

[KE4AVB]

QUESTION: Been years since Ive had to use this, Do I seal the inlet and exhaust ports and pressurise through the spark plug hole? Need to make a plug hole adaptor. thanks Loki.

Provide there is not a separate pulse line which I don't see then yes. Stihl uses a carburetor side adapter but that just the way they do it.

[Loki]

Gday All, I never resolved this problem blower. I changed out every item/part on the blower with a known working one, I resealed the crankcase halves and new crank seals. I did not replace the piston, rings or cylinder as they present as near new. Thanks Mr and Mrs Stihl.