Stihl BG 86 won't start

joe_indi · June 05, 2012, 04:53:13 AM

Quote from: JohnG28 on June 04, 2012, 02:16:28 PM
I'm quite certain the muffler isn't plugged, I've had the screen out and can see inside, nothing at all. As for ignition issues, how would I go about judging if this is the problem? I have seen spark and its not the switch as I tried bypassing it.

The BG86 that sell here have no screens and its a sealed unit.Clogging does occur on these.
The one that I had mentioned in an earlier reply, the one the customer bought from USA had a screen

But, even if the screen is clean, you just cannot be sure 100% that it is not actually clogged, and is the cause of the problem.
The only shortcut method to test this is to remove the muffler and try to start the engine.

There might be a spark at the plug, but, is it sparking at the correct set time?
Even Stihl workshop manuals say that the ignition module cannot be tested to see if it renders the spark at the proper timing.The only way to test is to use another module on the engine.
But removing the flywheel and looking at the taper can tell you if the key is intact.Wrong ignition timing does not mean there is no spark, it comes at the wrong time.

Joe

T Welsh · June 05, 2012, 05:36:58 AM

JohnG28, As Al said in previous post a carb rebuild kit will fix most problems. I am still puzzled as to weather you have a ignition problem or a fuel problem. pouring gas down the spark plug whole will get it to run for a few seconds. and you say it tries to start but doesn't run? Anyway you look at it you will have to eliminate one problem Fuel delivery, Get a rebuild kit and install it (correctly) diaphragms and gaskets in proper order and check fuel lines and vent for proper operation and see what happens. If it still will not start you have an ignition problem and then start at the switch and go toward the engine checking all wires for shorts until you get to the module, as joe_indi said there it no way to check these other than swapping a new one in, also check for a sheared key on the flywheel as Joe said they can shift and the timing will be off and it will give you fits until you realize that it was the cause. Good luck and keep at it!!!!! Tim

lumberjack48 · June 05, 2012, 11:39:47 AM

This might sound a little far out, but i've had it happen. The spark plug i was using had all kinds of spark, grounded out on head. The plug was not firing under compression, i had this issue a couple times with spark plugs.

I think i said this before, i would shut all gas off to saw, dry it out and see if it well run on spray gas. This would eliminate ignition problem's.

JohnG28 · June 05, 2012, 01:46:49 PM

I'll pick up a carb kit and start there, haven't had a chance to grab one yet. The muffler on this has the removable screen and both the screen and inside look clean. I suppose its possible that something could have happened to the key on one of those times I pulled on it like there was no tomorrow. Pulling the flywheel doesn't sound like much fun, a pain as I understand. If I end up getting there I'll let you know. I do wonder if this is ignition related as it died at wot without any hint of an issue and not run since. Strange though that it was flooding out and now isn't.

lumberjack48 · June 05, 2012, 03:46:58 PM

Take the rewind off, lay it on it side and turn flywheel by hand, when under compression, look and see if mag and coil are lining up. If the key is sheared off the flywheel should have some movement in it. If it is sheared you wouldn't need a puller to get it off.

Flywheel is pretty simple one nut and a tap and its off.

JohnG28 · June 05, 2012, 09:31:08 PM

There wasn't much play last I had it apart. It seemed to be right on, reached peak compression right as the magnets passed the coil and there was a definite push through the coil by them.

T Welsh · June 06, 2012, 06:57:50 PM

JohnG28, Another little trick if you have the side case off is to stick a 12mm socket or what ever size flywheel nut is on an air gun and ground the spark plug on the head and spin the engine dry and watch for good running spark. Tim

thl · June 12, 2012, 04:44:41 PM

I've got a BG 85 that ran fine up until last fall when it slowed and finally quit. Just got around to checking fuel. Thats's fine however the after using the trick mentioned about spinning the flywheel with an air gun and grounding the plug I find that I do not have spark. Connections seem fine. I'm guessing coil? Comments?

Thanks,

Terry

T Welsh · June 12, 2012, 07:09:46 PM

thl, Your suspicions are probably right! Dead coil, But first there are a few things to check before going to get a new coil. Double check all electrical connections to make sure it is not grounding itself out, check underneath the flywheel for shorts in the wires,check to see if woodruff key is not sheared or twisted allowing timing to be off. If all good then its time to visit Mr. Stihl. Tim

JohnG28 · July 12, 2012, 07:21:41 PM

OK, so I'm a little late on getting to this but better late than never. So I got the carb kit finally and installed it. Result was more of the same. >:( Dry plug and not a sputter. Soooo, I'm up for any further suggestions. Shop looked it over when I picked up the kit and were pretty puzzled too. Comp is good, p/c look like new, has spark which they verified also. Plug was dry after this last try. Still haven't pulled the flywheel. Is there a trick to.getting it off once the nut is off? Don't really want to break anything. Thanks.

JohnG28 · July 21, 2012, 06:31:24 PM

So I messed around with this some more last night. Fuel through the plug hole got more sputters, wanted to start but nothing again. Dried plug and cylinder, tried again, wet plug then nothing. Dried and tried again, now dry plug and nothing. I'm really confused and close to taking it to the dealer, really don't want to. I did find the gap between coil and flywheel was close, reset with a business card and tried again. Nothing!!! Any final suggestions anyone?

Paul_H · July 21, 2012, 06:57:21 PM

Quote from: joe_indi on June 04, 2012, 01:59:34 PM
If the resultant noise wont be a bother, try starting the blower with the muffler removed.
Does it start without the muffler?
Joe

I would try running without the muffler as Joe suggested,it only takes a minute to remove it.No blow,no suck and we've seen the same problem here in the shop where the engine would run without the muffler but not with it.

westyswoods · July 21, 2012, 07:15:11 PM

Don't know if this applies in you situation but check to see if there is a kill switch or wire shorted out somewhere. I had this happen several years ago with a Stihl saw, the kill switch was not clearing properly. Just a thought may not apply

Westy

JohnG28 · July 21, 2012, 11:46:48 PM

I'll give it a try. I'm up for anything before the dealer. Thanks

T Welsh · July 22, 2012, 06:23:06 AM

JohnG28, If your getting it to sputter by pouring mix in the spark plug hole, your on to something! It tells me that you are NOT getting fuel to the engine.It is firing up until it runs out of fuel. You need to start at the beginning and look at all systems of the fuel delivery system and make sure everything is right. Start with the filter in the tank fish it out and remove it and make sure it flows gas,blow the fuel line out with air. check impluse line for cracks,remove carb and disassemble and verify you have all components in the right order, reassemble and try again! I know this gets frustrating, but look at the expirence you are getting and the money you are saving by doing this yourself. Trust me you will find the problem and weather you or the shop fixes this, you will be the smarter person in the end. Good Luck! Tim

joe_indi · July 22, 2012, 06:31:58 AM

Quote from: Paul_H on July 21, 2012, 06:57:21 PM
I would try running without the muffler as Joe suggested,it only takes a minute to remove it.No blow,no suck and we've seen the same problem here in the shop where the engine would run without the muffler but not with it.

Very true. I have had blowers and hedge trimmers come in with blocked mufflers, not from carbon or oil, bur roaches, bugs geckos and small frogs!
Once the muffler causes any kind of resistance the air flow is stopped and no fresh fuel or air can be sucked into the crankcase.

Quote from: westyswoods on July 21, 2012, 07:15:11 PM
Don't know if this applies in you situation but check to see if there is a kill switch or wire shorted out somewhere. I had this happen several years ago with a Stihl saw, the kill switch was not clearing properly. Just a thought may not apply

Westy

Precisely what I suggested:

Quote from: joe_indi on June 01, 2012, 04:23:46 PM
Today I had a BG86 that came in for repair with a sort of similar problem.
When the starter was pulled, it would just kind of burp and, that's it, it just wouldn't start.
The problem was the stop switch wires were kind of mashed together in a groove that seats the starter cover.
So, the ignition keeps cutting off.
On a spark plug you get a spark, but maybe only erratically.
To confirm that this was the problem, I disconnected the stop wires from the ignition module and tried starting the blower.
It fired on the first try.
Strangely, this was a fairly new machine which the customer had brought with him from USA when he came back home for his annual holiday.
Maybe, instead of looking only into the carb, you should also look for other causes like this one.
You never know.
Maybe a flywheel that's moved out of its position due to a sheared key.
Maybe something else.

Joe

martyinmi · July 22, 2012, 07:12:15 AM

John,
I ran into a situation nearly identical to yours that had me pulling out what's left of my hair a few weeks ago. The 1 year old Stihl leaf blower was sitting on my bench at work with a note that said: "please fix-won't start-full of gas-has spark". I tried everything I could think of for about 2 hours(as well as new line,filter), and was down on myself and ready to throw the dumb thing across the shop. An older retiree(he is 69) we have working for us came in the shop and and asked what was going on, as well as what all I'd tried so far. He suggested COMPLETELY draining the fuel system, mix a new batch of gas, and have that be my starting point. I did as he suggested, knowing full I was wasting my time. After the new fuel and about 8-10 pulls, it fired and ran like new after about 30 seconds. It turns out one of the part time high school kids accidentally used on-road diesel fuel when he mixed the last batch of gas. There was just enough gas left in the container when he made a new batch to make it both look and smell like it should.
I was embarrassed by this old fart, and he won't let me forget it :-[ So if I were you, before letting the dealer mess with it, I'd try new fuel

Paul_H · July 22, 2012, 12:00:10 PM

We get trimmers and saws with diesel fuel too.I think the marked fuel fools some people into thinking it's mixed.There is no mistaking the taste of diesel smoke.
Most times we can dump the fuel and replace with proper mixed fuel and keep the engine running with a shot of gas in the throat of the carb long enough that the system is purged.

JohnG28 · July 24, 2012, 03:23:26 PM

Update on the latest today - pulled the muffler and mixed a new batch of fuel. Still nothing with new fuel and muffler off. It seems like there's no fuel again. Spark was still strong. I did regap the coil, as there was almost no clearance between it and the flywheel. Verified spark after, still nothing. Still at a loss......

Paul_H · July 24, 2012, 05:15:02 PM

What does the piston look like in through the ex port? Any scoring on the piston,is the port clean and unblocked?

JohnG28 · July 24, 2012, 05:34:06 PM

The piston and cylinder look like new. No scoring at all, no carbon, no blockage.

joe_indi · July 24, 2012, 11:25:57 PM

You got a good cylinder and piston so compression is OK
You have tried 'spoon feeding' fuel into the cylinder
There is a spark at the plug.
These are the three basic requirements of any IC engine and you have them.
But the engine does not pop.
One of the three is not in line.
I would check the ignition coil and flywheel.
Unless you get that spark at the right time(ing), that engine will not pop.
That ignition coil has a speed limiter built into it. If that malfunctions you will not get a spark for starting the engine.
If you can lay your hands on a tachometer, with the spark plug removed, check the minimum reading when you pull on the starter, just fast enough to get a reading (100-120). Pull faster and check if the reading increases substantially. If it does not, try another coil.
But before you do all that, move the flywheel till the piston is just before TDC. The magnets should be nearly aligned with the coil. If the magnets have moved forward from the coil, remove the flywheel and check the position of the key.

Joe

joe_indi · August 23, 2012, 08:21:17 AM

Terry,
Thank you for starting this thread.I could use it as a checklist today.
I had a fairly new BG86 this morning which was dead. That is till I found the cause.It was a faulty kill switch. This machine has a Normally Off' type switch. When you press the stop switch the switch turns on and the engine stops.Since it is spring loaded it returns to the Off position. In this case the switch was a bit stiff from dust so it was more of a Off-On situation.
Once I cleaned out the switch it worked again and the blower started up on the first attempt.
Joe

JohnG28 · August 23, 2012, 06:10:32 PM

Thanks for that info Joe. Truthfully, I have put that blower in a corner for a while because I was so frustrated and sick of it. Plan on some work this weekend including reassembling most of a MS200t project. While I'm at it I'll pull the kill switch out and look it over to see if it's sticking. Thanks!

JohnG28 · September 19, 2012, 12:26:20 PM

Well yesterday I took some time to get back into this blower. First try to just start it got nothing, and the plug was dry, so no fuel. It will all but crank over with a squirt of fuel into the cylinder, but just won't quite kick over. At the same time it's also spinning the nut and washer off the impeller side now, just as it's almost starting. I can pull on it all day and that nut won't loosen, but soon as it wants to start it spins off. Now I'm thinking this could be that the timing is off slightly, causing it to fire just a little too soon? And back to no fuel to boot. I did try bypassing the switch completely, and that didn't change anything, so I think the switch is not an issue.