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Stihl BR340 Backpack Blower Spits Back out the Carburetor


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  #21  
Old 06-02-2018, 11:25:47 PM
GADavis GADavis is offline
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

Quote:
Originally Posted by I like oldstuff View Post
Is it piston port or reed valve. If reeds, look there.
Some Sthil blowers are 4 cycle engines and have valves that need adjustment occasionally. check to see if this might be one.
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  #22  
Old 06-03-2018, 10:29:18 AM
s100 s100 is offline
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

I stated in post one and reiterated later that this is a third port two cycle engine.
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  #23  
Old 06-12-2018, 07:52:23 AM
edward moller edward moller is offline
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

I have seen a lot of stihl equipment with blowback at wide open throttle. one very unusual problem i noticed, had a blower that would lose power slowly. put it one a bench outside, wired the throttle wide open , let it run by it self for about 20 minites. when it started to slow down went to look at the carb & noticed a small piece of ice had formed in the throte of the carb. right humidity & temp, carb icing.
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  #24  
Old 06-12-2018, 08:14:41 AM
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

Feed it new piston rings.
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  #25  
Old 06-13-2018, 06:39:39 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

I too would re-ring and do a glaze break on the cylinder. I also would have a careful look at the piston itself for ring fit in the grooves and end gap. Look also for discoloration and scoring on the piston itself. Even though you are using a mix heavy on the oil, Sthil uses a lubricant that is specifically made for their equipment. perhaps your wallyworld oil is not up to the task. you have certainly got your moneys worth out of the blower, perhaps it's just wear and tear catching up over time. try lifting and depressing the flywheel to check for bearing wear. Can't hurt! if you pull the flywheel and can get to the PTO side of the crank, try putting some soapy water on the crank, where it leaves the seals and see if there is any leakage. seals wear and harden with age. could be time for a new set.
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  #26  
Old 06-13-2018, 08:48:35 PM
s100 s100 is offline
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

As of this writing the Stihl is back together and seems to be running okay again. I did not completely disassemble the engine, I just removed the externals. From what I could see through the rather large intake and exhaust ports both the piston and the cylinder look fine, especially considering the machine's age and amount of use. It's true I have not had occasion to run a couple tanks of gas back to back through the engine but five or ten minute runs on a very hot day presented no challenge. I'm not suggesting that this will continue but so far so good.

As I stated a few posts back, the engine acted up once again after reassembly but that was resolved by adding gas to the tank. It wasn't out, and in the past the machine would suck the tank dry then stop dead. Who knows, maybe there is some issue with the fuel pickup. I don't think it is a cap vent issue because if it were the engine would start and run fine when the cap was loosened or removed and that was not the case when the problem was presenting.

Given the machine's overall condition it is not worth putting much if any money into it. If it starts acting up again I will reconsider the idea of looking for a (very) cheap set of rings for it but that's the extent of what I would put into the machine.

For now, given that we live in a very imperfect world, and have a very finite amount of time to devote to any one thing, I consider the problem solved. And it's not like the problems quit coming. I went out to trim a long hedge the other day and my little Echo hedge trimmer is on strike. Bought it new sometime around 1983 and gave it very little use. Still looks good as new. But the electronic ignition has been flaky for some time and finally gave up the ghost. I checked a few years ago and I think parts are NLA for that model so I may have yet one more tiny bit of yard art. Oh for the good old days of points and condensers....
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  #27  
Old 06-14-2018, 06:55:19 AM
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

Quote:
Originally Posted by Andrew Mackey View Post
I too would re-ring and do a glaze break on the cylinder.
Chrome bore. Don't even think about touching it with any type of abrasive.
The ring or rings are shot and allow combustion to blow past them and ignite fuel in the crankcase. That's the carb poof that is happening.
This event also burns off oil on the piston and cylinder which will seize the engine. Then the whole thing goes into the trash can.

I was just given a virtually new Stihl blower that was shot after only ~ 20 minutes of operation.
OLD GAS. Alky gas will kill a two stroke in short order. Dealers now have test kits to determine fuel condition. If it doesn't pass, no warranty.
This one gummed up the ring in it's groove and had no compression. I took it apart and put the piston in the ultrasonic and after an hour the ring let go of it's death grip. It now runs like the new machine it is. Of course after I dremmeled off the limiter caps on the carb adjustment screws and gave it the fuel it needs to run.
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  #28  
Old 06-14-2018, 08:18:55 PM
s100 s100 is offline
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Default Re: Stihl BR340 Backpack Blower Spits Back out the Carburetor

"Just go buy one of those battery trimmers."

I hate everything about batteries! I hate them almost as much as they hate me. I was thinkin' on this the other day when I had to do some work away from an electric source. I have a battery drill I bought at Sears (anyone remember them? Poor Sears!) and every time I pick it up it is dead - and not rechargeable dead, but stone cold buy a new battery dead. So I'm out 25 bucks to drill a couple holes or drive a half dozen Teknopoint screws. The only reason I bought it is because it came with a powerful flashlight and that seemed like a good thing to have, but it's always dead too. So now the drill, the flashlight, the charger, the carrying bag and a half dozen dead 19.2 volt batteries have taken up a prominent new home on my shelf of remnants of "good ideas I wish I never had". Now I get those FREE little flashlights from Harbor Fright and they are great. So no battery tools! Not ever. Bad enough I have to dink around with adulterated gas and transistorized ignition.

"The ring or rings are shot and allow combustion to blow past them and ignite fuel in the crankcase. That's the carb poof that is happening."

There is NO carb poof or combustion inside the crankcase. None. Zero. Purge that notion from the memory banks. If that were the case it would have melted all sorts of plastic goodies in the carburetor and the air cleaner box. In fact given that the foam air cleaner element becomes the repository for some of that gas that is spit back, if a backfire of any sort occurred that thing would go up like an incendiary grenade, and since it is a backpack probably take me with it. Compression is not arm wrenching but perfectly adequate for a machine of that displacement and age. I was able to see the rings when the piston was adjacent to the exhaust ports. Using a little probe I was able to wiggle the rings. They are not gummed or carboned up.
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