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Discussion Starter #1
So my father's BR320 Stihl blower is about 11 years old, and recently it has taken to not starting when the engine is warm. I thought he was crazy, but now all the sudden my BR340, that is about 7 years old, has taken to doing the same thing. Anybody have any ideas what would cause this? I'm guessing ethanol has caused something to deteriorate, but who knows.
 

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GANG GREEN GIZMOW KILLER!
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Check your tank vent.



Sometimes if the vent is blocked the heat will make the gas expand and flood the engine.
 

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Discussion Starter #3
I didn't check the vent, before I pulled the cord a second time I did remove the cap and put it back on to be sure there wasn't back pressure. Yesterday when this happened I pulled once, vented the cap, pulled it a few more times at the curb, then brought it up to the garage and topped it off. The gas is almost new, just filled the 2 cycle can a week ago.
 

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GANG GREEN GIZMOW KILLER!
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Try taking the cap off right after shutting it down.


The pressure does not build up, it just pushes the fuel out and floods the engine while sitting.


Some old chainsaws will actually boil the fuel and have a similar problem.
 

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Discussion Starter #5
Interesting! So is there a vent in the cap on that one, or is there a vent tube coming out of the top of the tank? Sounds like something is plugged up you think?
 

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Common problem.

Try a new plug, first. If the plug has alot of resistance, it can make hot starting nearly impossible, but will cold start fine.

Do a compression test..if the compressionis low when warm, it can also make for a hard time starting hot.
 

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Discussion Starter #7
Try taking the cap off right after shutting it down.


The pressure does not build up, it just pushes the fuel out and floods the engine while sitting.


Some old chainsaws will actually boil the fuel and have a similar problem.
I'm trying to get my head around this still, so is something plugged or did something wear out to cause this that I can replace, or is it just a bad design?

Ok, I think I get it, so is it the heat from the engine causing the fuel vapor in the tank to expand, which only happens when the engine is warm... I'm just thinking back to the outboard, when you forget to vent the tank, and after about 10 minutes the engine slows down and dies, and as your passengers start to get worried you twist open the vent and it sucks in a bunch of air and the tank pops back to its regular shape and the engine starts right back up.
 

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makin noise!
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have they had any maitenace done in thier life time?
i'm with Red, start by trying a new plug first.
 

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Discussion Starter #9
Not sure when I replaced the plug, before last season, probably the year before, but I cleaned it really good.

So Yesterday my 340 got passed from neighbor to neighbor for a good part of the day. Venting the cap worked perfectly, we had no warm starting issues.

Was this tank just made without a proper vent? I'm wondering if I should rig one up.
 

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GANG GREEN GIZMOW KILLER!
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Im not familiar with that machine, only the problem.



Check and see if the engine is not excessively dirty as this can be a symptom of an overheated engine.
 

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The pressure inside the tank is overcoming the limitation of the worn 'float' needle/seat. There is a very small fuel 'chamber' in a lot of two-stroke carburetors that is the equivalent of a float bowl. It is filled by the diaphragm being pumped by the changing crankcase pressure/relief as the piston goes up and down. If the fuel gets hot, the vapor pressure can be more than the normal operating pressure, and the 'float' equivalent can seep the fuel into the crankcase, and flood the engine. In some, the check valves that enable fuel to flow from the tank, and then into the carb 'chamber' can be overcome by this pressure. In the cheapest Walbro, the valves are gasket material flaps made when the gasket is cut.
tom
 

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Discussion Starter #12
I had guessed that it was from the flaps in the gasket getting worn, at some point here I'll order a new gasket, i guess the re-build kit and have at it. I clean my equipment off pretty often, I'll have to make sure there isn't any dirt hiding inside the plastic casing anywhere preventing airflow. For now, venting the cap seems to be working, though I did slosh some out when I picked it up to put it away Saturday, and I am concerned about crud getting in the tank when its sitting, so its not an ideal long term solution. Thanks all!
 

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Discussion Starter #13
Ok, now that I've been paying more attention, when I open the cap when I shut the machine down I do notice pressure being relieved. There is a tube coming out of the top of the tank that I would assume is supposed to be a vent. I took the tube out and tried to blow and suck air through the tube but could do neither. It looks clean... I tried scraping at the outside, there didn't appear to be anything built up on it. I suppose there could be something plugging it up from the inside, I guess I'll pull it off again and try cleaning out the inside. Can anybody confirm if logic prevails in this case, and this thing is supposed to allow the tank to breath? Also, any ideas what might have plugged it up?
 

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GANG GREEN GIZMOW KILLER!
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The tube should have a plastic funnel looking thing on the exposed end, this is your vent mechanism.


It should pass air one way. The little filter inside can get gummed up and blocked. Try cleaning it or just find a replacement.
 

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Discussion Starter #15
I'm about to order the vent for my BR340. I have the parts diagram for the 340 and am confident I have the right part number. 0000 350 5800. I was going to order one for my dad's BR320 as well, and for some reason I can't seem to find any info on the BR320. Does anybody know if thats the same part number?
 
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