Stumped on Stihl BR450 Blower Stopping

[lehman live edge slab]

Thanks for the last couple of replies. I have replaced the coil and plug. There was nothing wrong with the original coil. I am convinced the issue is not ignition related. Earlier, I mis-spoke about the fuel/oil ratio. I have only ran 50:1 ratio. I used to have a Lawn Boy mower that was 32:1, and had it on my mind I guess. Last weekend I installed the Stihl carb kit, which consisted of the diaphragm and the piece of film on the other side of the carb that has the two little flappers for the crankcase pulses to pump fuel. The blower ran normally. Yesterday, I ran it and it had the issue again. I found that I could jump up and down, and shake the blower from side to side on my back, and get it to pick up power again. The neighbors probably thought I was crazy. Some times I did have to let it get back down to idle, to let the fuel supply catch up it seemed, and once or twice it stalled out, but I was able to get all the work done that I needed, where before, it would starve out completely and not re-fire for awhile.

Sounds like faulty vent to me, shaking the blower would pressurize the tank to a point. I’m leaning towards tank vent and of filter. I’m sure you changed filter but question is was it oem or aftermarket? Some cheap filters don’t flow properly and or come apart inside.

 

[HusqvarnaDave]

I have a BR450 that I purchased new in 2018, which has performed flawlessly until recently. I am a homeowner who uses it once a week during the summer months, after mowing, and multiple times during the Fall leaf season. I do not believe it is "worn out", like piston rings, crankcase seal, etc. I've always ran 93 octane gas, mixed at 32:1, with the recommended amount of Sea Foam in the mix to keep it clean. I've kept a clean air filter in it. The issue is that, from cold, it will crank up and run as normal, but after 5-10 minutes of wide open throttle blowing, it will quit running. I checked the screen in the muffler, and it is clean. I replaced the fuel filter and gas tank vent. I replaced the coil and the spark plug. None of these things helped. I've removed the plug during these events, and it's dry. My gut feeling is that it's the carburetor, for whatever reason not keeping fuel in the "bowl". I replaced the carburetor, and it ran as normal for a couple of weekend uses. Thinking the problem is solved, but no, the next use it died again after probably 10 minutes. When it does this, it might re-crank once or twice, but will not throttle up wide open, and eventually it won't crank at all. Fuel can be moved using the priming bulb as normal. There is no debris blocking air flow and nothing obstructing the cooling fins on the cylinder, so I don't think it is an overheating issue. The fuel line itself is about the only thing I haven't replaced, but it is supple and looks ok. Any advice is appreciated.

Sounds to me like your fuel tank vent is plugged, the blower runs as it should until it draws enough fuel out to cause a vacuum inside the tank.
To check this, simply crack open the fuel filler cap after it's died, and see if it will restart.
Best of luck..

 

[lehman live edge slab]

Well, getting back to basics here... Next time it wigs pull the plug immediately, put it in the plug wire, ground the threads, switch on, pull the rope and check for spark. No spark, maybe buy a new oem coil or replace sparkplug. Replace every single fuel line and the impulse line with oem rubber lines. Make sure your air filter is in good shape. Pull the muffler and make sure your engine's exhaust port is not loaded with carbon, remove the spark arrestor screen and clean if necessary. 32:1 is a lot of oil for a 4-mix engine. I know a lot of people recommend more oil, but unless you are running a very thin oil 50:1 should be fine. 40:1 max for thin oils. Outboard motor oil "maybe" 32:1. I have been running 4-mix engines for 20 years so I've been there done that. They are not 2 stroke engines and they just cannot gobble oil like many 2 strokes can. Lay off the Seafoam for a while. Any aftermarket parts replace with genuine Stihl oem. I realize I repeated what you have replaced but what I have seen is a bad tank vent so consider oem if not. Air, airtight, airflow, fuel, compression, spark. Most Stihl mechanics will say to never use aftermarket carbs and coils. Oh.... good ngk plug with proper gap. bpmr7a @ .020. Sorry if I left things off, but that's s lot.

The 350/450 are 2-mix engines right around 60cc can’t remember exactly what cc just low 60’s.

 

[Mike W]

The blower has continued with the intermittent issue of seemingly starving for fuel at throttle. This weekend I installed a Stihl OEM tank vent. Also, the only section of the fuel line I haven't replaced is the piece inside the tank, which appears to a be sold with the white plastic piece that snaps into the tank for the fuel/primer bulb return connections. In my humble opinion, the price for this part is unreasonable. I inspected the white plastic piece and cut 1/4" off of the top of the hose, to make the prong seal in a new location, in case it might be sucking air at the inside the tank connection. Also, shaking the blower would slosh gas at the connector, so maybe it picks up fuel? These two steps did not change the symptom. I ran it today with a topped off tank, and it started acting up when I ran 1/2"-3/4" out of it, and I immediately filled the tank back up and tried again, but it continued to not be able to take throttle. Thinking back, the symptoms have never occurred until the engine is hot, but I find it hard to believe that the crankcase seals are causing the pulses that pump the gas to be too weak. But I have also just about run out of parts to swap and ideas to try.

 

[Mike W]

I couldn't feel any play in the crankshaft bearings, so I have a set of crankshaft seals and a tube of Dirko on order. Wish me luck.

 

[MtnHaul]

I'm very curious as to what the final verdict/culprit will turn out to be. I have 2 BR450 blowers and one is at least as old as yours and all I've had to do is replace an air filter or two and a spark plug. Actually now that I think about it I did have a problem with the wiring inside the rubber spark plug boot. It's been a long time but I think I had to pull the boot off the wiring and redo the connection between the stranded wire and the metal coil portion that snaps onto the spark plug. Good luck.

 

[Mike W]

I'm very curious as to what the final verdict/culprit will turn out to be. I have 2 BR450 blowers and one is at least as old as yours and all I've had to do is replace an air filter or two and a spark plug. Actually now that I think about it I did have a problem with the wiring inside the rubber spark plug boot. It's been a long time but I think I had to pull the boot off the wiring and redo the connection between the stranded wire and the metal coil portion that snaps onto the spark plug. Good luck.

Got it broke down today, the seals should arrive on Monday.

 

[hacskaroly]

Got it broke down today, the seals should arrive on Monday.

Do the bearings spin freely? Definitely a good time to spray them out and get them lubed. I have my Husky 365 split apart right now, waiting for bearings and seals...learned the hard way not to trust existing ones on a saw that I don't know the history!

 

[Mike W]

Do the bearings spin freely? Definitely a good time to spray them out and get them lubed. I have my Husky 365 split apart right now, waiting for bearings and seals...learned the hard way not to trust existing ones on a saw that I don't know the history!

I think I’m going to purchase new bearings. They do spin freely. One of them came off of the crank while I was checking, but I thought they were pressed on? There is some slight radial slop in both, but of course I don’t have fresh bearings to compare with. For the cost involved, I think I’ll replace them.

 

[hacskaroly]

but I thought they were pressed on?

Yes, they are pressed on, should not easily slide on/off.

 

[Mike W]

I installed new bearings and seals on Thursday, let the Dirko cure for a couple of days, and put the blower back together today and ran it. It was running good, but about 1/3 of a tank in, it started losing power again. It's hard to describe, but it is losing power slower than before, and if I let it idle for a bit, it will run normally again. I was getting less frequent "power loss events" than before, so I do think it made a change. But of course, the underlying issue remains. What I noticed with the bearings is, like I said earlier, one of them pulled off of the crankshaft by hand. Also, the crankshaft was shiny where the loose bearing sat. I had to drive the other bearing off, as expected. I placed that bearing on the "problem" side by hand, and I couldn't push it on. Since I could push the problem bearing on or pull it off by hand, I thought maybe the one bearing was bad. Both of the original bearings spun freely. I heated the new bearings up to 250F, and used a socket to drive them on the crankshaft. The problem side didn't require much driving, so I assume there is some wear on the crankshaft. It's a shame for a 7 year old machine. Looks like I'll be buying an Echo.

 

[lehman live edge slab]

I installed new bearings and seals on Thursday, let the Dirko cure for a couple of days, and put the blower back together today and ran it. It was running good, but about 1/3 of a tank in, it started losing power again. It's hard to describe, but it is losing power slower than before, and if I let it idle for a bit, it will run normally again. I was getting less frequent "power loss events" than before, so I do think it made a change. But of course, the underlying issue remains. What I noticed with the bearings is, like I said earlier, one of them pulled off of the crankshaft by hand. Also, the crankshaft was shiny where the loose bearing sat. I had to drive the other bearing off, as expected. I placed that bearing on the "problem" side by hand, and I couldn't push it on. Since I could push the problem bearing on or pull it off by hand, I thought maybe the one bearing was bad. Both of the original bearings spun freely. I heated the new bearings up to 250F, and used a socket to drive them on the crankshaft. The problem side didn't require much driving, so I assume there is some wear on the crankshaft. It's a shame for a 7 year old machine. Looks like I'll be buying an Echo.

Everyone can have a defective machine because of some bad tolerance parts from an outside source. Buy what you like and think is the brand you want but any of them at 7 years old could develop an issue and none of them will be under warranty at 7 years old, Stihl is 4 echo is 5 and husky is 5 I think.

 

[EFSM]

I installed new bearings and seals on Thursday, let the Dirko cure for a couple of days, and put the blower back together today and ran it. It was running good, but about 1/3 of a tank in, it started losing power again. It's hard to describe, but it is losing power slower than before, and if I let it idle for a bit, it will run normally again. I was getting less frequent "power loss events" than before, so I do think it made a change. But of course, the underlying issue remains. What I noticed with the bearings is, like I said earlier, one of them pulled off of the crankshaft by hand. Also, the crankshaft was shiny where the loose bearing sat. I had to drive the other bearing off, as expected. I placed that bearing on the "problem" side by hand, and I couldn't push it on. Since I could push the problem bearing on or pull it off by hand, I thought maybe the one bearing was bad. Both of the original bearings spun freely. I heated the new bearings up to 250F, and used a socket to drive them on the crankshaft. The problem side didn't require much driving, so I assume there is some wear on the crankshaft. It's a shame for a 7 year old machine. Looks like I'll be buying an Echo.

i was rereading some of your posts. I want to make sure I have this straight. You tried rebuilding the original carburetor and installing an aftermarket, but not a new OEM carburetor? I suspect that your problem is the accelerator plunger oring in the original carburetor, which will cause all manner of issues if it is hardened.

 

[Mike W]

i was rereading some of your posts. I want to make sure I have this straight. You tried rebuilding the original carburetor and installing an aftermarket, but not a new OEM carburetor? I suspect that your problem is the accelerator plunger oring in the original carburetor, which will cause all manner of issues if it is hardened.

Yes, I replaced the OEM carb with a carb from Amazon (which would have corrected the problem, if it were carb related), then I rebuilt the OEM carb with parts from Amazon, and I rebuilt the OEM carb with parts from the Stihl dealer. The “accelerator plunger o-ring” doesn’t ring a bell, do you have a pic?

 

[EFSM]

Yes, I replaced the OEM carb with a carb from Amazon (which would have corrected the problem, if it were carb related), then I rebuilt the OEM carb with parts from Amazon, and I rebuilt the OEM carb with parts from the Stihl dealer. The “accelerator plunger o-ring” doesn’t ring a bell, do you have a pic?

It is behind the throttle shaft.

 

[Mike W]

It is behind the throttle shaft.

It appears that the throttle cable only opens the butterfly, and the spring on the carb returns it. Is this o-ring accessible if you remove the butterfly and shaft?

 

[Mike W]

This is a pic I found, it is not the exact BR450 carb, but it is the same style. The pic didn’t come with descriptions, but 14 & 16 are what I was concerned with replacing. Mainly 16, which has the two little flaps that the crankcase pulses cause to pump fuel to the bowl side of the carb. Where is the o-ring located?

 

[EFSM]

It’s not on that diagram; it’s possible yours doesn’t have it. Stihl uses them fairly randomly. It is in a blind hole drilled above the one mounting hole on the engine side with a spring and a little piston and oring that are moved by a flat spot on the throttle shaft. When the throttle is pulled, it forces extra fuel into the high circuit; therefore, when the oring is bad, it allows air to be pulled into the high side or the metering chamber, depending on the primer setup. This attached photo is from a 550; again, maybe yours doesn’t have it. Most people have no idea this is on many Stihl carburetors.

 

[Mike W]

It’s not on that diagram; it’s possible yours doesn’t have it. Stihl uses them fairly randomly. It is in a blind hole drilled above the one mounting hole on the engine side with a spring and a little piston and oring that are moved by a flat spot on the throttle shaft. When the throttle is pulled, it forces extra fuel into the high circuit; therefore, when the oring is bad, it allows air to be pulled into the high side or the metering chamber, depending on the primer setup. This attached photo is from a 550; again, maybe yours doesn’t have it. Most people have no idea this is on many Stihl carburetors.

View attachment 478892

On the engine side, my carb only has the one hole for the crankcase pulses. I’d love to be able to fix the issue with such a simple method, but no such luck.

 

[EFSM]

Does the primer bulb fully fill with fuel?