Stihl Backpack Blower BR420 Magnum

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AlabamaDan

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Hi! I hate to just jump in and my first post is a plea for help. Please forgive me. I have a Stihl 420 Magnum Backpack Blower and I'm trying to get it running again, my son's no longer around to rake. It will turn over and tries to run, but it doesn't quite get there.

Today I removed the carb and soaked it for two hours in Berryman's Dip, you know the 1 gallon can. The air filter looked new and the spark plug looked pretty close to new.

The fuel lines are still flexible and don't appear to be damaged. If there is a little fuel filter in the tank, I didn't check it...

I did put fresh gas/oil mixture in it.

I set the kill switch to the up position (I).

If I set the throttle to wide open and fiddle around with the choke it will crank and run for a second and then die.

Ideas?

Thanks for the help ahead of time. :)
 
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Darryl G

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Hi from Connecticut and welcome to the forum. I'm a landscaper who obviously has heavy reliance on blowers. So I'm not one of the experts here but I've picked up a thing or two about getting and keeping small engines running.

Soaking the carb may not be enough. Sounds like you may have a plugged jet. You can strip a twist-tie and use the wire to carefully ream it out. Do you have ethanol in your gasoline there? I've had equipment accumulate an ethanol/water emulsion in the bottom of the tank during storage that fouled the fuel filter. And yes it should have one inside the tank. I hook the inlet line with a bent wire. I'd certainly replace it. I always replace the plug too for any starting/running issue rather than clean them. The first thing I do is dump fuel and replace with fresh, clean/replace air filter, replace spark plugs, clean the carbon from the muffler screen (I hold with pliers and torch with a lighter then brush off) and replace fuel filter. It's all about eliminating potential causes.

The mechanics here can offer a lot more detailed diagnostic info to help you get your blower running. Several make their daily rounds here.
 
Boudreaux In Eunice La.

Boudreaux In Eunice La.

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Hey Dan.......... What you gonna do besides Hey I'm from LA and I have a blower that runs good, but I'll be back in a week or so if it goes out ... LOL Are you from LA ????

I am but not Los Angry and Lower Alabama, but Louisiana......... I have spent some money in Bayou La Batre though,,, I had a bar room there ....

You have 2 adjustments on your carb if i'm right .......... L and H jet's ..... When you soaked the carb was your metering diaphragm still really soft or was it stiff ???? That makes a world of difference .... Also the pump side diaphragm should be in order....

Go ahead and see if you can locate the fuel filter in the take and check it.. Those should be changed once a year....

Does it run on choke pretty good ??? Or half choke ???


Let us know Mon Ami ~!~!
 
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AlabamaDan

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Boudreaux In Eunice La. said:
Hey Dan.......... What you gonna do besides Hey I'm from LA and I have a blower that runs good, but I'll be back in a week or so if it goes out ... LOL Are you from LA ????

I am but not Los Angry and Lower Alabama, but Louisiana......... I have spent some money in Bayou La Batre though,,, I had a bar room there ....

You have 2 adjustments on your carb if i'm right .......... L and H jet's ..... When you soaked the carb was your metering diaphragm still really soft or was it stiff ???? That makes a world of difference .... Also the pump side diaphragm should be in order....

Go ahead and see if you can locate the fuel filter in the take and check it.. Those should be changed once a year....

Does it run on choke pretty good ??? Or half choke ???


Let us know Mon Ami ~!~!
Click to expand...

Hi! I'm very familiar with Mobile in LA, but from UA. Louisiana is one of my favorite states. Thanks for the reply. I didn't disassemble the carb, but soaked it whole. That has worked for me on several other machines. I try not to disassemble carbs if I can get away with it. They tend not to run well after "I" do that. It's a last resort for me.

It doesn't seem to run no matter what position the choke is in. However, I have read that this model, while highly regarded as a great engine, tends to flood easily and should only be closed barely and rarely. Sounds like I may need to pull the plug and check for fuel in the cylinder.
 
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AlabamaDan

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Darryl G said:
Hi from Connecticut and welcome to the forum. I'm a landscaper who obviously has heavy reliance on blowers. So I'm not one of the experts here but I've picked up a thing or two about getting and keeping small engines running.

Soaking the carb may not be enough. Sounds like you may have a plugged jet. You can strip a twist-tie and use the wire to carefully ream it out. Do you have ethanol in your gasoline there? I've had equipment accumulate an ethanol/water emulsion in the bottom of the tank during storage that fouled the fuel filter. And yes it should have one inside the tank. I hook the inlet line with a bent wire. I'd certainly replace it. I always replace the plug too for any starting/running issue rather than clean them. The first thing I do is dump fuel and replace with fresh, clean/replace air filter, replace spark plugs, clean the carbon from the muffler screen (I hold with pliers and torch with a lighter then brush off) and replace fuel filter. It's all about eliminating potential causes.

The mechanics here can offer a lot more detailed diagnostic info to help you get your blower running. Several make their daily rounds here.
Click to expand...

Thanks for the replay. Connecticut is a beautiful state. I drove through there a couple years ago and it is really pretty country up there. Back to my problems. I plan to fish the filter out of the tank today and clean the muffler screen. I don't have a filter, but I could go with out a filter for testing couldn't it?

It's been sitting for a 3-4 years - with an empty tank. I seem to recall that it I took it to the mechanic and they tuned it up (lazy) because it wasn't running well. I couldn't get it to run then and just bought an electric one at a yard sale. That is now dead so I'm back to this old Stihl. Back then I did run regular ethanol gas, but I've since switched to 100% gas for my small engines. That tune up is the reason I didn't replace the spark plug. I figure if the filter still looks brand new and was replaced at the same time as the spark plug then it should be good too.

I'll try the screen (which I knew nothing about,) the in-tank filter, and pulling the plug to check and see if I flooded it today. Thanks for the advice guys.
 
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ILENGINE

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Since Darryl brought up the muffler screen. If you have one with the round exhaust hole, make sure it hasn't been filled with mud from the dirt dauber. also there is an internal screen inside the carb that can get plugged preventing fuel flow Normally will present itself with primer type carbs when you push the primer bulb down and it either is slow to come back up or doesn't come back up at all.
 
Boobala

Boobala

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AlabamaDan

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Where exactly is this spark arrestor screen?
 
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AlabamaDan

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Part #28. I may not have it anymore. PO may have taken in out already.
 
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