Stihl backpack blower quits after running fine for a couple of minutes?

[callbay]

It is a model BR420C Magnum.

I already put on a new carb, air filter, fuel line, fuel filter, and I blew into the line that goes to the one way valve on top of the gas tank and it seems to be working. It also has new fuel/oil mix. I adjusted the new carb so it was running great till it quits. It still does the same thing as before I did all those things.

I have tried opening the gas cap and then it starts but just runs a few seconds.

Any help will be greatly appreciated.

Thanks guys!

 

[97prizm]

Does it bog down then cut out, or just stop?

 

[callbay]

It stops like it ran out of gas.

 

[mrsilv04]

Have you tested it for spark once it quits running? I'd suspect the coil.

Sometimes coils will quit once they get warmed up.

 

[97prizm]

From what I could find several websites said to check the tank vent, and pull the spark arrestor and blow torch it out.

 

[Escape08]

I cleaned the spark arrestor on my Homelite blower and ran fine. Maybe you need to look into that.

 

[andyd]

please post a follow up

 

[mk378]

Spark plug!

Also check that the wires to the kill switch are not shorting out. If you disconnect the small kill wire from the coil, the switch becomes completely inactive.

 

[SwampSurvivor]

Is it a 2stroke?

 

[stevejones]

is the "new carb" genuine STIHL or Amazon basics?

 

[DriveHard]

I second the tank vent...if that is plugged, you will starve it of fuel.

 

[callbay]

New carb was from Amazon but the old carb did the same thing as the new one.

I had already taken out the spark arrestor.

 

[Cujet]

I know this sounds silly, but you are mixing oil with the fuel, correct?

Does using the choke a bit, help it run longer?

One thing you can try is to reduce the spark plug gap to a tiny gap, and see if that helps. This can help troubleshoot coil and plug problems.

 

[Gyro Gearloose]

Go to Harbor Freight and get one of the $5 spark testers and narrow down the spark/fuel debate. I wasted days and even bought a second replacement carb chasing what I would have bet a paycheck was a carb problem only to put the tester on and find that the spark was cutting out.

 

[jhellwig]

Put in a new spark plug before messing with anything else. Cheap, quick and can cause the same symptoms as a fuel related issue.

 

[callbay]

I put in a new plug and no different.

It seems to loose it's gas prime so to speak. It won't start unless I pour a little gas in the plug hole and then it starts right up but it will start running bad and quit after just a few minutes.

I have a new gas filter and gas line installed, I tried it without the gas filter and no better. The one way valve to let air into the gas tank seems to work.

Thanks again, guys!

 

[RobertB]

I just chased this and found out that it was indeed the coil. Once it heated up, boom…done. Replaced it and all good. On a Stihl wacker.

 

[Brian123]

I just chased this and found out that it was indeed the coil. Once it heated up, boom…done. Replaced it and all good. On a Stihl wacker.

wacker! LOL

 

[ripcord]

Does this unit have a lot of hours on it? If yes and you can't figure it out, you might want to pull the muffler off it and have a look see at the piston and cylinder wall to check for scuffing or scoring. A bad piston and cylinder would make it harder to start, BTW.

I do like a previous poster's suggestion about disconnecting the kill wire. Also check it for rubbed through insulation. That will ground out the coil and kill it.

 

[super20dan]

its the coil most likely. also do a compression check.this is a very old blower and 2 strokes do strange thing when they start to wear out