Stihl BR 400 started to struggle and died after running fine

[d000hg]

I was given a BR 400 which had been well used but ran even after storage (with fuel!) for 2 years by a retired gardener.

Last winter it stopped running and I took it to an approved Stihl dealer for a service. Since then it's been used only a handful of times and has started impeccably.

Now I have deja vu, just as the leaves are falling this happens...

It starts cold, on idle after 2 pulls as normal and I use it for perhaps 20min happily. Then I hear it start to struggle a bit, lower revs and a bit uneven. I find that reducing the throttle a little helps, but a minute later the same. Over about 5 minutes this went round and round until all it would do is idle or struggle terribly - then it died. I restarted it easily but even on idle you could hear it slowing like a dying grandma until it stopped.

I am an engine noob with some basic knowledge but am guessing it's either related to air or fuel. Since it was serviced I've been using the Stihl pre-mixed non-ethanol fuel to avoid problems!

I have tools, are there any easy steps/tests I can do to see if it's an easy fix for losing it right when I need it (again)? Do the symptoms I describe suggest a particular problem?

Many thanks.

 

[Burnerman]

The first thing to do is to check the air filter.....if that is clean then I'd venture inside the carburettor.
However as this machine must have done a fair bit of work by now, I'd arm myself with a diaphragm / gasket set (two of each) and a can of aerosol carb cleaner before starting.
One diaphragm pumps the fuel to the carb (as there is no float chamber, but there is a needle valve) and the other is a metering diaphragm. Both have a gasket stuck to them which must be in the correct place, so do look for that.
For spares, either visit a Stihl dealer or look for the C1Q number on the side of the carb...differences in the carburettors are subtle.
No special tools are needed, use compressed air with extreme caution to avoid blowing out some welch plugs! Inside the carb is a very fine gauze filter that is often overlooked.
For the L and H adjustment screws, count how many turns in and then unscrew them - don't mix them up!
John

 

[d000hg]

Ha, the forum reminded me of my previous thread: https://www.diynot.com/diy/threads/stihl-leafblower-stops-running-just-in-time-for-autumn.490406/

So a curious development. I went out to have a look this afternoon and decided to try running it first. It started easily and just like yesterday it was fine for a few minutes then started losing power. Instead of just trying to push through it, I set it to idle in between use and found it seemed to 'recover' for short periods if I did this. I was able to use it for ~1 hour in total in this manner. Any time I ran it hard for a a little time it started struggling so I stopped using the throttle lock and used the trigger only as much as needed and actually got the job done (100m drive covered in leaves).

By the end of the time it actually seemed a bit better than when I started. So go figure... what on earth could be happening?

 

[Burnerman]

This is fairly typical really - the blower is using up the limited supply of fuel in the carburettor and then it tends to stall. Low revs allows the fuel to replenish to a degree, and off you go again.
As well as the carb filter there's also one in the tank.....chances are it will be as clean as a whistle.
The machine runs better when its warm as it can cope with a lean mixture.
For genuine Stihl carb gasket set, budget around 20 quid, much cheaper for pattern parts.
John

 

[Bilabong007]

Could also be building back pressure in the fuel tank.

If you open the tank and it fixes it for a while, the tank air inlet could be blocked

Just a thought

Graeme

 

[d000hg]

Could also be building back pressure in the fuel tank.

If you open the tank and it fixes it for a while, the tank air inlet could be blocked

Just a thought

Graeme

I was suggested this and gave it a try but it didn't seem to be the culprit, sadly as that would've been great!

 

[Burnerman]

Always a good move to do what Graeme suggests!
Although not usually a problem with back pack blowers, it certainly is with the BG series and as for the stone cutting saws, absolutely vital.
Not all machines have a tank vent though, some breathe through the carb. Vents can resemble a beehive shape in rubber, or a length of plastic tubing with a screw thread in the end.
John