Arbtalk.co.uk | Discussion Forum for Arborists

Just a quick question, I know its not strictly chainsaw related...

Does anyone know the max RPM's of a Stihl BR400 backpack blower? I've currently got one running around 6200rpm - it's fourstroking a bit but it would be good to know if it can run any faster!

Have looked in the user manual but doesn't seem to mention it

Stihl don't give max RPM for blowers as, in their words 'the power is constantly being absorbed by the fan'
I've just checked this on the dealer system to be sure of my facts.

Thanks for going to the effort of checking for me Gardenkit .

Looks like i'll have to tune it by ear - I guess as it runs at lower rpm's to a saw that it is more tolerant to being 'near enough'???

Yep, the thing with the blower is that it is always under load, unlike most other 2t machines which have WOT speeds with no load.
We tune a saw, for example, to 4 stroke under no load, so that as the power is demanded it uses more of the excess fuel and reverts to 2 stroking.

The blower is always under load and so should not be fourstroking, so it needs to be weakened a bit, this will increase the revs. Check the plug colour after a bit of use, if its light coffee colour it is fine. If its white, then its too weak, and lean failure can result.

I just looked at every piece of Stihl literature I own including the service manual for the BR 400 .As has been pointed out they give no max RPMs .

I had heard it's around 8,000 rpm but I have no documentation to prove that as fact or fiction .FWIW though I own one and it's a nice unit .

Find the max rpm with a clean air filter, then richen it up so the rev's drop 50-100.

Had a feeling it shouldn't be 4 stroking - will lean it up a bit and then check the plug colour!

Like you say Al despite it being quite old now I also think the BR400 is a nice machine - not sure I like the new styling of the stihl backpack blowers, they look less 'industrial'!