How to set High speed on blower?

[Kneejerk Bombas]

How do you set the high speed on a blower? It's a BR400 and I have a tach.

 

[12guns]

have you tried setting it by ear? Being a blower, I would think you can get plenty close. I have an old Stihl BG60?? Something like that. It was given to me, after getting it to run, I was impressed how responsive the carb was to adjustment. When leaned out, it was obviously running too fast so I backed it off a bit and have had not problems since. When in use, I doubt you will be able to tell a diff of 10 mph. Just my .02. I'm sure you could use your tach as well, but the rpm's are over my head. Don't get me to lying.

 

[Kneejerk Bombas]

I set it by ear and it was a little hard for me because the blower is always under load. It seemed like trying to set a rev-limited coil saw by ear, I wasn't quite sure.
I did get a PM with the correct initial settings and RPM, I think, I just need to get to the shop and see what carb it has.

 

[Lakeside53]

No.... you can't set a BR400/420 blower by ear.... as the device is under full load, there is no "ear sound" that gets you even close.

Set the screws to 1 turn out (assuming you have an HD4 carb). Start it, warm it up for a few minutes. Lock the throttle to full output, wait a minute or two for it to get really hot.

Turn the H screw in (leaner) slowly until the rpm peaks, then back it off until it falls about 50-75rpm.... You can set it closer, but I wouldn't... You are now running just to the rich side of peak EGT.

If your blower is in GREAT shape - it will pull maybe 7500 rpm. If average, 7000-7200...

It has no rev limiting coil.. What you hear is it falling off a cliff when the mixture gets too rich, or worse, if too lean it's just not getting enough gas for the load and is overheating.

 

[12guns]

No.... you can't set a BR400/420 blower by ear.... as the device is under full load, there is no "ear sound" that gets you even close.

Set the screws to 1 turn out (assuming you have an HD4 carb). Start it, warm it up for a few minutes. Lock the throttle to full output, wait a minute or two for it to get really hot.

Turn the H screw in (leaner) slowly until the rpm peaks, then back it off until it falls about 50-75rpm.... You can set it closer, but I wouldn't... You are now running just to the rich side of peak EGT.

If your blower is in GREAT shape - it will pull maybe 7500 rpm. If average, 7000-7200...

IT has no rev limiting coil.. What you hear is it falling off a cliff when the mixture gets too rich, or worse, if too lean it's just not getting enough gas for the load and is overheating.

When adjusting mine, there was a very audible difference as I adjusted at full throttle. That's what I was refering to, after increasing rpms, I backed off a bit, worked fine for me. You may not be able to hear it "4 stroke" and all that, but you can hear a difference and should be able to tell when it's running too fast.

 

[Lakeside53]

When adjusting mine, there was a very audible difference as I adjusted at full throttle. That's what I was refering to, after increasing rpms, I backed off a bit, worked fine for me. You may not be able to hear it "4 stroke" and all that, but you can hear a difference and should be able to tell when it's running too fast.

Unfortunately you can't hear a 50 rpm drop on a BR400... By the time you hear it drop it's way too rich and you get into other problems.

 

[bwalker]

Lake is right, it doesnt take much to fubar a blower due to the load involved.

 

[ol'homey]

No.... you can't set a BR400/420 blower by ear.... as the device is under full load, there is no "ear sound" that gets you even close.

Set the screws to 1 turn out (assuming you have an HD4 carb). Start it, warm it up for a few minutes. Lock the throttle to full output, wait a minute or two for it to get really hot.

Turn the H screw in (leaner) slowly until the rpm peaks, then back it off until it falls about 50-75rpm.... You can set it closer, but I wouldn't... You are now running just to the rich side of peak EGT.

If your blower is in GREAT shape - it will pull maybe 7500 rpm. If average, 7000-7200...

It has no rev limiting coil.. What you hear is it falling off a cliff when the mixture gets too rich, or worse, if too lean it's just not getting enough gas for the load and is overheating.

Lake,
What would the compression psi on a BR400 be for great and average shape? Also do you ever replace the blower fan wheel due to normal wear (no broken fins)? I ask because I'm wondering if a worn fan could cause the RPM's to go high due to the decrease in load?

 

[Lakeside53]

Compression of 155-165 will run the engine at about 7400->7500... Around 145 it's geting down to 6900-7100...

I've never seen a fan in a Br400/420 worn to the point it causes an overspeed condition.. In fact, I rarely see wear in there - they do get a lot of crap stuck on them, but..