Walbro WB37 tuning methods

There are lots of different methods for tuning the Walbro WB37 carb. Below is a selection giving the source, the original description and my rewriting it in point form to make it easier to compare them:

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Different methods

Southwest airsports method 2

Alex Valk method 3

Lars Sletten method 3

Matt Minyard method 6

Miroslav Svec method from facebook comment 8

Footflyer method 10

Bayne method 11

General information for WB-37 Carb

Note:

Refer to your manual to get the starting settings or the Safe Settings for your motor

Direction to turn:

Open is more fuel and is more rich and is anticlockwise
Close is less fuel and is more lean and is clockwise

Amount to turn:

Full turn is 60 minutes
Half turn is 30 minutes
Quarter turn is 15 minutes
One eighth turn is 7.5 minutes
One sixteenth turn is 4 minutes

Popoff pressure

Higher popoff pressure → lean and fuel starvation

Lower popoff pressure → rich

Metering lever heigh

Low lever → lean and fuel starvation

High lever → rich

Southwest airsports method

http://www.southwestairsports.com/ppgtechinfo/wb37/wb37.htmii

Restated in point form:

Start with the safe settings for H and L for your motor
Adjust idle to get 1900-2100prpm
To adjust H

Go to full throttle and lean it until the lean drop off (it is now running lean - do not run it for more than 10 secs like this)
Adjust H to get a safe operating temperature

To adjust L

Open or close L until you get max revs
Suddenly apply full throttle and do one of the following depending on what happens

If motor bogs down (it is too lean) then open L 4 minutes. Then repeat full power. Keep opening L until it does not bog down
If motor does not bog down then close 4 minutes and repeat until it .ol bog down (it is now too lean). Richen it a little until it does not bog down

You may need to readjust idle and repeat

Alex Valk method

http://inventions.aerocorsair.com/id36.htm

Restated in point form:

Adjust idle
To adjust L

Apply throttle slowly

If hesitates then richen L by a 7 minutes
If shakes then lean L

Readjust idle
Adjust H

Adjust until max RPM
Lean it until you get to the lean drop
Then richen to you get to Max RPM
Then richen so you get drop of 20 to 60 in RPMl

Lars Sletten method

http://www.flayhay.com/P r BB to all aramotor/walbro-forgasser/walbro-carburator-adjust-eng.html

And rewritten into point form:

Warm up to 100c on CHT
Set idle to 2000 to 2500

To adjust L

Test 1

Lean L until you get to max RPM
riched it until there is a 50 rpm drop in RPM
Note the position

Test 2

From idle

gradually lean L until there is a drop off and note the position
gradually richen until there is a drop off and note the position

The mid point between these is the best L position

Compare the two positions and they should be the same. If they are not the same then use the position from test 2
At this position the motor should respond quickly to quick throttle presses with no hesitation

To adjust H

Lean H until you get max RPM then richen it until you get a 150-200 RPM drop off.

If max RPM is over a big range then use the position where max RPM was first achieved
See if you can find lean dropoff and rich dropoff points and use the ½ way position

Then repeat set idle, L and H

See Lars Sletten advanced tuning page

http://www.flayhay.com/Paramotor/walbro-forgasser/advanced-carb-tuning.jpg

Matt Minyard method

https://www.facebook.com/groups/671524316192801/permalink/2458567787488436/

Restated in point form:

Set both to the starting positions (these are the safe settings for the Vittorazi Moster)

L 1/ 4 to 1/ 3 open or 15 to 20 mins
H 1 + 1/ 8 to 1 + 1/ 4

Adjust L

Very unlikely that you will damage motor by adjusting L
Squeeze full throttle as fast as possible and adjust it so it does not hesitate
If you find that you have to keep using throttle to stop it dying you are probably too lean
If it bogs when you quickly apply throttle it is probably too lean
If it has steady idle and does not hesitate when throttle quickly applied then the L is good

Miroslav Svec method from facebook comment

https://www.facebook.com/groups/671524316192801/permalink/1957891780889375

Restated in point form:

Use safe settings
Warm motor up
To adjust L

Apply throttle fast

If it revs up with no hesitation then lean it a fraction and repeat
If there is a slight hesitation then richen it by 2 minutes

Set the idle to 2200 to 2400
To adjust H

Method 1: Apply full throttle and wait for it to stabilize

If less than 8600 then you are too lean
If more than 8600 then you are too rich

Method 2 is based on plug colour but this can be inaccurate based on throttle setting that it was cut at.

Footflyer method

http://www.footflyer.com/walbro-carburetor-troubleshooting-tuning/

Rewritten in point form

Set both H and L to recommended safe settings
Warm up motor
To adjust H

Go to full throttle
Adjust H to get max RPM
Hold it at full throttle for about a minute
If the motor goes Learn you will need to richen L slightly
If this does not work then you need to adjust needle inside carb

If WOT runs well then we will adjust L to stop 4 cycling

Slowly release throttle until is starts 4 cycling then
Hold throttle here and adjust L so the 4 cycling barely stops
Then slowly release throttle a little and repeat to stop 4 cycling

Adjust L to stop hesitation

From idle apply throttle
If it bogs or hesitates then richen L slightly

Test that it is tuned correctly

It will run at any RPM and not 4 cycle
You will be able to idle and then apply throttle and it will not hesitate or bog

Bayne method

https://www.hunker.com/13404553/how-to-adjust-a-walbro-carburetor

Restated in points

Set starting positions
Warm up engine
To adjust H

Apply full throttle
Adjust H to get steady RPM

To Adjust L

Quickly depress throttle if hesitates then richen
If engine pops heavily at idle when coming down from full throttle" it is too rich and you should lean it