LO206 carburetor settings

steve baker

Member
We have been receiving a lot of calls about what are good settings for the Walbro PZ22 LO206 carb. Based on what we have found I am going to list them below as good starting points and will probably be fine for 90% of the times for Senior classes and for the green and yellow slides the only difference is we set the C-clip needle on slot #2 from the top.

Float height = .860 / .880 inch
Float drop = 1.050 inch
Idle air bleed screw = 1 turn out
C- clip needle setting = middle slot ( #3 slot )

Additional tech info from Briggs..........http://www.briggsandstratton.com/engines-racing/~/media/Racing/carbtuningguide.pdf

Steve
www.Bakerracingengines.com
 
Float height = .860 / .880 inch
Float drop = 1.050 inch
Idle air bleed screw = 1 turn out
C- clip needle setting = middle slot ( #3 slot )
How do you compensate for changes in air density? Knowing a 5% change in the air density would mean about a .001" change in the main jet. I'm assuming the stock main jet is .039". Is there a tolerance on the size of the main jet? Seems like I read somewhere that there is a tolerance on the size of the main jet. I don't remember exactly, but I think it was plus or minus .001". Did you know that going from .038" to .040" is a 10.85% change in area?
 

steve baker

Member
How do you compensate for changes in air density? Knowing a 5% change in the air density would mean about a .001" change in the main jet. I'm assuming the stock main jet is .039". Is there a tolerance on the size of the main jet? Seems like I read somewhere that there is a tolerance on the size of the main jet. I don't remember exactly, but I think it was plus or minus .001". Did you know that going from .038" to .040" is a 10.85% change in area?
In general I agree with your calculations Al.......do you know how a 5% change in air density would affect lap times and then if you would correct the main jet to match the 5% air density change would again affect the lap times............please make that calculation for me based on a 1 mile long track with 10 right turns and 3 left turns. Im not sure what the factory tolerance is for the main jet hole size is but the Briggs rule set are ........... Main jet – #95, hole size is .0380” 0.036 go, 0.039 no go.

But for now i'm off to the local races.

Steve
 
.036" to .039" jet size equals a 17.4% change in area. What if you get to the track, and based on previous experience, the observed air density calls for a .039 jet. What do you do if the air density goes up even higher?
 

steve baker

Member
.036" to .039" jet size equals a 17.4% change in area. What if you get to the track, and based on previous experience, the observed air density calls for a .039 jet. What do you do if the air density goes up even higher?
Lower the needle C clip, turn the idle air bleed screw in and or raise the float height, all of these changes will result in a richer F/A ratio to help match the higher air density levels. These adjustments will more than make up for the max air density that we would have any where planet earth.

Steve
 

CarlsonMotorsports

Premium User
Yep, that's right, Steve. I have yet to see where I can't get the a/f ratio where it needs to be on a 206 with a fixed jet, by simply changing the e-clip and/or float height. I generally don't mess with the air bleed (other than at idle - set it and leave it alone.) I hear of guys who are reworking the stock 95 jet within the rules and am wondering why (is there an advantage to getting the fuel closer with the main rather than the other adjustments we have on these carbs?) On an alcohol carb we change the main first because of the volume needed, then fine tune with the other items...Isn't that exactly what we're doing with the 206 (fine tuning?) Seems to me, anyway. :)



-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
26 years of service to the karting industry
765-339-4407
bcarlson@CarlsonMotorsports.com
--
 

Kimball

New member
How much to adjust float level

I just bought my first 206 engine for my son and wanted to make sure the settings were correct. Although I did not check the main jet size while I had the carb open I did measure the float level which seemed to be way off. With the carb inverted I measured it at .700 and the clip was in the second position. Our altitude here in Centennial is 5800' so it would make sense to lean things out. I often hear you guys mention adjusting the float level and clip to made necessary adjustments but how much is the right amount. I realize it's not an exact science and there are other factors so right now I'm just looking for a starting point for the float and clip position.

Thanks,
David
 

CarlsonMotorsports

Premium User
If you've already measured it at .700", I am assuming you already have a way to accurately measure float height.
Simply bend the tab under the floats that rests on the inlet needle and remeasure. Be sure to bend the tab with a small bladed screwdriver...do not bend the floats themselves. AND, try your best to keep the two floats even/equal in height.
As far as where to set it -- you might try .810" or so and the middle clip on your needle then go from there. There's a lot more to it than simply setting the floats a specific height by your altitude. Realistically you will tune the engine leaner than someone at sea level, but how much leaner depends on more than just your elevation. For instance, we often consider the track configuration, length of longest straight, highest G corner, smoothness of track -- all can have an affect on your final tune. Even tuning them on the dyno with an a/f meter isn't the final answer most of the time for the above reasons.
Be sure to check out the Briggs videos online, as well as the PZ tuning guide.


Also...check with your local rules -- There is a track out there somewhere that allows you to change the main jet to a 93..if that's the case, then you'll be starting all over again.

-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
28 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
With the carb inverted I measured it at .700 and the clip was in the second position. Our altitude here in Centennial is 5800' so it would make sense to lean things out.
http://www.longacreracing.com/instructions.aspx?item=8024
Follow this link and read the instructions they give for using an air density gauge. When I raced, I considered the air density gauge a necessary item!!

Longacer says a 1% change in air density calls for a 1% change in fuel supply. With a .038" jet to start, if you go to a .039" jet, that's a little more than a 5% change in area. The air density would have to go up five points to justify that big a change in jet size.

It would be great if somebody who has an air density gauge could tell you what jet they run at what air density. If you had an air density gauge, you could easily calculate the jet size for your area.

I've been told many times that these little engines do not respond to changes in air density, but if that was true, you wouldn't be looking for the right jet for your altitude.

The way I look at it, most dyno data acquisition systems say right on the printouts "corrected torque and horsepower". They do that because they know that horsepower varies with barometric pressure and temperature. Air density is a measure of how much barometric pressure is affected by temperature. If either one goes up or down, the air density changes.
 

Elmer Patterson

New member
Ive posted this befor I set my Jr 1 carb at 870 for our local track sometimes a bit less (885) when temps rise and air drys out at our elevation of 2500 feet .We also race at other tracks where the elevation is aprox 100 feet . Due to fixed jet sizes and floatheight ,air density and temperature. We start fast out of the gate. Win Win
 

Kart43

Member
It would be great if somebody who has an air density gauge could tell you what jet they run at what air density. If you had an air density gauge, you could easily calculate the jet size for your area.

I've been told many times that these little engines do not respond to changes in air density, but if that was true, you wouldn't be looking for the right jet for your altitude.
Al what this person would or should be told is you have to run a #95 jet unmodified, this is a set rule. If you do run anything else, or it can be proven that you have removed material you are operating outside of the rules. An air density gauge for jet sizing when running Briggs and Stratton rules is not needed. Now if you want to build a pipe with a Lamba gauge to tune A/F by means of needle clip and float height in the pits, remove and install an unmodified pipe before you race that would be beneficial. Frankly there is not time between on track sessions for most of the required tuning.
 

Gonzari

Member
We put on an engine clinic @ Monterey CA the first weekend in Feb. Here's a picture of the tool used,mounts using the existing head bolts. Enough room under the tool to allow some scraping of carbon without having to disassemble.

 
Al what this person would or should be told is you have to run a #95 jet unmodified, this is a set rule.
That contradicts my understanding of the rule. In any case, I can't believe one jet can be right for the guy at sea level and the guy at 5000 feet!

In any case, I would be doing a lot of legal things to change the mixture ratio. I don't know all of what is legal, but I would certainly be exploring all the possibilities.

I believe rules that prevent you from tuning your engine to the prevailing conditions are ludicrous.
 

XXX#40

Member
That contradicts my understanding of the rule. In any case, I can't believe one jet can be right for the guy at sea level and the guy at 5000 feet!

In any case, I would be doing a lot of legal things to change the mixture ratio. I don't know all of what is legal, but I would certainly be exploring all the possibilities.

I believe rules that prevent you from tuning your engine to the prevailing conditions are ludicrous.
if everyone has to follow the rule on the jet how is that not a level playing field?
 

Kimball

New member
Confused on float height for altitude

As far as where to set it -- you might try .810" or so and the middle clip on your needle then go from there.
Be sure to check out the Briggs videos online, as well as the PZ tuning guide.
I think I'm getting confused on something. At my altitude of 5600' I want to lean the carb out to match the lack of air so that means I want LESS fuel in the bowl (I think). It seems that with a higher float level value like .900 it would stop the flow of gas sooner with the result of less fuel in the bowl. If I set it to .810 the fuel would be deeper in the bowl. Am I backwards?

Also where do I find the PZ tuning guide of which you speak. I thought I had watched ALL the B/S videos.:confused:
 
I think I'm getting confused on something. At my altitude of 5600' I want to lean the carb out to match the lack of air so that means I want LESS fuel in the bowl (I think). It seems that with a higher float level value like .900 it would stop the flow of gas sooner with the result of less fuel in the bowl. If I set it to .810 the fuel would be deeper in the bowl. Am I backwards?

Also where do I find the PZ tuning guide of which you speak. I thought I had watched ALL the B/S videos.:confused:
Are you saying they don't allow jet changes to compensate for that altitude? I wonder why they would do that and still allow you to change the float bowl level, a much more difficult task than changing a jet!
 

steve baker

Member
I think I'm getting confused on something. At my altitude of 5600' I want to lean the carb out to match the lack of air so that means I want LESS fuel in the bowl (I think). It seems that with a higher float level value like .900 it would stop the flow of gas sooner with the result of less fuel in the bowl. If I set it to .810 the fuel would be deeper in the bowl. Am I backwards?

Also where do I find the PZ tuning guide of which you speak. I thought I had watched ALL the B/S videos.:confused:
Kimball , Yes your correct, a .900 setting is leaner than a .810 setting. Also you might consider mounting a O2 sensor in a back up header and the appropriate data acquisition hardware to properly understand what your air fuel ratio really is! We use this equipment on our Dyno and it's not always what you think it should be. Mass produced parts do have some variation in them.............

Steve
www.Bakerracingengines.com
 
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Kart43

Member
I think I'm getting confused on something. At my altitude of 5600' I want to lean the carb out to match the lack of air so that means I want LESS fuel in the bowl (I think). It seems that with a higher float level value like .900 it would stop the flow of gas sooner with the result of less fuel in the bowl. If I set it to .810 the fuel would be deeper in the bowl. Am I backwards?

Also where do I find the PZ tuning guide of which you speak. I thought I had watched ALL the B/S videos.:confused:
You are actually correct in this .900 will cause a leaner condition than .810. The larger the measured float height while the carb is upside down reduces the fuel level in the bowl. http://www.ccwthariders.com/uploads/9/7/7/9/9779070/pz_carb_tuning_manual.pdf
 

Jimbo

If you talk the talk you should walk the walk
Kimball both you and Kart 43 are correct.
There will be less fuel in the bowl with a float setting of .900" than .800":rolleyes:
 
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