How to properly check float level?

[webbch]

I see it frequently recommended to check the float level before doing any other tuning related to the carb as it affects the fuel mixture greatly. The test consists of connecting a clear plastic tube to the carburetor drain valve, opening the drain valve, then turning on the fuel supply. The objective is to verify that the fuel line in the plastic tubing reaches a certain height, which represents how high the float went up before shutting off the flow of fuel into the bowl.

To that end, could someone please clarify the appropriate level to which I should see fuel in the clear plastic tube when I turn the fuel valve on?

http://img.photobucket.com/albums/v708/webbch/Carb03_zps42b3a0f8.jpg (http://smg.photobucket.com/user/webbch/media/Carb03_zps42b3a0f8.jpg.html)

In the pic, my understanding is that you want the fuel level somewhere between the red and yellow lines. The red line is the parting line between the carb body and the float bowl. In the last 2 carbs I've worked on, I've been having a heck of a time to achieve this - they've wanted to go up around the green line.

When I start out, I try to set the floats roughly parallel to the carb body and adjust from there if the above test doesn't put me where I need to be. If you adjust the float to put more pressure on the float needle to shut off the fuel flow, and observe no lowering of the fuel level, is the only conclusion to be drawn from that test that the float needle seat is worn out? Assume the carb was previously thoroughly cleaned out. Thanks.

[barnett468]

Different carb and engine combos use different settings. Some of the Kawi street bikes use a level similar to the green line.

I set the bikes like yours to the level I suggested on your other thread which is anywhere between the red and yellow line. Your red line is slightly high in the pic.

This is the level I have seen it come to when the floats are properly adjusted according to the factory spec which is measured in the actual float height.

This is also the method and spec I have seen in at least 1 of the 80's Yamaha 3 wheeler manuals.

[barnett468]

When I start out, I try to set the floats roughly parallel to the carb body and adjust from there if the above test doesn't put me where I need to be. If you adjust the float to put more pressure on the float needle to shut off the fuel flow, and observe no lowering of the fuel level, is the only conclusion to be drawn from that test that the float needle seat is worn out? Assume the carb was previously thoroughly cleaned out. Thanks.Some of the most likely causes of float bowl fuel levels that can not be altered/adjusted by adjusting the float height are:

Bad needle.

Bad needle seat.

Stuck float.

Sunken float.

[barnett468]

If you adjust the float to put more pressure on the float needle to shut off the fuel flow,...The purpose of adjusting the float is solely to set the fuel level. It is NOT to increase the amount of pressure it puts on the needle. As the the float goes past 90 degrees relative to the needle and seat, the force of the float on the needle actually becomes progressively less.

[webbch]

Different carb and engine combos use different settings. Some of the Kawi street bikes use a level similar to the green line.

I set the bikes like yours to the level I suggested on your other thread which is anywhere between the red and yellow line. Your red line is slightly high in the pic.

This is the level I have seen it come to when the floats are properly adjusted according to the factory spec which is measured in the actual float height.

This is also the method and spec I have seen in at least 1 of the 80's Yamaha 3 wheeler manuals.

When it has come to this level, do you happen to roughly recall the position of the float relative to the carb body? Is the float nearly parallel to the carb body (1)? angled slightly away from the carb body (2)? angled slightly toward the carb body (3)?

On the stock Keihin carb on my 200 that I simply COULD NOT get the fuel level correct, I tried all 3 positions of the float with 3 different float needles. The original position had the float angled toward the carb body slightly, which supports the concept of an overly rich mixture that I was fighting (if one assumes that parallel to the carb body ought to be pretty close to the right level). I was unable to ever get the fuel level below the green line in any of these 3 positions (didn't even try to start in these cases because I figured I needed to get the level adjusted to be between the red and yellow lines).

Due to these issues, I then installed a Chinese carb on my 200, and the fuel level test was right AT the red line...I noted that the float on this carb was perfectly parallel to the carb body. This carb is idling properly, and has just a slight hesitation at mid-range that I'm working on, so I suspect that I'm at least pretty close on the float level on this one.

Here's the one that skews my belief in the fuel level height....On the carb on my 185 (which is the carb in the pic) that WAS idling correctly (which I had NOT done the fuel level check previously), I did that fuel level check and noticed that the fuel level was closer to the green line. When I took it apart, the float was parallel to the carb body (being careful to hold the carb at an angle to ensure the float weight wasn't affecting the height). I adjusted the tab so the float was angled slightly away from the carb body, re-assembled, and then needed the choke to idle, suggesting I had leaned it out too much by that adjustment (pilot screw was already 2 turns out, which should've at least allowed it to run w/o choke). I'm inclined to think that I'm overly fixated on the fuel level height in these tests, and that, at least for this particular carb, the green level was an acceptable measurement, contrary to barnett468's experience, unless there's some other variable I'm overlooking. I thought the green level was reaching the overflow tube in the float bowl, but I may remove the float entirely and repeat the test to see if the level goes even above the green line.

[tri again]

Not much float info to add except I'd try the search key
to get every post ever written in one click o' da mouse.

I had one rebuild kit that had a Longer needle valve, guess
it was A way to lower the fuel level.
My other useless thought:
We always turn the gas off.
Consequently, it is not uncommon to get halfway back to the barn and have the engines die.
This is significant to me in the sense that they run GREAT until they die so my redneck engineering, survival thought is that the float valve, within reason, is to simply keep it from overflowing.
A low fuel level in the bowl means nothing until it runs out.

..and this is experience with 6 or 8 es / sx models.
Also does NOT mean it's right but works for us.

[MonroeMike]

I've always set mine according to the service data...no hose involved.

Pages 81-82.

http://www.3wheelerworld.com/showthread.php/126290-ATC185-200-Service-Data

[barnett468]

Here's the one that skews my belief in the fuel level height....On the carb on my 185 that WAS idling correctly, I did that fuel level check and noticed that the fuel level was closer to the green line. I adjusted the tab so the float was angled slightly away from the carb body, re-assembled, and then needed the choke to idle, suggesting I had leaned it out too much by that adjustment (pilot screw was already 2 turns out, which should've at least allowed it to run w/o choke).This is exactly what I meant on your other thread where I mentioned the following.

high float = richer

low float = leaner


Did it idle without the choke?

Did you try adjusting the fuel mix screw?

Since you needed to use the choke to start it after lowering the float, it makes perfect sense that it might not idle because as far as fuel regulation goes, both start and idle are controlled by the pilot jet.

If you would have put in a bigger pilot, it theoretically should have idled and less choke should have been required to start it.





at least for this particular carb, the green level was an acceptable measurement, contrary to barnett468's experience, unless there's some other variable I'm overlooking.Actually, this is not contrary to my experience or what I have said so you are simply misunderstanding something I said. Sorry if my comment regarding this was not clear.

There are several good articles online that describe carb function in detail. One place to start is by doing a search for "emulsion tubes". Below is a brief and partial explanation of their function.

An emulsion tube affects the fuel curve and also emulsifies air from the air corrector jet, with fuel. This "emulsification" process, induces air into to fuel which allows it to burn better. The tubes diameter, location [elevation], size, and number of the emulsion holes control its effect.




FLOAT LEVEL

I am certainly not the most knowledgeable person on carbs but I have tuned a lot of carbs and part of my experience with float levels is the following:

A level that is slightly higher than spec can have an adverse effect on idle. On a car it can also cause the car to die when decelerating quickly.

A level that is slightly low, has no noticeable effect on performance.

A level that is a lot lower than spec but still covering the jets on a motorcycle type carb, occasionally adversely affects the engines performance which can often be corrected sufficiently with proper jetting.

Due to these experiences, when setting float levels, I err on the side of caution and set them on the low side of the spec.

There is someone that did the plastic tube gas level test last week on a Honda, and he said his level was 1/4” below the red line you indicate and his bike started, idled and ran fine.




NEEDLE AND SEAT LEAKING –You mentioned that you thought your seat might be leaking because you tried 3 different needles and 3 different float level settings and the level was high and always the same.

If gas was seeping/leaking past your needle and seat, it would come out somewhere if you left the gas on. Since you did not say it was coming put the overflow tube, I would connect the gas line to the carb with the carb off, and see if it is leaking out the needle jet and idle circuit in the bore.
If it is not, then it seems to me that the needle and seat are not leaking in which case you have a strange problem for sure.





I'm inclined to think that I'm overly fixated on the fuel level height in these tests...

[barnett468]

Ok, in the link below, on page 4-4, you will see the gas level spec on a Yamaha YTM 200 3 wheeler with a 22 mm Mikuni along with a picture of the method I described for checking the gas level in the carb.


Here are part of the instructions letter for letter.

3. Install the carbulator to the machine. [How about "carburetor"]

6. Set the fuel cock the "ON" and start the engine. [Maybe "to the "ON" position."]

3.0 +/- 0.1 mm (0.12 +/- .04 in) [0.1 mm variance...really? That's only four thousands of an inch! How do you measure that, or is the .04 in measurement correct? lol.]


Their correct spec is almost 1/8" [3.0 mm] below your red line plus or minus .04" [not .004"].

http://www.oscarmayer.net/atc/manuals/Yamaha/ytm200_yamaha_servicemanual.pdf


PS - I see you finally got your 200 running good, congratulations.

[webbch]

NEEDLE AND SEAT LEAKING –You mentioned that you thought your seat might be leaking because you tried 3 different needles and 3 different float level settings and the level was high and always the same.


On the 200, I suspected of the problem you mention, but ONLY because I was trying to get the fuel level at or below the red line, which turns out to be a lost cause, due to a misunderstanding on my part. I now understand the problem all along with the original carb on my 200 is that the float level was WAY too high, causing an overly rich mixture, and is the likely reason I could not get it to idle, and why it was very slow to return from a rev. Unfortunately, I spent my time fixated on the fuel level test, trying to resolve a problem that wasn't a problem. At some point, I'll re-install the stock carb with a new float that is at the correct level, which should resolve the issues I was having with it. Right now, I have a Chinese carb on it.

Thanks for everyone's patience as I've struggled through my first several carb tuning experiences. I had the whole family out on the 3 trikes yesterday (110, 185s, 200s) now that they're all running decently and it was a lot of fun.

[barnett468]

Thanks for everyone's patience as I've struggled through my first several carb tuning experiences.

:w00t: Ok, cool, well you now know WAY more about carbs than a lot of people, including how NOT to adjust a float level. :)

[DohcBikes]

As Monroe Mike suggested, on a properly functioning carb, the manual specs and procedure will get you really close on the float level every time. Obviously different elevations, engine condition, and other factors will affect the optimal setting.

Get the spec, for example, I believe ~14mm for a 200, hold the floats at an angle in which the float needle just barely seats(~45° on many small carbs) and measure as specified. Adjust.