Float Height

How Well Do You Understand Why We Adjust Float Height?

  • I'm a Master.

    Votes: 2 50.0%

  • I Know Enough.

    Votes: 1 25.0%

  • I Know a Little.

    Votes: 0 0.0%

  • I Usually Need Help.

    Votes: 1 25.0%
  • Total voters
    4
Trfsrfr

Trfsrfr

I certainly have been getting a great education about carbs, jets, and float heights lately, but from what I have read here and on other forums it appears there are a good number of people that dont entirely understand the whys and hows of the float height setting.

I have a friend that told me that the float setting was only to ensure the jets stay submerged, and then I read an article that says that float height affects fuel pressure.

Could someone explain in-depth the ins and outs of float height adjustment, how it affects jetting, what effect altitude has, etc, or provide a link that explains it all clearly?

I read a lot of threads where the senior members just end up repeating themselves over and over and thought maybe we could help shed some light on this subject and help alleviate that issue.
Maybe make a sticky/pinned thread out of it?
 
SRAD97750

SRAD97750

Moderator
Staff member
The height of the fuel in the carburetor bowl, jet passages, and effectively the fuel's 'distance from the venturi' is determined by the float. The engine uses vacuum to pull the fuel and air into the cylinder through the jet passages and intake tract.

The closer the fuel is to the venturi or 'jet passage outlet' the easier it is for the engine's vacuum to pull the fuel into the venturi. If the float height is set higher, the mix will get richer because the vacuum can more easily pull fuel the shorter distance. Gravity plays a role in this distance and energy required to overcome it.

Another way to look at it is that the metering portion of the jet is at the intake point, the lowest point submerged in the fuel. So technically, the jet only 'meters' the replenishment of the jet passage. The actual quantity of fuel allowed to be set as 'static' in the passages, by the float, makes the circuit richer or leaner inherently. -BIG DAN:thumb:
 
Trfsrfr

Trfsrfr

And here I thought I was making a thread that would turn into a helpful, informative, go-to spot for solid tuning advice.
And what do we get?
Dick jokes.

I should have known!:doh:
:jacked::focus:
 
2strokesteve89

2strokesteve89

Trfsrfr:
And here I thought I was making a thread that would turn into a helpful, informative, go-to spot for solid tuning advice.
And what do we get?
Dick jokes.

I should have known!:doh:
:jacked::focus:
Click to expand...

You'll get more posts with good technical input. DAN was pretty much spot on with his description of how the float level affects all of the circuits in a carburetor, the only thing I would add is many times the possibility of a sunken float is overlooked when going thru a carb, so if you set the float level but the float doesn't float you'll end up withoverfueling problems as well.......and by the way, when I see an oppurtunity for a good dick joke I don't pass it up.
 
PALMER84ONE

PALMER84ONE

2strokesteve89:
You'll get more posts with good technical input. DAN was pretty much spot on with his description of how the float level affects all of the circuits in a carburetor, the only thing I would add is many times the possibility of a sunken float is overlooked when going thru a carb, so if you set the float level but the float doesn't float you'll end up withoverfueling problems as well.......and by the way, when I see an oppurtunity for a good dick joke I don't pass it up.
Click to expand...

:lol:
Trfsrfr:
And here I thought I was making a thread that would turn into a helpful, informative, go-to spot for solid tuning advice.
And what do we get?
Dick jokes.

I should have known!:doh:
:jacked::focus:
Click to expand...

Like Steve said, when opportunity arises.. :D
 
Trfsrfr

Trfsrfr

A question occurred to me as I was thinking about floats;
If the mixture is richened by a higher float, can that be offset by using smaller jets, and the same for the opposite?
And if so, is there any advantages or disadvantages or trade-offs of this? A mixture going lean because of rough terrain comes to mind for a low float setting...

Right now the float height on my YZ is set at 6.5mm, right in the middle of the range (5.5 - 7.5).
The dark plug pic I posted in that thread was with a 172 jet. When I put in the 178 jet it didn't get better.
The plug didn't get better until I put in the 170 jet.
So then isn't the 5.5 to 7.5 range just a "neutral" area for which one can jet accordingly? If so, that wouldn't that explain the discrepancy between some of the members' differing opinions on what size jets I should be using?

I have also heard some talk of people having a "wrong" float setting and jetting to "correct" that, but if it's anywhere in the float range given, wouldn't that be the preferred way to do things?

Example: if a guy sets his YZ float to 5.5mm and uses a 180 main jet and gets a nice color plug, wouldn't that be approximately the same as a guy setting his float at 7.5mm and using a 168 main jet to get the same color plug?

Just thinking out loud here trying to get a better understanding of this stuff.
 
Last edited:
PALMER84ONE

PALMER84ONE

I never do plug chops and look at how it's colored. Although you can determine if you are lean, rich, or right on it has never been an issue, plugs don't foul, bike runs crisp enough for a hack like me. If the bike starts easy, runs strong through all gears and throttle ranges, its good to ride. I have been doing so looking into the PMW carb that came on the 01 250 and many say it's junk and finiky. In other words it was, throw the PWM away and get a PKW, $265.00, and you're jetting-float level problems will be done.

And to answer your questions, comments, above... No, I don't believe it to work that way.
 
P

PawPaw

Attempting to re-jet to cure a float height issue is like using a sledge hammer to drive a finishing nail.
Set the float height correctly and then jet.

Paw Paw
 
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