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Carburetor Float Balancing Print E-mail

Setting the Carburator Float Height

Introduction:

Setting float height is a basic adjustment in carburetor maintenance and while basic in nature, performing the operation correctly and more important, consistently can make the difference between a poor performing machine and a highly tuned performer.

 

Components:

The necessary components to set float height are:

Easy access point on the float (generally a flat that can be consistently observed without parallax) Reference point usually on the carburetor body (this point needs to also be flat and easily observed At the same time as the float reference point. Needle springs (should be free moving - preferably new) sticking needles can throw off float height)

Adjustment tang (on float body - this tab pushes against the fuel inlet needle forcing it closed)

Tools:

  • Adjustment measurement tool (linear measurement)
  • Calipers
  • Depth gage
  • Steel machinists rule (this is basic - about $1 at most supplier stores and accurate to 1/64" or 0.015")

GOAL:

Accurate and sufficient fuel level in the float bowl

  • Too low fuel and the bowl may run dry under full throttle
  • Too high and carburetors may leak fuel through overflo under conditions of sudden flow change.

The main thing to remember is consistency. Changes in fuel level in the float bowl will cause the overall carburetor mixture to change either leaner or richer than. The original, correct mixture settings.

Process:

Float height is generally set by turning the carburetors upside down and removing the float bowls. Most tuning manuals will indicate (some better than others) where the measurement points are on Both the float itself and the carburetor body along with the recommended measurement.

NOTE: Often the recommended measurement points are ambiguous, difficult to use or difficult to get consistent readings from. Consistency is the key to good PERFORMANCE.

Pick your spot where you feel you can get the best readings on the carburetor base. Using your measuring device, find a spot on the float that you feel will allow you to make easy, reproducable results.

Using the manual defined measurement points check your float height and record it. Now using your points and method, measure again and record this value. Do not change height yet. If your machine is running well and your plugs look good leave the where it is right now. If your machine is not running well, then you have nothing to lose. Using the manual's prescribed points, measure your float height and set to the specs supplied. Now using your selected measurement points and method, measure the float height again. Record this value. This is your spec float height.

So How High is the Fuel?

Ken Talbot of the XS11 Owners Association has come up with a setup for the sighting of the fuel level in your carbs. His method is described below including pix.

In the past, I have always just set my floats with a micrometer. This ensures they all look the same, but it doesn't tell you what the fuel level actually is in the float bowls. They could all be high or low, or you could have one or more off if your floats are a bit off in weight. The manuals talk about getting the bike perfectly level, then checking the fuel level with a clear tube attached to the bleeder on the bottom of each bowl. The trouble is, if something is off, you have to remove the carbs to do any adjusting, put the carbs back on, and hope you've got it right. This is why I have never used the clear tube method. I can peel off a bank of carbs and reinstall them a lot quicker now than the first time I tried it, but I still wouldn't call it fun.

That is, until today. How's this for a bit of bush league carpentry to make this job a whole lot easier?

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The tank cost me five bucks at a lawnmower repair shop. The rest was scraps I had laying around. Here's a view with the carbs sitting behind the main apparatus.

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The board going left to right holds the bank-o-carbs level side to side. The rear piece holds them level front to back. One of the benefits of this rig is you have real easy access to the bleeder screws and it is easy to get the tub up against a float bowl for checking.

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If you have to reset a float, it is easy to tip them back over to drain the gas, pull off one float bowl, perform the adjustment, put it back together, and retest the level. And finally, an action shot....

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 Conclusion:

The irony of the situation with setting the float height on carburetors to me has always been that the goal is to set the fuel height inside the float bowl during operation consistently at a specfic height yet the actual configuration and measurement is made without fuel in the bowl with the carbs upside down!

Remember there is no wrong way to do this measurement and calibration. The goal must always be consistency, consistency, CONSISTENCY! Float height affects ALL carburetion circuit mixtures and therefore can throw your whole carburetor off if it changes during operation.

Rick Jemison & Ken Talbot

More Carburator Float Adjustment

I'd like to add a suggestion to Ken's fine work.

If you have an old set of used rubber manifolds you can mount them to a board at the correct distance apart and use that to hold your carbs while toying with the float levels.

The idea is to mount this board to another board 'foot' and use some sort of bubble level to make sure the carbs are level. Then mount a tank much like Ken describes to get gas to the carbs.

There is a drawback to either of these schemes in that the manual states that after making an adjustment to the float level, you should run the engine for 5 minutes to make sure the float has found it's normal level with the new adjustment. I don't know if this is a real world suggestion on the manuals part or some sort of hoop that the Yamaha writers thought folks ought to jump through. Your guess is as good as mine.

Mike Saar
 

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