Randall Washington, aka "Randakk"
President and Chief Executive Rider
Chapel Hill, NC USA
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Return to main Tech Tips Index Floats 101You might consider this item. I show how to set floats in the video: Randakk's GL1000 Carb Rebuild Video Note: The procedure for setting the float levels on GL1100 carbs is essentially the same as the one for GL1000 carbs described below. The only difference is that the float level spec for the GL1100 is 15.5 mm instead of 21.0 mm. Setting floats on a GL1000 is relatively easy. It is a critical step in any carb overhaul. Problems with float operation affect all aspects of a bike's performance and "drivability." Unfortunately, the available manuals have weak descriptions of this procedure and the accompanying photos are rather poor. Worse, there is some printed material and web sites which are FLAT WRONG in the advice they give on setting floats on a GL1000. Here's how I setup floats. My method is time-tested and bulletproof. Properly adjusted floats will stay in calibration for a very long time. Float Theory Floats are necessary on carbureted engine to regulate and control the precise level of fuel in the fuel bowl. This must be done in the context of widely variable fuel usage rates.
On a GL1000 the fuel flow to the carbs from the fuel tank is handled by a mechanical fuel pump that delivers fuel at about 2 psi regardless of demand. In low demand situations (e.g., idling), excess fuel delivery by the fuel pump must be diverted to prevent flooding. Flooding in a GL1000 is serious because there are no external bowl overflow circuits. If a GL1000 carb floods, it can dump large quantities of fuel directly into that cylinder. This can lead to a minor problem (hard starting, stalling, etc.) or catastrophic engine failure (hydro-lock which can cause bent rods!). Fuel regulation is accomplished by the rise and fall of each float. As the float rises to the appropriate level, the float pushes against a rubber-tipped float "needle" which operates against a precision machined "seat" to stop the flow of fuel. Likewise, when the float falls, the float needle opens the fuel inlet and allows fuel to flow into the bowl. In actual operation, the float needle oscillates through a relatively small range of motion. Sometimes theorists describe this motion as "vibration." A running engine has a constant need for fuel, so the float needle is rarely 100% closed. Rather, it's mostly regulating the flow rate of fuel into the carb bowl. Only when the engine is shut down, does 100% closure need to occur. To protect against the possibility of float valve failure when parked, always use the petcock to shut off the flow of fuel every time you shut off the engine...that's why it's there. Yes, I'm well aware that the fuel tank is below the seat on GL1000s and that a mechanical fuel pump is necessary on these bikes to feed the carbs. However, the fuel pump can come to rest in a certain mode that allows fuel to flow when the tank is full or near full. At lower tank levels, siphon action can do the same! The float needle has a spring loaded tip to allow a positive fuel seal while protecting the seal tip from too much pressure and vibration wear. Sequence of Events The recommended general order of carb re-assembly:
This sequence is important because it protects the delicate stuff on the bottom of the carbs...like the precise setting of your floats! Float Alignment / Prep Prior to setting the float height, you should check each float carefully to make sure that it is square, plumb and that the pivot is true. I use a precision right angle device and lots of visual inspection. Adjust each float as necessary. This is a critical step. Unless the geometry of each float is identical, you won't get consistent mixtures across all 4 cylinders. Poorly aligned floats can "foul" on adjacent structures and cause chronic fuel starvation or flooding. I take an additional step...I weigh all four floats to make sure they are evenly matched. On my scale, clean floats weigh 12 grams. I throw out any outliers than vary by more than 1 gram. The synthetic floats used on GL1000s aren't prone to saturation like old-fashioned brass floats, but weight-matching is a good idea nonetheless. Below are some pictures which show pairs of floats. The float on the left in each pair is a perfectly aligned float. Each of the floats on the right has an alignment problem. The problems have been exaggerated for clarity. When you finish this inspection / alignment, your float should be square (parallel or perpendicular) in every plane relative to the carb body. Be very careful when bending your floats into alignment. They are rather fragile and are easily damaged.
Also, you should clean and ream the float pivot holes (on the float). Don't remove excess amounts of metal or you will corrupt the geometry of the float pivot-to-float pin relationship. Likewise, verify that there is no binding on the float pivot pins where they insert into the posts in the carb body. Polish the pins with crocus cloth and ream the posts as necessary to get a snug but free fit. When correct, you should be able to insert the float pivot pins with fingertip pressure only. Again, don't remove excess amounts of metal. Float Setting The correct spec is 21 mm. This is measured from the bottom edge of the float to the raised lip adjacent to the carb body fuel bowl gasket surface. Important point of clarification: "bottom" edge is defined as oriented when installed on the bike. Remember this fact when your carbs are upside-down or tilted up on their end on your bench. When you take your measurement, be sure the spring loaded "tip" of the float valve is contacted but not depressed. The best way to accomplish this is to set the rack up (on end) on your bench and tilt it slightly away from vertical so that it rests against something sturdy (I use my bench vise). Then measure the floats on the lower pair of carbs. Important - the float you are measuring must be hanging from its float pivot pin. Here's how I place the carbs on my bench to measure and set floats. Notice the two rubber furniture coasters I use to keep the rack steady:
Some manuals repeat the generic advice to measure "from the gasket surface." This is vague and misleading in the case of the GL1000. Here are two pictures showing where and how to measure GL1000 floats. Notice that the gasket is in place for these photos! Notice also that my float gauge is clearly resting on the raised lip rather than the gasket surface. Measuring from the gasket surface will produce float settings that are too high and result in an over-rich condition! Correctly set floats will be parallel to the main carb body flange along the entire length of the float edge. I have a variety of shop-grade precision tools which I can use to measure and set float heights. Each of the measuring tools below is set to measure 21 mm. I usually reach for the 69 cent item shown in the picture below sourced from Ace Hardware. You don't need anything fancier to get excellent results. Be sure to measure both sides of the float!
The adjustment should be done at the "tang" that contacts the float needle. You will see some instruction elsewhere and in some manuals advising that you adjust float level by bending the float arms...NOT!!! My view is that bending the 2 arms of the float instead of the single tang is lunacy. Bending the arms introduces all sorts of unnecessary geometric distortion of the float. Accepted practice for generations across dozens and dozens of carb manufacturers has always been to adjust float level at the "tang." My theory is that this "arm bending" idea crept into the picture from some sloppy translation and technical writing work from the original Japanese text. Believe me, the engineers at Keihin intended for the float height adjustment to be made at the tang. Here's a photo below showing the "tang" where the float height adjustment is made.
Adjust the "tang" as necessary to get the measurement to exactly 21 mm. Also, when the measurement is correctly set, the bottom edge of the float should be exactly parallel to the carb body along the entire length of the float…not just at one point of measurement. When satisfied with the first pair, flip the carbs over and repeat for the other two. Note: In addition to the above details, correctly set floats should have a "gap" of about 2 mm under the float "tang" relative to the surrounding float arm architecture. I can usually take this fact and eyeball float levels to within 1 mm of perfect before I even begin to measure. Caution: There is also another tab on the float which limits downward movement. This "down stop" tab rarely requires adjustment. Unfortunately, sometimes folks get confused and think this is the "tang" where you adjust to set float height. Unbelievably, I recently had a professional motorcycle mechanic correspond with me about problems he was having setting float height on a GL1000. Turns out he was trying to make the float height adjustment at the "down stop" tab. It's purpose if to prevent the float from "fouling" when in the fully down position. If you mess with these, its possible that the floats might not be able to "drop" to allow fuel to enter the bowl. In fact, this can result in a high speed fuel starvation and over-lean condition. In extreme cases, this can cause your bike to overheat to the point that the exhaust manifolds will turn cherry red! Properly adjusted down stop tabs will permit the float's forward edge to drop about 1/4" from the fully up position (as installed on the bike). This should coincide with the bottom edge of the float dropping to a parallel position with the bottom of the main jet towers when the float is in the full "down" position. (Remember, if your carbs are upside-down on your bench the direction of movement direction is reversed). Adjustment of the down stop tab is not nearly so critical as float height. So long as the down stop tab will permit the float to drop when the fuel level drops and stops the float before it contacts the bottom of the float bowl, you will be fine. Below is a picture of the Down Stop Tab. This is NOT used to set float height!
FINAL CAUTION: Make sure the float needle clip doesn't bottom out and contact the float seat. This can happen on some aftermarket float sets because the needles are not long enough or the seats are too deep. In my own work, I always use OEM Honda float sets to avoid the disappointing quality issues with aftermarket float needle sets. Note: The procedure for setting the float levels on GL1100 carbs is essentially the same as the one for GL1000 carbs described above. The only difference is that the float level spec for the GL1100 is 15.5 mm instead of 21.0 mm. Return to main Tech Tips Index Intellectual Property Notice: All material appearing in this website is the property of Randall Washington, and is protected under United States and international copyright laws. The photographs, text and other content may not be copied, reproduced, distributed, stored, or manipulated in any manner without the express written permission of Randall Washington. For more information on the use of material from this website, click here |
