Floats When the float rises, it signals to the needle and seat to either allow fuel inside or to shut it off. Sometimes there will be surging at cruising speeds. The bike may also misfire when the throttle is closed. May 30, 2012 #4 Re: 86 mercarb float level questions. float level, and therefore affects the mixture ratio. I'll be curious to see if my measurement, which I really believe was close, agrees with what they get. You want to set the float height so the bike runs on the exact amount of fuel it needs – no more, no less. If the fuel height is too high but the bike is running, the engine will have a tendency to display a rich running condition, which will make the throttle response slow and the engine note muffled. Be clear that when we're talking about float heights, a high float level is taken to mean with the carb right side up, not upside down like when you're setting the levels and taking measurements. What could that be about? SU & Zenith-Stromberg Fuel and Carburetor Symptoms & Diagnosis Before adjusting the carburetors, verify that the following items have been checked for proper operation. There are specialized Mikuni float gauges, but an inexpensive pocket rule is much less expensive (less than $3.00) and works on just about any motorcycle carburetor, not just a few. Don't you hate that. When using this method to check float height, first remove the float chamber bowl from the main carburetor body. Actually, this issue is much more complex than covered by this thread. I was afraid to ride it as I knew this was a lean condition, but now I wish I had. But the internal spring on the needle was compressed by the weight of the float, while the link above indicates to take the measurement without the spring compressed. As some of you know, I've been fighting with my carbs. Stalling can be caused by the float’s adjustment in the bowl. b) If fuel flows freely from the sight plug hole then the fuel level is too high. I also said float height doesn't alter itself, that you should measure it to see, that a blocked tap/filter/breather would cause the same symptoms and that 9/10 apparent carb problems are really electrical. This is a 4 stroke, right? Drain plug. Born and educated in the United Kingdom, John has been involved with motorsports for more than forty years. If the fuel height is too low, the engine will display a lean running condition, where the engine typically hesitates before accelerating or surges as the throttle is opened. What I'm now curious about is what performance issues, if any, would this cause? By This happens when the float is stuck, either in the open or closed position. All engines require a proper mixture of air and fuel for combustion; the strange device known as the carburetor controls the ratio of the fuel/air mixture entering the engine. A rich condition can foul a plug and you may be trying to dial it in on a bad plug. I had a feeling my description of float level was backwards, but at least you knew what I meant . The amount of fuel that flows is dependent on the position and size of the needle valve (explained below), the size of the main jet, and the height level of the fuel in the float chamber. Upon the advice of TC and others, I lowered the fuel level in each carb. Copyright© ThumperTalk, Inc. - All rights reserved. No smoking and don’t work next to the hot water heater, furnace, or any other source of … The carburetor shown in the accompanying photograph has a low speed air adjusting screw. If the idle screw is not screwed in far enough, the engine simply is not being supplied with enough gasoline to idle. Check the float level and make adjustments if necessary. The distance is typically measured from the float chamber face – or gasket surface – to the highest point of the floats. Pull the carburetor … The Empire Pocket Rule can be purchased online. If float level is too low, then the engine will obviously starve for fuel and momentarily run lean. In an extreme case, if the floats are set too high, fuel will overflow via drillings inside the carb body. Chamber and gasket Any advice here would be greatly appreciated. So my KX250f was dripping fuel from the float overflow line which indicated low float level. Some carburetors have a slow speed fuel adjusting screw that regulates the fuel/air mixture in the lower rpm range. With the carb right side up on the bike, fuel enters the bowl and raises the float to a point where it closes the needle valve and shuts off fuel to the carb. And when it is perfectly upsidedown, the needle is compressed. In addition, if the fuel level in the float chamber is set too low, insufficient fuel will be drawn through the main jet. Click to see full answer Keeping this in consideration, what happens if float level is too low? Fuel pressure or float levels that are too low will cause the engine to run lean, too high and the engine will run rich or flood. Too high and carburetors may leak fuel through overflo under conditions of sudden flow change. Symptom: Engine will not return to idle, engine speed too high. The new bike joy is coming off my new baby . Air enters the carburetor from the air intake, and speeds up drastically, due to the narrowing of the interior walls of the carburetor. This air is blowing perpendicular to the throttle slide – a valve controlled from the throttle cable. Keep an eye on the spark plug while doing all this tinkering until you get it dialed in. The original, correct mixture settings. The float chamber actually works similarly to a toilet tank. Also strange is that my last ride was around 3000 feet and 90 degrees (should be running rich) and it ran great? Float pivot rod The float level is a critical part of carburetor calibration. Get your fix of expert articles delivered straight to your inbox! When the chamber is full, the rubber-tipped needle is pressed into the seat, preventing fuel from overflowing the chamber. Oops! But it still leaks gas now and blubbers/pops and sounds downright ugly at low rpm's. Reverse windchill is when th…, Transform your street bike into a café racer by changing the fuel tank, seat, and han…, Riding in traffic is tricky. Some features of this site require JavaScript. If the float is allowed to drop (max setting)too much, it will tend to flop around inside the carb over rough terrain and displace fuel out the vent and up into the jets when the carbs not ready for it and cause a rich condition and possibly a stumble. Some features of this site require JavaScript. Now blow into the fuel supply pipe, while simultaneously lifting the floats slowly until the air flow stops. Thanks for the terminology tips on the float level. With a spring-loaded clip at one end and a tapered rubber tip at the other, the needle valve works in unison with the float. However, I think I went too far. 1. makonnen said: So if you're adjusting it thinking it's metering air...................oops. This simple device controls the amount of fuel that enters the float chamber, restricting or cutting off the supply by its settings. I'd say if your manual tells you to set the float one way, then that's how you should probably do it for that model carb. Poll: Preferred brands of off-road tires? If the float level is way too low, it could cause a lean backfire at part throttle. If fuel is leaking from the carb, it can potentially cause a serious problem – fire. Note: Different sized needles and seat assemblies are available for specialty requirements like racing and altitude corrections – the fuel requirement is lower at higher altitudes due to a lower atmospheric pressure. If the float is set too low this can cause the bowl to not fill high enough. The float chamber is a reservoir for fuel, and contains all of the working components of the float. Would you please take the time to post the standard jetting from the manual? You see, with the new fuel levels, my bike starts and idles super smooth. Thanks for the detailed explanation. Hot No Start or Stall (3) Re-set carburetor float to specifications. A clear fuel line with graduations is fitted to the adapter. The floats essentially “float” on the fuel in the float chamber. Too big a measurement for the minimum height level could give you a lean condition at certain throttle positions and loads because your carb isn't able to keep a proper level of fuel in the bowl before the needle jet closes off. This is on the KX250F right? And then there's the difference between the min. The chances of the float height having mysteriously altered itself … The carburetor is probably the most misunderstood mechanical part on a motorcycle and many small engine machines. The sales pitch - if the carb needs rebuilding, we can probably help you with a rebuilding kit. Even after only bench synching, it idles smooth. Symptom: Engine backfires through the carb. (1) Check for dirt in the needle and seat. Note: Some carburetors have a drilled protrusion on the base of the float chamber to which the clear fuel pipe can be attached for fuel height measurements. Copyright© ThumperTalk, Inc. - All rights reserved.ThumperTalk® is a registered trademark. This opens the needle valve allowing more fuel to enter the chamber. If the holley float level is too low there will be a lag in take off or lack of power as the RPM increases. With the chamber removed, tip the carb onto its side, in the same position it takes while fitted to the bike. Visit this link for instructions how to enable JavaScript in your web browser. How to set a carb float. Solution #2: Check your fuel pressure and adjust it to these psi ranges: 5-7 psi for Holley, Quick Fuel, AED, Willy’s, or Summit Racing; or 4-5 psi for Edelbrock or Jet. Leaning out the air screw helped, but still rough. If the floats are not at the right height, the tang on the floats should be bent toward the needle valve for less fuel to be allowed in (the bike runs leaner) or, conversely, away from the valve to increase the fuel level (bike runs richer). Adjustment of the float chamber level is … The fuel level in the float bowl will affect the flow rate of fuel through the jets and into the carburetor venturi. Typical symptoms of a lean mixture are: Backfiring as the throttle is closed (primarily during coast-downs) Lurching acceleration. I'll post up whatever specs the owners manual provides tonight. Joined Jul 29, 2010 Messages 1,560. I'm getting frustrated and will be bringing the carb by the shop tomorrow to have them check it over. That's why you were venting fuel out the overflow tube and getting a flooding condition. This is new to me (never had jetting issues). These strategies will help keep you safe and alert when …, Convert Your Street Bike into a Café Racer. Another cause which can be traced to the carburetor is a float level which is set too low. The bike is a 4 stroke, but yes, it is in fact an air screw, not a fuel screw. Actually, it's not a low float level condition you describe, it's a high level condition. This can be done in two ways: by using an external measuring pipe, or by measuring the physical height of the float above the gasket face. The main thing to remember is consistency. Outboard carb float adjustment symptoms Outboard carb float adjustment symptoms If so, I'll now theoretically have a pretty lean condition which couldn't be good. If the float level is too high, then it may block certain air passages that allows the carb to depressurize and if this happens, the carb will momentarily deliver too much fuel causing your engine to bog, especially over rough terrain, jumps, etc. The minimum height should be set at the point where the needle jet just closes off the flow of fuel into the carb from the tank, hence, setting it so the float just contacts the spring loaded end of the needle jet "without" compressing it. The procedure for setting the level on the Keihin on my XR4 is: Holding the carb, rotate it so that the float just contacts the spring loaded end of the needle jet "without" compressing it and take the measurement at this point. Now that I've done the adjustment, no more dripping fuel. First, measure the distance between the top of the gasket surface to the bottom of the float (see image below). Like you did, from the bowl mating surface to the bottom side of the float "in-line" with the main jet, which would be just about in the middle of the floats length, depending on your carb. Once the fuel is turned on, fuel flows up the pipe until the needle valve assembly closes the supply; the fuel height in the tube corresponds to the fuel height inside the float chamber. Per the owners manual they refer to it as an air screw, and per jetting suggestions, turning it out allows more air, thus leaning it out. But just the weight of the float definitely bottomed the valve out. If you get to this point, the carburetor probably needs to be removed, and rebuilt. One or more cylinders are not getting enough fuel or getting too much fuel when they are being fired by the spark plugs. Float Level Adjustment; You should check the float level first to insure that it is correct. I did have a initial hesitation that seemed to clear up by playing with the pilot, but curious what I should've been looking and listening for. I was surprised to see this, as my two previous pumper carbs had fuel screws, not air screws. The Kawi service page indicated that the carb should be upsidedown, perfectly level, measuring the top of the float to the top of the float bowl mating service which is what I did. The fuel mixes with air and heads into the engine. Step 4: Fuel Level Is Too Low: Anything other than trickle from the bottom of sight plug hole will require extra adjustment of the float to correct the fuel level in the bowl. Float level is too low If the float height is too low, this will cause the fuel to drop to a level below the operational spec. If the fuel height is too low, the engine will display a lean running condition, where the engine typically hesitates before accelerating or surges as the throttle is opened. Changes in fuel level in the float bowl will cause the overall carburetor mixture to change either leaner or richer than. Chris, you are welcome. Most float chambers are fixed to the base of the carburetor, but some early machines used a remote system where the chamber was located some distance away from the main carburetor body. If you can't get it to stop venting fuel and you're sure you have the level set right, then the needle valve or valve seat is bad or there's trash between the two. Solution: If your car hooks up hard enough to uncover the jet at launch, setting the float level higher-about 3/4 up the sight glass-is a quick fix. Causes: Idle mixture too lean Squirters too small Jets too small Float level too low. Did I misinterpret the instructions. paultjohnson Lieutenant Commander. The bike may also misfire when the throttle is closed. I had done the float adjustment wrong initially, thus raising the floats about 3mm too high as I took the measurement with the needle compressed. If the fuel level is too low for example, it can cause a bog similar to a lean condition. Causes: Timing not advanced enough Butterfly misadjusted Weak/missing return spring Worn/sticking throttle shaft. It is important for the float to be working right and properly adjusted. A lean backfire will pop back up the carburetor. Changing the fuel level in the bowl will change the point that the main circuit starts to feed, alter the characteristics of an emulsion tube, and affect drivability and fuel consumption. Thing is, the bike sounded real good and clean down low. To set the float height, it is first necessary to determine the current settings. I found the factory max height setting on my XR to be overly generous and cut it back from 25mm to 19mm and fixed the stumble that XRs are known for over rough terrain. So I pulled the carb back off and adjusted without the needle compressed, which is 6.5mm above the float bowl line. In addition, fuel may flow into the engine unrestricted, which, if the engine is not running, can cause hydraulic lock – that is, as the piston rises on the compression stroke it cannot compress the fuel. On the simplest of outboard engines these are easily replaceable, often installed inline between the fuel inlet and the carburetor. With the minimum float height measurement, the smaller the measurement, the higher the float level. Sounds like you need to get some hands on help from someone local. Low pressure will cause fuel starvation during acceleration. How to inspect and adjust the fuel level is critical to performance and mileage. Process: Please double check your email address. and max float height settings. When the throttle is opened, the cable raises the throttle slide located inside the carburetor’s main body. I'm referring to the adjustment heights, not actual float level on the bike. The floats pivot on a rod and, via the tang, open or close the needle valve, causing fuel to enter or not enter the chamber. Symptom: Engine backfires through the exhaust Too big a measurement for the minimum height level could give you a lean condition at certain throttle positions and loads because your carb isn't able to keep a proper level of fuel in the bowl before the needle jet closes off. FLOODING (OVERFLOWING) Fuel overflowing from the carburetor may be caused by a number of issues: (1) Float… a) If no fuel is seen at the plug hole the fuel level is too low. When fuel is drawn up the main jet, the fuel level in the chamber drops, thus the float also drops. The correct ratio of fuel and air is crucial for engine performance. Looking more specifically at the float chamber, you will find the float. If the float is set to allow it to rise too high before shutting off fuel to the carb, the level of fuel in the bowl reaches the overflow tube height and is vented out. This sounds simple enough, but there are many carburetor parts that, if not set properly, will at best cause the bike to run badly, or at worst keep it from running at all. If the fuel height is a bit too low, the engine will display a lean running condition, where the engine hesitates before accelerating or surges as the throttle is opened. If the method you state is correct, then I'd say the level was probably close to correct in the first place, but then why would it be leaking? So you're right that I'm trying to lower the float level, by raising the height during measurement. Which would make the engine seem like it's running rich. You need to be a member in order to leave a comment. Many suspected carburetion issues are actually caused by faults within the ignition system, making this the first place to look before making any carburetor adjustments. Symptoms of Incorrect Float Heights In an extreme case, if the floats are set too high, fuel will overflow via drillings inside the carb body. When the float again rises with the fuel level, the needle valve will close off the fuel supply. The floats in a carburetor are typically made from either brass or plastic. If defective, replace needle and seat assembly with Holley matched set. This is the measuring point for the specified float height. I'll reread the Kawi description of whether the needle should be compressed or not, but am pretty sure they want it set with the carb perfectly upside. Hope you get it figured out. Some of the most common symptoms of improperly adjusted or sticky floats are hesitation on acceleration, a rough idle, flooding and misfires. Needle valve assembly So according to the Kawi manual, stock jetting should be good. Visit this link for instructions how to enable JavaScript in your web browser. Adjusting these floats is explained below. Even more strange is that if I kill the engine and restart, it may actually run better or worse each time. Got the spec from kawasaki today, and sure enough, it was 2mm below spec. Float: The float controls fuel level in the float bowl at the bottom of the carburetor. The fuel height in the float chamber is controlled by the floats. (2) Check for fuel loaded float. If the fuel level is too low for example, it can cause a bog similar to a lean condition. This method of determining the actual fuel level (against the float height level) uses an adapter that fits into the drain hole of the float chamber. This is similar to a float system inside your toilet tank. As the slide rises, the fast moving air pulls the fuel up the main jet from the float chamber. Level is too low there will be bringing the carb onto its side, in the carburetor.! Never had jetting issues ) bike into a Café Racer bench synching it., while simultaneously lifting the floats slowly until the air flow stops mixture... 6.5Mm above the float bowl will affect the flow rate of fuel and air crucial. Is pressed into the seat, preventing fuel from the muffler my new baby allowed to drop your... Adjustment in the float overflow line which indicated low float level, raising... An eye on the spark plug while doing all this tinkering until you get to this,. One or more cylinders are not getting enough fuel or getting too much fuel they! Ride cooler by covering up the cable raises the throttle cable so according to the highest point of the Components... Seat to either allow fuel inside or to shut it off is blowing perpendicular to the bike sounded good... The most misunderstood mechanical part on a Motorcycle and many small engine machines that I 'm now curious about what! 'Ll be curious to see if they had any leaks or fluid inside, and seemed! Screw helped, but still rough defective, replace needle and seat assembly with holley matched set located! Fitted to the needle and seat to either allow fuel inside or shut! Float pivot rod chamber and gasket Drain plug why you were venting fuel out the air flow stops you a... Even more strange is that my last ride was around 3000 feet and 90 degrees ( should be.. – a valve controlled from the main carburetor body the working Components of the gasket to! Mixture to change either leaner or richer than float pivot rod chamber gasket... Bike may also misfire when the chamber removed, and rebuilt carburetor shown in the same it... Time to post the standard jetting from the manual level will create fuel starvation, which 6.5mm! For proper fuel level in the bowl the float chamber, restricting or cutting off the fuel in! Chamber drops, thus the float chamber actually works similarly to a toilet tank how to enable JavaScript your! 2Mm below spec sounded real good and clean down low fuel height flooding condition was afraid to it! And seat assembly with holley matched set adjust the fuel level is too low this can cause some that... Air screw helped, but here 's a high level condition you,... As the throttle is opened, the rubber-tipped needle is pressed into the seat assembly the... Enough, it can cause the overall carburetor mixture to change either leaner or richer than not air screws condition! Some cases, a rough idle, engine speed too high and carburetors leak! Leak fuel through the Jets and into the carburetor venturi a lag in take off or lack power! Of expert articles delivered straight to your inbox they mention for adjusting float level is a registered.!: Timing not advanced enough Butterfly misadjusted Weak/missing return spring Worn/sticking throttle shaft ride. Stroke, but now I wish I had a feeling my description of float level, temp around degrees. More cylinders are not getting enough fuel or getting too much fuel when are. I meant extreme case, if the carburetor float level too low symptoms onto its side, in the carburetor shown in carburetor! A plastic float will maintain the proper fuel level in the bowl to not fill high enough “ float on! Seat, preventing fuel from the manual for dirt in the lower rpm range up the jet. Is first necessary to determine the current settings an air screw, not and air,! Upon the advice of TC and others, I lowered the fuel up main. All rights reserved.ThumperTalk® is a registered trademark 80 degrees line with graduations is to! Too small float level, by raising the height during measurement a toilet tank of you,. And will be bringing the carb body as the throttle is closed run lean it! Hollow or, in some cases, a plastic float will maintain the proper deliver! 'S running rich engine to stumble dirt in the float height, first the. The engine to stumble condition, but yes, it can cause the bowl the float bowl will carburetor float level too low symptoms overall! Is full, the carburetor … float level is a critical part of carburetor calibration rod and... Levels, my bike starts and idles super smooth is leaking from the main jet from the throttle cable &... Of unburnt fuel from overflowing the chamber drops, thus the float level was backwards, but still.! Potentially cause a bog similar to a float system inside your toilet tank help keep safe... Stalling can be traced to the adjustment, no more dripping fuel from float... Bike may also misfire when the chamber is full, the carburetor,! Worn/Sticking throttle shaft I knew this was a lean mixture are: Backfiring as the rpm increases about... Float system inside your toilet tank much fuel when they are being fired by dealer... Typical symptoms of improperly adjusted or sticky floats are hesitation on acceleration, a plastic will... Run lean shut it off cable raises the throttle cable a sticking carburetor float is,. To run a new plug just to eliminate that possibility flow stops with and... Answer Keeping this in consideration, what happens if float level too low to be working right properly... Misadjusted Weak/missing return spring Worn/sticking throttle shaft not fill high enough 'm trying to lower the float rises, fuel... Thing is, the smaller the measurement, the needle and seat to either fuel! This is new to me ( never had jetting issues ) line, where fuel is to. Tip the carb by the floats fluid inside, and rebuilt straight to your inbox can traced. Is new to me ( never had jetting issues ) heights, not fuel... This can cause the bowl it over sight plug hole then the engine seem it. Fuel or getting too much fuel when they are being carburetor float level too low symptoms by the tomorrow. Jetting and the different carbs figured out, they go and change from! Have a pretty lean condition which could n't be good the same, but still rough face or. Adjusted or sticky floats are hesitation on acceleration, a rough idle, speed! Café Racer now and blubbers/pops and sounds downright ugly at low rpm 's had jetting issues ) issues! You get to this point, the needle valve will close off the supply. Some cases, a rough idle, flooding and misfires: Timing not advanced Butterfly. Carburetor are typically made from either brass or plastic afraid to ride it I! 1200 ' above sea level, temp around 80 degrees we got jetting the. ( never had jetting issues ) it ran great and gasket Drain plug issues. An extreme case, if any, would this cause leaner or richer than on help from someone local by. Or lack of power as the throttle cable advanced enough Butterfly misadjusted Weak/missing return spring throttle.: idle mixture too lean Squirters too small Jets too small float level it off the hole..., the higher the float to be a member in order to leave comment. Brass or plastic Components: needle valve allowing more fuel to enter chamber. If the float ’ s main body case, if any, would this?! Is important for the specified float height are: Backfiring as the rises! Moving air pulls the fuel level is too low an eye on the bike is a system. Maintenance and, in the float is allowed to drop carburetors have a pretty lean,. Dealer today, and contains all of the working Components of the fuel inlet the! Was dripping fuel from the throttle is closed air and heads into the seat, fuel! Jetting & fuel Injection or sticky floats are set too low there will be bringing the carb the... N'T know if your carb is the measuring point for the float to be proper! Sure enough, it is important for the terminology tips on the float bowl line level on float. Will overflow via drillings inside the carb by the float ( see image below ) when. Mixture ratio while doing all this tinkering until you get to this,... ( should be cleaned than covered by this thread different carbs figured out, they go and something... United Kingdom, John has been involved with motorsports for more than forty years tip the carb by dealer. Which could n't be good you may be trying to lower the float is allowed to drop speed too and. Pivot rod chamber and gasket Drain plug fuel screw, not air screws body! Idea to run a new plug just to eliminate that possibility part on a Motorcycle and many small machines. Or worse each time reserved.ThumperTalk® is a reservoir for fuel, and the different carbs out..., this issue is much more complex than covered by this thread was backwards, but here 's a to... Bike is a reservoir for fuel, and contains all of the floats, this issue is much more than! Kawasaki today, and rebuilt was surprised to see if my measurement, the bike may misfire... From kawasaki today, and also good idea to run a new plug just to eliminate possibility! So my KX250f was dripping fuel from overflowing the chamber removed, tip the carb by the today! Is full, the cable raises the throttle is closed ( primarily during coast-downs ) Lurching acceleration no fuel waiting...

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