carburetor heater

[Guest BillFoltz]

I have a question that is puzzeling me and maybe one of the great mechanics can answer it for me. What is the purpose of the carburetor heater? Do these things go bad? If one were to go bad,or if the relay were to go bad, how would you know it?

[muffinman]

If you truly do have carb heat it is to keep the fuel from freezing after it goes through the venturi's

 

I was not aware that the second gens had carb heat I will be looking at my books later to see what type heaters they have.

First gens dont have carb heat so this is news to me

Jeff

[99silver]

Really good question !, I know their purpose is to keep a constant air /fuel mixture temp for a better ignition. But I'm unsure what kind of symptom you would get if one were to fail ??

Gary

[muffinman]

Really good question !, I know their purpose is to keep a constant air /fuel mixture temp for a better ignition. But I'm unsure what kind of symptom you would get if one were to fail ??

Gary

If true carb heat were to fail on any motor that has it, you would know because the fuel would freeze up in the venturi's, causing decreased performance and possibly shutting the engine down if the ice gets bad enough.

Jeff

[derwood]

sorry for picking nits....it is actually the water in the air that freezes when the pressure drops as the air passes through the venturi. The symptoms would be poor drive-ability and stalling, particularly during warm-up or after extended cruise in cold and humid conditions.

All that BS and i've never seen heated carbs on a bike, not doubting you though, the idea may be to shorten the warm up time in an effort to reduce emissions.

P&L dave

[pegscraper]

Carb heaters are an emissions thing. If one were to go bad or a relay were to fail, you'd never know the difference, and neither would the air.

 

The Venture carbs that I swapped onto my bike have heaters in them, but I didn't connect them to anything because my original carbs didn't have heaters and there was nothing on my bike to which to connect them. The heater connector is just dangling in there. I've ridden in temps as cold as 0* many times and never had any trouble with the carbs freezing up. As long as the roads and the weather are clear, I ride. The cold temps don't stop me, and neither has a frozen carb, because it just doesn't happen. Carb heaters take, what, 15 W a piece for power, times 4? Disconnect them and get yourself an extra 60 W for lighting or heated gear.

[RedRider]

Yup, I like extra power available for electric toys. How do you disconnect them? Or is there a fuse that is dedicated to the heaters that would be easy to remove (and replace if the air Nazi's demand it)?

 

RR

[pegscraper]

You could pull the connectors off of each individual carb. Or there's a plastic connector at the front of the carbs that separates if you ever need to pull the carbs from the bike. You could leave that apart. Pulling a fuse isn't an option. The fuse that covers the heaters also covers several other things.

 

In my case I didn't disconnect it. I never connected it when I swapped the carbs. And there are no wires on my bike to connect it to.

[SaltyDawg]

Yes the 2nd Gens have carb heaters and if you are in a moderate climate there really is no need for them since they rob needed amperage from the RSV. Not really sure if you need them in colder climates either.

 

Living in NC there really is no need to use them and I just pulled the fuse. They came on at temps below 63 and would draw a good .8VDC from the electrical system. I have not noticed any performance issues with the fuse out.

[SamB]

Where did you find the fuse .which one one is it?

[BuddyRich]

Pulled this of a Ninja site but it tells you why we have carb heaters. But I suspect Yamaha ran into just such a problem somewhere and wanted to be sure the bike was an All Weather machine.

 

Introduction

 

Carburetor ice is the term for a condition where ice accumulates in the throat of a carburetor. It's most commonly associated with piston-engined light aircraft, but can occur in any engine which uses a carburetor. The Ninja 250 is susceptible to carb ice in certain conditions. Fuel injected engines are practically not susceptible to icing up, although it's theoretically possible to accumulate some ice under extremely adverse conditions.

For the Ninja 250, it appears that a range of about 20° F to 50° F (-7° C to +10° C) with visible moisture (fog or rain) can cause carb ice. Pod-style air filters may exacerbate the problem, since they can allow more moisture into the carbs than the stock airbox, however the shorter intake tract may yield some benefits when considering strictly atmospheric moisture.

If you are riding in conditions where carb icing is frequent, you can learn to predict it quite accurately by carefully observing your local weather conditions. Factors affecting carb icing include:

• Current Temperature
  
• Dew point
  
• Relative Humidity
  
• Altitude
  
• Throttle Opening (related to riding style)

For example, it has been shown that noticeable carb icing will occur at 450′ ASL approximately 90% of the time when

1. The current temperature is less than 6°C above the dew point

2. The current temperature is below 6°C (43°F), and

3. The relative humidity is high (> 80%), or it is raining, and

4. Riding in city traffic (moderate throttle openings)

Additionally, for the same altitude, it has been noted that if it is snowing big fat snow flakes, carb icing will almost certainly occur; whereas little tiny powdery snow flakes indicate that it will probably not occur. Larger snowflakes generally correspond to higher relative humidity.

[edit]

Why is carb ice a problem?

 

Carb ice is a problem because it constricts the caburetor, choking off the engine in a very literal sense. As the ice builds up, it closes off the passage through the carburetor, reducing the fuel/air mixture the engine can get. Under appropriate conditions, carb ice can entirely kill the engine. Even before that, it reduces the engine's performance enough to be dangerous in any real-world traffic situation. Carb ice is closely analagous to asthma in a living creature.

Carb ice can stall your motor, and there's nothing you can do to get it running again while riding along in traffic! The only cures for carb ice involve many minutes of waiting.

Severe carb icing on the Ninja 250 will also cause the cause the spark plugs to foul badly -- to the point where the motorcycle may not re-start even with a boost after several severe icing episodes. The fact that winter trips (and certainly carb-icing trips!) tend to be relatively short exacerbates this problem; the spark plugs will remain at least partially fouled until they are brought up to their self-cleaning temperature, which may be as high as 850°C. Running a hotter plug in the winter will help the spark plugs reach their self-cleaning temperature more quickly. The NGK CR7HSA is a hotter plug which will not fail in the Ninja 250 motor under commuting riding conditions, however we would not suggest subjecting them to track duty. It is also possible that a platinum plug would be a superior choice for an icing-prone Ninja 250, as they are designed to resist fouling.

When riding in carb-icing conditions, it is suggested you carry a set of pre-gapped spark plugs and sufficient tools to install them at the side of the road. Additionally, a pair of jumper cables which fit your motorcycle's battery are recommended, as it is not unlikely you will kill your battery trying to start the motorcycle after a severe icing episode, and it is generally not safe to try to bump-start a motorcycle in carb icing conditions (cold, wet roads, possibly with snow, probably sandy).

[edit]

What can be done about carb ice?

 

If you're riding along and the engine starts running rough or loses power, there's a chance you have carb ice. If switching to reserve doesn't cure the problem, it's very likely your carbs are icing up. On the Ninja 250, other indications are:

• You must blip the throttle and hold the engine at 3,000+ RPM at intersections to avoid stalling
  
• You must use increasing amounts of throttle to maintain the same engine speed (RPM)
  
• You smell fuel (extreme rich condition)
  
• The engine note changes to a more staccato sound (this means you are about to stall!)

The best and safest reaction is to pull over into a safe parking spot and stop the engine. Engine heat will heat up the carburetors, and they should be ice-free in 10-30 minutes, depending on build up, ambient temperature, and engine temperature. Note that in extremely severe weather (well below freezing), engine heat will not be enough to melt the ice in your carburetors, and you may need to abandon your motorcycle and wait for a warmer day to retrieve it (or have it towed to a heated garage).

Be sure to run the motor as soon possible once the ice has cleared. If you let it sit for more than an hour or two after a carb ice incident, the melting ice will rust the inside of the motor. The small amount of water caused by carb ice won't hurt your motor if it's running, although it may run rough while ingesting the water.

If you can't stop, your only choice is to try riding out the ice. Generally, carb icing is most pronounced at moderate throttle openings (1/3 to 2/3 throttle), so if you can change things so you're riding at nearly open throttle or closed throttle, that might help -- however, it could also be extremely dangerous if it causes you to go much faster or slower than the speed of traffic. Chances are pretty good that your carb will continue to ice up regardless of your throttle position, once the ice has started.

Riding an icing Ninja 250 can be particularly frightening. A mostly-closed throttle will almost certainly cause you to stall, however, you can usually re-start the engine by suddenly opening it quite wide. In order to keep the engine running, you will need to keep it at at least 3,000 RPM -- even when stopped for a red light. It will be much noisier than usual, but you must keep the engine revs up. When stopping for a light, do NOT shift into neutral, or you will not be able to shift back into 1st gear without dropping the revs dangerously low (or seriously abusing your transmission). When riding along, you may be able to help clear some of the ice by pulling in the clutch and opening the throttle up for a moment (many times); be sure to rev-match carefully before letting out the clutch or you may find your front wheel pointed skyward. Finally, you may lose/regain a single cylinder at random, potentially causing great excitement while rounding a slippery corner.

The conditions which cause carb ice (20° to 50° F and rain, snow, or fog) can be pretty miserable to ride in; you can prevent carb ice by just not riding in these conditions.

[edit]

Why does carb ice form?

 

In order to understand carburetor ice, you have to understand a bit about how a carburetor works. One of the key principles of a carburetor is the venturi, a constriction inside the carb which causes air to flow faster. This drops the air pressure in the venturi, which allows fuel to be sucked from the float bowl through the jet system. The drop in pressure also lowers the temperature of the intake air. This temperature drop is aided by the evaporation of gasoline, which is being atomized by the carburetor to burn in the engine. (Note that fuel injection systems do not have a venturi, instead relying on some variety of pressurized system to atomize fuel. This is the main reason FI is practically ice-proof.)

This temperature drop just past the venturi can be pretty amazing. In airplanes, carburetor ice can form up to 90° F ambient temperatures, and a carburetor can theoretically drop the temperature by up to 100° F. (Fortunately, the Ninja 250 doesn't seem to be anywhere near as prone to carb ice as some airplane carburetors.) This temperature drop cools the body of the carburetor. When the carb body drops below the freezing point (32° F or 0° C), any moisture in the air which hits the carb body has a chance of freezing onto it. Unfortunately, the temperature drop also tends to condense water vapor out of the air, just like water collecting on the side of a cold glass. If there's any water in the fuel, this can contribute to the ice problem. As this occurs, more and more water can freeze to the carb body, gradually building up ice on any of the carb surfaces. The more ice there is, the less air can get through.

Middle throttle openings are the worst for carb ice because they allow a good amount of air to flow (and therefore pressure to drop and gasoline to evaporate), but also present a lot of surface area on which ice can accumulate. Idle throttle gives relatively little cooling, and full throttle presents relatively less surface area for ice, as well as producing higher temperatures from the engine.

This is necessarily a brief and superficial explanation of carb ice. If you want to learn more about carburetor ice, check out some of the information in this Google search. Keep in mind that most of the information available about carb ice is airplane-specific: specific temperatures and conditions may not apply to our motorcycles, and the consequences aren't quite as dire (but almost) for motorcycles.

[edit]

How can carb ice be prevented?

 

The principal methods of avoiding carb ice are to heat the incoming air, or to heat the carburetor body. Wes has experimented with heating the carb body with some good success. Intake air is typically heated by routing it past the exhaust pipes in an airplane, and the same method could theoretically work on the Ninja 250. No one has reported attempting to use this method.

Carb heaters for the Ninja 250 are available, both in the form of electric heaters (there's a cavity on the Ninja's carbs for electric carb heaters), and engine-coolant-based heaters. Neither form is easy or cheap to find, and either one will require considerable work to implement on the Ninja 250.

Wes spent a considerable amount of effort designing an automatic circuit to control his electric carb heaters. More information about this circuit can be found in this thread, as well as on the project page Wes put together. Further information can be found by searching the board for carb heater. This is an advanced project involving the creation of circuit boards, and will require considerably more electronic knowledge and skill than the average rider possesses. This isn't required for electric carb heaters to work -- it just makes them turn on automatically versus having to switch them on manually.

If you are interested in implementing a carburetor heating system in your Ninja 250, acquire two Kawasaki P/N 99995-1422 kits and post on the main Ninja 250RC forum. You can then discuss implementation details with Wes. Note that as of this writing (Mar 2006), even a minimalistic solution will require decent design/hacking skills with automotive electrical systems, and the ability to remove/install your carburetors. The 99995-1422 kits are very expensive, however Kawasaki has been "dumping" them around the $10 mark for a couple of years now (it is suspected that they have excess stock and no demand -- they were built as a retro-fit for the KVF-400).

[pegscraper]

My mistake. I was looking at a Royal Star wiring diagram, which shows that the fuse which covers the carb heaters also covers the horn, turn signals, and brake lights at least, and maybe another thing or two. When I looked at the wiring diagram for the RSV, it turns out there is a dedicated fuse for the carb heaters.

[KiteSquid]

Yes, from the wiring diagram, if you either remove fuse 37 or relay 38 it will disable the carb heaters.

 

I however will not disable this system...

[SaltyDawg]

Where did you find the fuse .which one one is it?

 

The fuse is located behind the right lower faring. You have to take the faring off to get to it. It is dedicated to the carb heaters only.

[Tartan Terror]

I pulled the fuse a year ago. The way I see it, after the bike is proper warmed up there will be enough heat built up under the tank to keep the air warm. I have experienced no difference since I disconnected the system and I dont intend to re hook it up. If its that cold its gonna be in the garage anyway. (Below freezing) The fuse is located inside the rt side Lower fairing. All you need to do is remove the 3 allen head screws and pull the cover forward.

[Guest BillFoltz]

Wow, the response to this question has been great! All your imput sure did sratch that itch. Now I will post another question that has been bugging me for a while and see what comes of it. Thanks, BillFoltz