throughout the years i have heard of some people running their carb heaters and some not. I have never run mine before without problems but i was just curious about what other people do. I have heard it may cause damage (piston scratching) so i was thinking about running them this year. Just looking for some advice. 
I've ridden is -48C and I have never ever used mine. my engine has almost 9000 on it with no issues!
tntmax
Member
i run mine only after -20 or so and when i am plowing through deeeeep snow, never had any problems in 8 years...
staggs65
Moderator
mine are off all the time no probs, but i don't generally see big temp swings either
hereismylife
Active member
There is somewhere I read where after a certain temp you should turn them on/off. I just don't remember....
staggs65
Moderator
the theory is to turn em on when it gets colder so you don't have to rejet
From what I remember,Yamaha first started using engine coolant flow to heat carbs on some 570 Exciters. They did not have it on the VMAX4s[4 x TM33s].
When the 1997 SX700s first showed up with the TM33 flat slides, with their high intake air velocities, there were a lot of issues with the carb throat air passages icing up in warmer snow, rain, and higher humidity conditions. When you accelerate air through a ventury or over a wing it cools as it expands.{Bernuolli's Theory} The moisture in the intake air flow would then freeze on contact with the below freezing carb throats and/or air bleeds[like freezing rain], this would cause the sled to go "pig" rich during idle + part throttle conditions and they wouldn't start after being shut down after these conditions.[just like carb icing on carbureted aircraft]. Yamaha added the carb heat on the 98/up SRXs and 99/up SX/SXRs to keep the throats warm to stop iciing from forming or to melt the snow/ice that did form.
Unlike heat risers on cars + carb heaters on aircraft, Yamaha heats the carb not the incoming airflow so I don't believe running the carb heat on will richen up the mixture enough to avoid rejetting.
I only run my carb heat when carb icing is at greatest potential. +5c to -10c high humidity, rain, wet snow, playing in the powder or any time I figure the throats are icing up.
JM.02c
When the 1997 SX700s first showed up with the TM33 flat slides, with their high intake air velocities, there were a lot of issues with the carb throat air passages icing up in warmer snow, rain, and higher humidity conditions. When you accelerate air through a ventury or over a wing it cools as it expands.{Bernuolli's Theory} The moisture in the intake air flow would then freeze on contact with the below freezing carb throats and/or air bleeds[like freezing rain], this would cause the sled to go "pig" rich during idle + part throttle conditions and they wouldn't start after being shut down after these conditions.[just like carb icing on carbureted aircraft]. Yamaha added the carb heat on the 98/up SRXs and 99/up SX/SXRs to keep the throats warm to stop iciing from forming or to melt the snow/ice that did form.
Unlike heat risers on cars + carb heaters on aircraft, Yamaha heats the carb not the incoming airflow so I don't believe running the carb heat on will richen up the mixture enough to avoid rejetting.
I only run my carb heat when carb icing is at greatest potential. +5c to -10c high humidity, rain, wet snow, playing in the powder or any time I figure the throats are icing up.
JM.02c
Last edited:
linemech31
New member
sideshowbob has hit the nail on the head here. However i have used mine to comp for jetting as well. On = richer off = leaner. How much of a difference? I could not tell you but i have never burnt a yamaha piston.
tntmax
Member
you can for sure tell on a warmer day that if you have them on, your machine will run "fat", then shut them off you will notice better performance!!! try it sometime
I allways have mine on to be on the safe side. Owners manual says to use it below 0deg.C/32deg.F, I only turn mine off when temp. is warmer than 5deg.C/41deg.F or else it runs to rich.
The actual situation for using the carb heater is when the air temperature and humidity are within 10 degrees. It doesn't matter how hot or cold the air. When they're within 10 degrees of each other is when ice has the most potential to form in the throat of the carb. I would agree that heating the carbs and not the air entering them is basically useless, so just consider the carb heater a 'defroster', after-the-fact.
Last edited:
staggs65
Moderator
i guess i would agree that the intended use is to help with ice up, but i disagree that it doesn't affect jetting in anyway, you're also heating the fuel which is atomizing with the air and heating up the air/fuel mixture, it's the same principle with airgap intakes on cars, if it had no affect there'd be no victor jr, rpm airgaps, brodix, keith dortons, etc... designed with an airgap between the engine and carb. i'm not suggesting it's a solution to rejetting, but it does affect it, again mine are always off
GOOD INFO!!!! Thanks!!!Mtn-Track said:
Mine are always ON.. Let me tell you why.. If there was NO NEED for them,, YAMAHA would NOT have spent,,lets say,, $20.00 per sled TO FIT THIS HEATER SYSTEM ON THE CARBS.. apparently THERE IS SOME KIND OF icing OR ATOMIZATION ISSUES with this system which warrants the use of heaters.. There is also a situation which warrants a SHUT OFF VALVE so you can choose to shut off the heaters for SOME REASON or the other... Like I said before,,, YAMAHA would NOT SPEND MILLIONS of dollars to fit these heaters on the carb circuits if they were USELESS... Lets find out the REAL REASON for these and lets TURN THEM ON and OFF as the engineering designed.. Can SOMEONE look in an OWNERS MANUAL and see the REAL USE and NEED for these heater circuits????????
The manual says to turn it ON if the ambient temp is below 0C (32F), then immediately under that in a "Caution" tab, it says to turn it OFF if the ambient temp is above 0C (32F). That's about all it has to say.......on page 5-14 of the '05 version.
I also mis-stated my last comment. It should actually be DEWPOINT, not 'humidity'.....
I also mis-stated my last comment. It should actually be DEWPOINT, not 'humidity'.....
Last edited:
Mtn-Track said:
X2... and the ambient air doesn't have to be below freezing. I've seen t-body iceing during cold weather testing at 38 degrees F.
Interesting points + discussion!
I still think Yamaha installed the carb heaters on these carbs primarily to combat carb iciing. Also I must agree with comments that heat to the carbs will cause a richer condition, especially at low sled speeds, higher outside air temps, and lower intake flow. I would think as vehicle speeds increase, air temps drop, and higher intake flow, the warmer carbs would have less time to effect the mixtures.
I think Yamaha says turn them off above 0C [32F] because they don't want that extra heat to the engine especially raising crankcase + subsequently piston temps.
Its hard to say how close the dew point + actual air temp have to be to create a carb iciing situation but generally within 3C the humidity is getting very high and iciing is almost guarenteed in my experience.
I still believe anything above 5C is getting to the point where iciing is less likely[but not impossible] because I dont think the air pressue drop will cause more then a 5C drop in temp, in the small carbs, to get the air charge below freezing
This is all interesting stuff and we would likely need someone with an engineering background with expertice in this area to get the true + accurate solutions...maybe someone like the Yamaha guys that stuck them on these sleds! LOL!
JMO
I still think Yamaha installed the carb heaters on these carbs primarily to combat carb iciing. Also I must agree with comments that heat to the carbs will cause a richer condition, especially at low sled speeds, higher outside air temps, and lower intake flow. I would think as vehicle speeds increase, air temps drop, and higher intake flow, the warmer carbs would have less time to effect the mixtures.
I think Yamaha says turn them off above 0C [32F] because they don't want that extra heat to the engine especially raising crankcase + subsequently piston temps.
Its hard to say how close the dew point + actual air temp have to be to create a carb iciing situation but generally within 3C the humidity is getting very high and iciing is almost guarenteed in my experience.
I still believe anything above 5C is getting to the point where iciing is less likely[but not impossible] because I dont think the air pressue drop will cause more then a 5C drop in temp, in the small carbs, to get the air charge below freezing
This is all interesting stuff and we would likely need someone with an engineering background with expertice in this area to get the true + accurate solutions...maybe someone like the Yamaha guys that stuck them on these sleds! LOL!
JMO
Last edited:
If the Yamaha engineers explained it to us,, probably NONE of us would understand,, 1st, because they probably would explain it in JAPANESE and 2nd,MOST OF US would STILL not understand it.. I think the "venturi effect" and humidity around 32F would induce ICING in FRONT of the venturi and around the little metering jets in the "air horn" of the carbs.. Restricting the air/ fuel mixture would somehow create a LEAN CONDITION,,,,, OR,,, when it's VERY COLD outside, (lets say BELOW ZERO) the heated carbs heat up the fuel and create a RICHER condition and help with LEAN BURNDOWNS!!! Yamaha jets their motors REALLY RICH to prevent WARRANTY WORK with burnt down motors... Maybe the really cold weather OR the humidity FREEZES around the "air horn" and creates a LEAN CONDITION,, which YAMAHA does NOT WANT... Remember,, it's about the almighty $$$$$ ( or YEN) to Yamaha engineers!!!! Thats part of being an Engineer!!!
staggs65
Moderator
lmao
you kill me
Last edited:
OK, so I'm an engineer and pilot. This is how it works in the realm of an aspirated aircraft engine and how it relates to the coolant heating of the Yamaha carbs;
The majority of normally aspirated (carb) aircraft engines are updraft with the carb below the engine, out in front. Like I said in my earlier post, carb icing is an issue whenever the temp and dewpoint spread are within 10 degrees, not as likely at 50 degrees F as 20 degrees F, but still a possibility! An aircraft carb has a diverter valve on the front of the carb that can be switched over to draw air from around an exhaust manifold. This heated air is also what is used for cabin heat. When you do this, however, you loose some engine RPM and ‘power' since you are now drawing warm (less dense) air into the carb and also losing the ram-air effect in front of the carb. Does it change the air/fuel mixture? You bet it does and the result is power loss. You DO NOT want to spend much time with the carb heat on in an airplane as it's only intended to be temporary, and only long enough to clear out the carb ice. This is due to the richer fuel mix that can fowl the plugs and the natural thing to do is lean out the mixture (which you can do in a carb'd plane) to compensate for it. But, if you shut the carb heat off in that condition the engine immediately goes lean and will either stall or seize the engine, or both! Air cooled aircraft engines are also REALLY sensitive to thermal shock.
Now the Yami set-up. Can you imagine the warranty disaster they would have on their hands if they produced a sled with a rider-controlled carb AIR heater valve? It would also adds lots of extra weight to have the additional set-up of the exhaust heat exchanger, plumbing, and valving. So the easiest and safest method? Just run heated engine coolant through the carbs, and stipulate that it either be on below 32F or off above 32F. Though not anywhere near as effective as aircraft carb-heat, it will help to reduce carb icing and minimize rich/lean issues with the air/fuel ratio. Since a sled engine rarely stays at a constant high-rev state, the heated carbs will have a chance to clear out any ice that may be building up when you let off the throttle and reduce the mass flow of air into the carbs. Unless you're on the ragged edge of being lean, the temperature difference between having the carb heat on vs. off should be almost insignificant, especially at higher RPM's. The air does not have the residency time in the carb to significantly alter it's temp, thus density.
In short: If the dewpoint is between -10C to +30C, and the temp is between -20C to +30C, carb ice can be an issue.
There. That's the story as I know it and I'm sticking to it!
Oh, and my carb heat valve is always OFF! The air way up high is usually far too dry to be an issue. You lowlanders may need it though...
The majority of normally aspirated (carb) aircraft engines are updraft with the carb below the engine, out in front. Like I said in my earlier post, carb icing is an issue whenever the temp and dewpoint spread are within 10 degrees, not as likely at 50 degrees F as 20 degrees F, but still a possibility! An aircraft carb has a diverter valve on the front of the carb that can be switched over to draw air from around an exhaust manifold. This heated air is also what is used for cabin heat. When you do this, however, you loose some engine RPM and ‘power' since you are now drawing warm (less dense) air into the carb and also losing the ram-air effect in front of the carb. Does it change the air/fuel mixture? You bet it does and the result is power loss. You DO NOT want to spend much time with the carb heat on in an airplane as it's only intended to be temporary, and only long enough to clear out the carb ice. This is due to the richer fuel mix that can fowl the plugs and the natural thing to do is lean out the mixture (which you can do in a carb'd plane) to compensate for it. But, if you shut the carb heat off in that condition the engine immediately goes lean and will either stall or seize the engine, or both! Air cooled aircraft engines are also REALLY sensitive to thermal shock.
Now the Yami set-up. Can you imagine the warranty disaster they would have on their hands if they produced a sled with a rider-controlled carb AIR heater valve? It would also adds lots of extra weight to have the additional set-up of the exhaust heat exchanger, plumbing, and valving. So the easiest and safest method? Just run heated engine coolant through the carbs, and stipulate that it either be on below 32F or off above 32F. Though not anywhere near as effective as aircraft carb-heat, it will help to reduce carb icing and minimize rich/lean issues with the air/fuel ratio. Since a sled engine rarely stays at a constant high-rev state, the heated carbs will have a chance to clear out any ice that may be building up when you let off the throttle and reduce the mass flow of air into the carbs. Unless you're on the ragged edge of being lean, the temperature difference between having the carb heat on vs. off should be almost insignificant, especially at higher RPM's. The air does not have the residency time in the carb to significantly alter it's temp, thus density.
In short: If the dewpoint is between -10C to +30C, and the temp is between -20C to +30C, carb ice can be an issue.
There. That's the story as I know it and I'm sticking to it!
Oh, and my carb heat valve is always OFF! The air way up high is usually far too dry to be an issue. You lowlanders may need it though...
Last edited: