Originally Posted by 8541Hawk

and what are they really for?

Well I did ask another member to post this up but I guess it has been left up to me.

This topic has been covered more than a few times but IMHO there are still some misconceptions about what they really do and if you should remove them or leave them in place.

Now I will say I do understand why they are questioned. In fact, if you look at the old Sports-Twin archive that Greg post on here a while back, you will see i asked that same question in early '98.

In fact I believe I was the first one to raise the question. Yeah I was a carb guy even back then.

So after looking at things I pulled them off. This was in my DynoJet and K&N days, so it also made pulling the carbs just a touch easier and i was pulling them quite often.....

Anyways, I ran it like this for around 4-5 months. Then I decided to hook them back up to see how it worked. What I found and didn't expect was that the bike immediately started running better. It took the throttle cleaner and was just smoother.

So then I spent a bit of time figuring out what was really going on.

Well first lets cover what they don't do. The most common misconception is to prevent carb icing. The last time this was mentioned the example of aircraft "carb heat" was used.

On an aircraft (yes I was a light aircraft pilot back in the days when I had some extra $$) the carb heat comes from an airbox mounted on the exhaust manifold. You select either the "fresh air" which is out side air or "carb heat" which draws from the aux airbox and yes you loose power.
The thing here though is the air is heated before it is drawn in.

Now look at the system on the bike. It is heating the carb. Now if you were doing this to prevent icing, first you would need to look at the flow rate through the carb.

We could sit here and do all the math but with my quick calulation (feel free to correct me here, it is early and I might have missed something) is that at 5K RPM with our displacement of 996cc you need to move around 10 liters per sec of air\fuel mixture through the engine.

So then you would need to do more math to figure out the flow in feet per sec through the carb. To make the point here easy to follow lets use a simple example. Lets say the intake track in 12" or 1' long (this is also having the entire length of the track heated, not just a small section)
and you have a flow rate of 10 feet per sec. (Now the flow rate on the bike will be much higher than this)

So with our example you have a 1' long heated intake and a 10 feet per sec flow rate. That gives you 1 sec to heat the air up. See how that just will not work. In order to make any change in the incoming air temp you would need to supply vast amounts of heat.

Now if they are not for icing, then how about emissions. Well the honest answer here would be yes, though there is a but to this part.

They help emissions by lowering the amount of unburnt fuel being pumped into the exhaust (which the PAIR valves then finish off in a stock set up, that is what the "popping" is) but that also increases fuel economy and power, so it might not be all that bad....

So what they are doing is heating the float bowl. This causes the fuel to atomize easier and also stay in suspension far longer.

To give you an idea on how this works here is a quick read on heating the intake and what it can do: Henry "Smokey" Yunick -- Fuel vaporizing carburetor system

While most is not really relevant to the set up on this bike, the most important part is this “On the flow bench and on the dynamometer, we’d pull out a sample of air-fuel mixture mixed by the standard carburetor, and you couldn’t punch a stopwatch fast enough before the mixture started to separate into a liquid and air again. But, when the mixture goes through the entire heated process and then through the homogenizer, it’s 20 minutes before it starts to settle out”.

So while this set up doesn't use the entier intake heating set up. Just heating the fuel will allow it to stay atomized for a longer period of time.

So how the system does work is that it flows heated coolant above the float bowls until the thermostat opens. Then it shuts off the flow.

At that point the engine should be producing enough heat to actually heat the carbs up and do the same job. Just run the bike hard for 30 -45 min and then stick your hand in there and you will see what I mean.

So in closing there are advantages and disadvantages to both set ups.

With out them, the bike will not pull as crisp or take throttle as well until the bike is completely warmed up. Though you do end up with less possible points to have a coolant leak from.

With them attached, the bike runs better but the carbs are a little tougher to pull and you might, and the key word here is might as I have never heard of one, have a coolant leak at one of the fittings.

The one other thing I can add is that if you have run without them for a while, try hooking them back up for a day..... You just might be surprised.

Also, once again there was a request for a "cut away" view of the carbs....
Well I guess i am the only one left with a good vtr cut away....

and while the carbs are not that clear, you can blow it up and clearly see that there is no water jacket around the venturi, they are solid. So that should put the whole "icing control" possibility off the table....
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Damn I ramble on a lot.....

Originally Posted by johndaroza

can some one show me a photo on the crab heat lines and were it goes into the water pump?

Thanks

Originally Posted by ZERO

My 2002 has no such heater or lines or any place where one ever was.