cn250 Carburetor Heater Comp  By  scooter (Read 4,464 times)

just guessing, but it looks like the carburetor water heater (unused) on lots of scooter carbs. On yours, are there any tubes or hoses connected to it? If it has been not connected, I wouldn't worry about it. More experienced minds will hopefully jump in here..

That carb heater piece is no longer used on those carbs. As a matter of fact you can take it completely off it is held on by one screw.

Scooter, I have to bow out on this. But I feel your pain. I've tried to research that carb and part, and I just find no definition on it. Every schematic shows it, but no one explains it's use..Hopefully, someone with that carb setup will jump in, or Alley will have some info on it..

gee that rates with the cordless extension cord .

John

Thanks.  According to Alley, it is only for the enricher circuit.  Since there was a vacuum on the line that goes toward the engine, I assume the water would have run from the radiator, not from the engine side so, as he says, until your radiator was warm, the water in that line would be cool.  I would have thought bringing the water out of the head would have been more effective if heating the carb were the goal.  

The line going to the engine is going into the thermostat housing, bypassing the thermostat.  It appears the coolant would have to flow past the temperature sensor, so the system could, theoretically, sense the temperature of the coolant without the thermostat open.  I don't know how complex these systems are but maybe that would have let a circuit know when the water was warm, to then turn on the enricher valve to shut off the enrichment circuit?  That would certainly make more sense than trying to heat the carb with cold water.

Blue arrow, line going to thermostat housing.



I went back and looked at my carb.  The temp sensor wire and the enrichment valve wires are crimped together in one harness.  I think would indicate that they are sold as a set and work together as a system.

I thought about that, myself, but what I found so far are two things.

One, which I wrote about above, is that the system seems to be made to let the enrichment valve know when to turn on, after the engine is warm.

Two, I read that the reason for the plastic cap on top of the enrichment valve is to keep it warm, so that when you start a warm engine the enrichment valve will still be "on", or at least more ready to be on, when you restart.

This suggests that, in addition to regulating the enrichment valve, the other purpose of the heater comp(ensator?) could be to heat the area of the carb where the enrichment circuit is, meaning your enrichment valve would stay warm longer after shutting the engine down, improving warm starts. 

(For anyone who doesn't know it, the enrichment valve shuts OFF the extra fuel when the unit itself is turned ON.)

As long as the engine is cold, it would be a good thing to keep the enrichment valve turned off. These simple setups we have on most scooters appear to be a timed system, unless there is some feedback mechanism I have not found out about yet. The enrichment valve comes on as soon as the scooter does, so the circuit is going to close after X minutes regardless of whether the engine is still cold or not. Not good if you are driving in the dead of winter. Its only compensation would be how long the wax or oil in it stayed warm after the engine was shut off, via that plastic cap on it.

That would make this heater comp an innovation, which would allow an engine to keep running rich until it was actually warm, no matter how long that takes.  It would also help keep the enrichment valve warm, via all of this water heat transferred into the body of the carb while running, after the bike was shut off, changing the enrichment valve, from a mere timed device, to a part of a closed loop "smart" system.

I noticed, on my 150cc, which was air cooled, that I had to let the bike warm up longer in the cold or it would have trouble idling until it warmed up. (It started, idled fast, then slowed down after the allotted time for the enrichment valve to set in, but it died on me at the first stop sign I came to.)  The problem may have been that my enrichment circuit closed too soon, a problem this heater comp would have solved.  For someone in Florida, not a big deal, but if you live somewhere where it's really cold, this heater comp may make a noticeable difference in performance.

I'd bet it helps hot starts and I'd like to test the enrichment valve, to see if the thermo-sensor turns the enrichment valve on and off.