Electric carb heaters - help needed

[utopia]

My Y2K M750 has electric carb heaters.
I don't know how well they actually work, but they're at least a bit tidier than the earlier oil fed heaters, and presumably they work a little better otherwise why change?
Until this year I hadn't had much trouble with carb icing...but then again I don't use the monster much during the winter and when I have, its usually been on the better days.
Recently though, I've suffered serious carb icing, usually when the weather has been damp, but not that cold.
I've dosed the tank with pro.fst, and I'm expecting that to sort it, but I would like to check that the electric heaters are still working properly. After all, they must help somewhat, so I might as well use them, even if I still need the pro.fst as well.
I've confirmed that there is a live feed to the thermal switch, but beyond that I get nothing. I imagine this is because it wasn't cold enough when I did the test, so the switch was open.
Does anyone have any suggestions as to how I might check the thermal switch, and the heaters themselves? I have a small multimeter, but I'm not a natural electrician.
If I temporarily bypassed the thermal switch, does anyone know if the heaters would get hot enough to check them by feeling for warmth in the carb bodies? ....or might this burn out the heater elements by running them continuously for too long?
Thanks.

[Dookbob]

A simple continuity check between the connectors on each carb and earth would verify that the heater elements are OK or not. As long as there is fuel in the float chambers then bypassing the thermo switch temporarily shouldn,t burn them out, but I would go for the continuity check, you cant damage anything that way.
Where is the thermo switch situated on the bike, now that you have raised the subject I will check mine out too.

[utopia]

Thermal switch is right next to the heater in the right-hand carb body.

[Dookbob]

I wondered what that was, thanks

[Dookbob]

Checked my carb heaters this afternoon, had a look at the wiring diagram first. The wiring diagram shows a thermal switch in the circuit between the fuse and the heaters as you would expect. I removed the two heater plugs, one of them has an earth tag which connects to the loom and away to earth. So the heater plugs basically heat up the whole of the carb body, but I couldn,t find anything like a thermal switch anywhere near the carbs, unless the heater plugs themselves contain a cut out device. I have continuity through both heaters and power to both, plus continuity from the earth tag to the frame and engine block so everything is as it should be, but I would like to find the thermal switch wherever it may be lurking. Looks like I might have to chase the wiring from the fusebox. I,m sure that what you thought was the switch is in actual fact the heater.

[utopia]

I'll have another look at mine.
What I thought I'd observed last time was......
Heaters are supplied via blue wire from posn. 6 in fuse box.
LH carb has a single blue wire/spade connector. I assumed this to be the heater, and I assumed it was earthed through its own casing.
RH carb has two blue wires, one spade connector (heater again), and one bullet connector to a unit right next to the assumed heater. Seemed like the bullet connector had to be the thermal switch. My wiring diagram shows no other connections in the blue circuit.
My test was simply to connect via a 12v bulb from the bullet connector to earth.....the bulb lit when I switched the ignition on, so I assumed that confirmed a supply to the 'switch'. The same test from the spade connector (heater?) to earth didn't light the bulb, so I assumed either 'switch open' or 'switch broken'.
To be continued.....

[Nickj]

I found a little sensor up by the headlight, just behind and nearside, I assume it's for the carb heaters.
As it's warmer I've dropped back to normal fuel, Shell advance has been OK this winter down to below -10. This morning we weren't a happy motor though, a bit too much moisture in the air I think

[Kato]

Don't spend to much time on them, as in full working order they are two shades worse than useless, if carb iceing is a problem use pro FST in your fuel........

[Dookbob]

With a little clue from Nickj I now have it sussed. The naturally simplistic nature of wiring diagrams dont take into account where on the bike different components are situated. Power is from 7.5 amp fuse in main fusebox feeding the thermal switch which is positioned near side behind headlamp (thanks Nickj).
Thermal switch feeds two heater plugs one on each carb (blue wires).
Off side heater plug carries a connector on its side which goes to earth ( black wire ).
So if you want to bypass the thermal switch for testing purposes, you need to disconnect the switch behind the headlamp and place a temporary link accross its connectors.
I was confused to some extent through thinking that the thermal sensor was reading the temperature of the carb body, but of course its reading the ambient air temperature, hence its location near the headlamp. I,m pleased I got that one out of the way before bedtime, otherwise I would have been getting " are you still awake, thinking about bloody motorbikes again". You would think that they would get used to it after 50 years wouldn,t you.

[Dookbob]

I take Kato,s point though about the usefulness of these heaters, but If they are there , then its nice to have them working.

[utopia]

Agreed.
Wiring diagrams always fool me that way.
And, if the heaters are there, they might as well be working, even if only to reduce the cost/qty of dosing with pro.fst. ...and anyway, I'm curious.
At first sight, I was surprised that the temp sensor is located away from the carbs. After all, its the low pressure in the venturis that creates the freezing in the first place...it seemed sensible to measure the temp at source, as 'twere......and also maybe to thereby switch the heaters off again when carb temp (as opposed to ambient temp) was high enough..and so on in thermostat fashion.
I'll go and peer inside my headlamp shell now. The beam height needs raising a fraction anyway.
I'm still not sure what the second, ie bullet connector is going to on the offside though.
To the shed....

[utopia]

Ah, yes. I see the little blighter now.
And sorry, my earlier comments about bullet/spade connectors and switch location were clearly complete gobbledegook, based on not quite remembering what I'd seen the day before.
I might see if I can hoick it out of its hideyhole, and give it some sort of 'ice or hairdryer' test.
Thanks, all.

[Nickj]

I'll go and peer inside my headlamp shell now. The beam height needs raising a fraction anyway.

A few strips of thin ply under the front wheel will raise the light nicely :)

I had a 600SS with the oil heated carb bowls, not really sure if it did anything particularly useful. Same with the electric gizmo's

[utopia]

A few strips of thin ply under the front wheel will raise the light nicely :)

It's ok. I pumped the front tyre up a bit. :look:

[Dookbob]

I removed one of my carb heaters today , just for the crack, I put 12 volts through it on the bench, in 5 seconds it was too hot to touch. I,m sure that they MUST make some difference to the iceing problem, even if they are not the complete answer.

[utopia]

Nice one.
I bet you lay in bed last night thinking about that one, eh?..........:rolleyes:
I too, am of the opinion that they must help somewhat, and are worth having even if only to reduce the amount of pro.fst that you have to buy.
Hence my suspicion that the thermal switch may have failed recently on my bike, as I haven't suffered serious carb icing in previous years....though I have used the monster much more this winter cos the Dommie's off the road.
I promise to do my bit, and test the thermal switch....post to follow.
I'm waiting a couple of days though, 'til my ebayed Aviacompositi dash/revcounter arrives. (sorry again, Jim).
You can rest assured that I'll be straight on the case as soon as the postie delivers.

[gary tompkins]

I had a 600SS with the oil heated carb bowls, not really sure if it did anything particularly useful.

Nope - they are crap as well in my experience

Total waste of £160 that would have been better spent on Pro FST :banghead:

[utopia]

Removed and tested the thermal switch last night. It seems to be working ok.
Results as follows :-

At shed temp, as removed.....continuity....resistance across switch = 0.2 ohms.
Switch hung over radiator for 15mins....no continuity.
Switch put in freezer compartment of fridge for 5mins....continuity, as before.
Switch left to warm slowly at room temp....still continuity after 45mins.
Switch then held over radiator....almost immediately switched to no continuity.

During the last test I actually heard the switch click as it operated.

So it appears to be working, though I was a little surprised at two things :-
1) That the switch was in the "on" position at shed temp, even though last night was not that cold at all.
2) The long time the switch took to operate when warming up at room temp after coming out of the fridge.
Basically though, I think I'm happy that the switch is operating.
I'll test the rest of the system tonight.

[utopia]

Yesterday evening I continued the tests....
Removed both carb heater elements.
Connected each in turn to a 12v battery via an indicator bulb.
The bulb lit on each occaision, though not very brightly, despite the battery charge being confirmed at around 12.7 volts.
After about 30secs connected up, I could feel no heat at all in either of the elements.
I then checked the resistance of each element with my little multimeter....one was about 35ohms, the other more like 50ohms.
This difference rings a small alarm bell......??
Then I connected them back up to the 12v battery and left them for at least a minute, after which time I could still hardly feel any heat in them at all using my fingers, but when I put them on my cheek I could detect a definite warmth...though it certainly wasn't too hot to touch for as long as I liked.
I'm now thinking that maybe my heaters are working, but not quite as they should be.
I rang JHP to check the price of new elements, though I'm still not certain that I need them. After an initial question as to the very existence of electrically heated carbs, I eventually got a price and part number (13440321A)....£35 each..........:eek:
I guess if yours heated up to "too hot to touch" in 5secs, Dook, then mine must be duff...and the difference in resistance between the two elements perhaps points that way (I've got no idea what their resistance should be).
At that price though, I'd like to know more before I spend the cash on new ones, though I guess I could just buy one to start with, and see how that checks out.
Or maybe they're available cheaper direct from Mikuni, or a specialist supplier. (any suggestions, anyone ???)
Or I guess I could believe what everyone says, ie they're not worth the trouble.
But my curiosity is well and truly aroused now, and it would be good to know once and for all whether they actually do help with icing.

I'm still not sure what the second (black) wire connected to the tag on the RH heater is. It looks like an earth, but the heater earths through its case, and there is no corresponding wire to the LH carb/heater, just the blue feed wire, so I'm assuming they earth through the carb body to the engine etc.

Hey ho. .... Still to be continued.

[utopia]

Now i've finally figured the wire to the tag next to the RH heater....it is an earth, cos the rubber carb mounts insulate them from the rest of the engine so they need a separate earth.
I'm assuming that both carbs are linked, metallically speaking, so there is no need for an earth on the other carb.
I did say that electrics aren't my strong point, didn't I ?

The rest of the wiring all checks out, so I'm concluding that either the heaters are sh1t anyway and don't do much good or, as I suspect, my heaters are duff.
I've done a search for replacement carb heater elements at a sensible price, but met with a complete blank so far.
If there's anyone out there who has elec heaters and fancies measuring their resistance, I'd be most interested.

I was also once again surprised that the thermal switch was in the 'on' position at shed temp all day today, and it was really quite a warm day for the time of year. It seems that the heaters are on for a much wider range of conditions than I'd thought, ie even on a mild day like today when I would never have expected carb icing to be an issue.

[Dookbob]

Look at it this way, if the heaters are on when they dont need to be , so what. But if the heaters are off when the temperature is low it can be bad news. So yours are OK. I dont think that there is much that go wrong with a heater plug, which would explain why no one sells them.

[Dukedesmo]

Look at it this way, if the heaters are on when they dont need to be , so what.

Cold air is denser than warm air so an engine would make marginally more power with cold air - well until it's so cold that it freezes...

[utopia]

Cold air is denser than warm air so an engine would make marginally more power with cold air - well until it's so cold that it freezes...

Yes. I remember a report in a mag in the 70s where a respected engine tuner (Helmut Fath, I think) had a two stroke yamaha running on a dyno and poured cold water from a watering can over the crankcases to cool the incoming charge, causing an immediate increase in power.

For now though, I'm assuming that my heaters are in fact switching on when they should, even though that might be surprisingly early.
My concern is that they just aren't reaching the required temperature due to a deterioration in the elements themselves.

[Capo]

Carburettor icing is a result of three factors:

Relative Humidity - the amount of moisture in the ambient air
Ambient Air Temperature
Dew Point - The temperature and which the moisture in the air begins to condense into water.

The graph below indicates the probability of icing at various conditions. Descent power may be taken as low throttle openings

http://ibis.experimentals.de/images/carbicingfromcaassl14.gif

As the system only measures ambient temperature and as can be seen from the graph icing can occur at temperatures of 30C. The operating set point of the sensor takes this into account

[utopia]

Thanks, Capo.
That confirms what I was thinking. Its nice to have some hard data though.

Perhaps my best bet is to find a helpful dealer who has the heater elements in stock and will let me test their resistance value before I buy them. Trouble is, I suspect that no-one wiil have them in stock and I'll have to put in a special order, which would be a bit cheeky if I then decided that mine are ok after all and I didn't need to buy the new ones.