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E: Engine Comet Mongrel



Cyborg

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VOC Member
It has an Alton, so 12V no problem. In my "some day I'm going to use that" drawer, I have a similar digital voltmeter and a couple of O2 sensors. Never could get used to calling them lambda sensors. Perhaps from working with the Japanese? Easier to pronounce O2 I suppose. I just need to buy a bung. Not sure why I didn't add one to the list when I placed my order at http://www.bungking.com/o2-sensor-bung/ I saw them on there.....bought a bunch of alloy fittings for the oil & fuel tanks (thanks to Oldhaven for the link).
 

Cyborg

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VOC Member
I used a sniffer up the tailpipe on a local comet that was running very rich. Marked the throttle openings on the twist grip and took if for a ride, rich here, very rich here, etc.. After about three or four trips "around the block" followed by jets changes (only one at a time) we got it very close. It requires 12V to power it up. When you get the mongrel running we could try it if you want......

I tried it on the TTR but with a too long too small exh pipe and could not get a reading. I suspect that there was too much turbulence at the end on the pipe. It now has a bigger shorter pipe and goes waaaaaay better but haven't had the chance to take it to a track again for testing...
My heartfelt thanks for saying when and not if.
Must be a compact gas analyzer if you can take it with you.
 

davidd

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Make sure the sensor is in the correct location. Some want it 8" from the valve. Some have trouble being in a straight portion of the pipe as they work better on the outside or the side of a curve. Cars often place them 40" from the valve as they have lots of primary tubes.

David
 

vibrac

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Yes our comet was about 10 inches down the exhaust pipe on the side nearest the timing case it has an M8 screw bunged in it when not on the rolling road
 

eglijim

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VOC Member
A lambda sensor will definitely save you a lot of guesswork concerning all carb components. The sensor plus M 18x1.5 mm stainless thread and plug is easily found at Ebay, same with a little digi voltmeter as shown on the BMW damper knob, sensor under the gear box. 0.50 Volt is perfect lean, up to 0.70 V OK, above is too rich. For 6 V systems you carry a 12 V battery to supply the sensor heating, four wire type, for bikes so you can do real road tests ! You will be amazed how far from perfect a stock carb can be on a classic.

Vic
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View attachment 24790
If using this system to set up a twin, would you suggest a pair of sensors(switchable) before the pipe junction so you can check each carb individually ?.
 

oexing

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You are quite right, basically you´d need two sensors per two carbs, but it is not practical on the Vincent when you like to hide the permanent M 18x1.5 weld-in thread. Best place seems to be in the ex pipe just before it enters the silencer, in horizontal orientation - I guess. You will choose the heated four wire sensor type as on a single or twin there is not enough heat at that distance from the cylinder. I´d get new needle jets and needles anyway as these components can wear and when doing road tests you change any components in both carbs with same sizes of course. That should be close enough even when having only one sensor per two carbs like with the BMW setup.
These exhaust sniffers, are they the CO or CO2 testers ? You would not find them at small costs with battery power and small sizes to be used for bike road tests ? The O2 sensor plus voltmeter is only around € 30.- so no big deal to have it on the bike for some time. I am still busy with a Bing carb configuration on one Horex 460 , no spares for that type of Bing so this will go on for a while tweaking carb components for smooth operation at all conditions.

Vic
 

chrislaun

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I like the idea of fitting Lambda sensors as I'm rubbish at setting carbs up properly, I've two twins and I'm sure I can get hold of some old pipes so could mount two sensors part way down before the pipes join and swap back to the "good" pipes once I've got the carbs sorted
Has anyone any recommendations as to what sensors I would need so I could get everything made and set up over winter ready to fit.
Chris.
 

chrislaun

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That's an awful lot more money and complexity than I think I need or am prepared to spend, I don't need any recording or data-logging, Lambda sensors on ebay are £10 upwards and digital voltmeters are about £4, I'm just not sure which Lambda sensors would be usable.
I've got twin 5" clocks so two small voltmeters can be mounted there virtually in line of sight and I have the twistgrip already marked at closed, 1/8th, 1/4, 3/4 and full throttle.
So all I would need to do is ride at a previously decided steady throttle opening up a steady gradient and glance at the voltmeters surely.
Chris.
 

oexing

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VOC Member
Chris, the four wire types are best on a motor bike as down at the far end of the exhaust pipes temps are too low without heating. Two wires for heating from 12 V plus two wires for the voltmeter. The operating range of these sensors is narrow, you want 0.50 - 0.70 V with a good carb setup, below 0.50 is a bit lean and above 0.70 it is getting rich. I would only fit one sensor, you change carb components with same sizes on both carbs at a time - good enough. The ss M 18x1.5 mm thread can be welded easily without showing from the outside, oriented horizontal pointing to the clutch, permanent, no blueing of the chrome to see with TIG welding.

Vic
 

timetraveller

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I'm a great believer in 'science' when it comes to this type of measurement and so am totally with Chris on this. Two lambda sensors up near the exhaust ports with two separate metres sound ideal but do any of these gadgets require a voltage stabiliser? On a 12 volt system then the volts could be anywhere between, say, 10 volts and 14+ volts so do these systems have there own built in voltage stabilisers or is this something to be wary of?
 

Cyborg

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VOC Member
I may take a leap and try the one in the second link. It's for the Comet, but even if I used it on the twin, I don't think I would leave it installed. On a twin, I would just do one cylinder at a time. Plugs for the O2 bungs are cheap and plentiful. If I get one, it won't be until spring before any sort of racket comes out of that engine, but I will post the results if and when that happens. As for voltage, it's the voltage generated by the O2 sensor that it is reading. The battery voltage would be for the heater and lights.

I just read some info that states the newer wideband sensors do rely on voltage input.

By the way... thank you oexing. Reminds me of the many times I'm racking my brain to figure something out and some kind soul saunteres up and points out the obvious. It actually makes me want to slam my head in the door a few time to clear the cobwebs.
 
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Cyborg

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VOC Member
In a blurb below the eBay listing, they do mention a "laser etched calibrated resistor in the sensor connector body". I guess the question is why.... to match the meter they are using, force you to buy replacement O2 sensors from them, or maybe that's the way the Bosch sensor comes off the shelf. The comment was relating to a question about whether or not you could change the sensor connector. My guess would be that is the way the sensor comes from Bosch.
 

oexing

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VOC Member
Well, basically you can aim for the ultimate perfection. So two sensors may seem to be a must on a twin carb engine. But then you are dealing with fifties carbs and their limited scope of fine tuning: Main jet, idle jet, needle, needle jet, slide with its cut out. There is no acceleration device on these so in the end you will opt for a slightly rich setting for max power and no hickup when wringing the twist grip for acceleration. You will soon find out that you had enough of trying various settings and components and accept a good compromise. And for that a single sensor will do fine on a twin carb engine. Or would your target be the highest possible fuel saving like in car manufacturers rolling road tests to be issued for motor journalists ? I did use O 2sensors to sort out puzzling behaviours on some engines after running out of ideas. I cannot tell in all moments if the engine is too lean or too rich while doing a test ride. I had funny effects on a Honda Clubman when I discarded the air filter box and mounted a bell mouth to the rubber diaphragm Keihin: Only after I placed an action cam behind the carb I could watch the slide jumping up and down half an inch at certain power settings - hopeless for road use. The Keihin was dumped and a classic Dellorto went on and with a little help from the O 2 sensor the Clubman does what we expect.
A simple four wire sensor at 20 Pounds will do the job for your orientation towards a nicely going bike. The single sensor thread in the pipe is plugged after testing and is not visible to bystanders normally, and even so, what could be wrong ?

Vic
 

chrislaun

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Yep nicely running is all I'm after, you're probably right one sensor would do, I can only give it a try and see.
I'll still try and get some old pipes in case I want to try two though.
Chris.
 

oexing

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VOC Member
In that case you can go a bit leaner for road use of course. But even so, you will like a richer setting for best power in all conditions and most of us will not be very interested in maximum mileage per gallon. I was just saying that it is not too critical to have definitely one sensor per carburettor for best results, with same jetting in both carbs you will be quite close to optimum. With some bikes it is a bit of a hassle to get access to carbs for adjustments and changes so it is a question of perseverance how far you will go with striving for perfection in all conditions. One sensor per carb may provide all needs for that perfection - but it is another question how long your perseverance will last while fiddling with jets, needles, slide cutouts when doing road tests. It is great to have access to a rolling road so you can have the fuel tank off for tuning. One of my friends has got one in his private shop but I prefer to test on real roads so I can find a reason for short trips around home. Otherwise I don´t do much of motorbiking without purpose - living in my workshop most of the time instead.

Vic
 


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