Exhaust gas analyser

[JezzaPeach]

Hi all
Probably wishful thinking!.....Does anyone know if it would be possible to use an exhaust gas analyser, like they use for car MOTs, to adjust idle mixture, and if so, what readings would look like?

[Rob62]

It could be done but the best way to analyse the gasses is to put it on a dyno, preferably somebody you know and trust and is into his classic bikes. You need to analyse the gasses at various engine loads and speeds to get it right... I recently had one of my classic 2 strokes on a dyno, the level of info and setup that can be achieved is amazing... there’s no way you could match it with traditional tuning methods. Fortunately the dyno belonged to a good friend of mine who specialises in setting up classic 2 strokes. I was never keen on the idea until i finally bit the bullet but now I am a massive convert.

[JezzaPeach]

Many thanks Rob. I may know of somewhere locally.

[SteveW]

I read something years ago about using an old Lambda sensor to do this, basically the output voltage of the sensor is proportional to the mixture.

[JezzaPeach]

Thanks Steve, I may have a tinker to see if it works on the pipe end. Wheeler dealers retro fitted one to a classic Honda car which partly prompted me wondering!

[K2-K6]

Thanks Steve, I may have a tinker to see if it works on the pipe end. Wheeler dealers retro fitted one to a classic Honda car which partly prompted me wondering!

Was that the Civic they did in USA ?

[JezzaPeach]

Yes I think so. A yellow one. I guess maybe a sensor needs to be nearer the manifold, but if it’s mainly for idle balance not sure if it would work at the pipe exit. Also may need to be “wide band” which appears to be 4 wire type, and there is a 2 wire type.

[K2-K6]

I think they are just placed at front end on cars because that's where the cats are, so looking after mixture as close to cat as possible.

Some have used them at pipe end to give themselves reading as you ask (can't immediately find link to one) but seem to work.

Have you got a particular requirement to observe idle mixture? as most carburettor setups don't need it when set correctly. That's ordinarily if you're running a std setup for intake etc.

The Honda idle setup routine does effectively do this though (target mixture) if carried out correctly,  but by observation rather than outright measurement. It's an interesting little routine that's in their manuals as it effectively does what a fuel injection system adopts in optimizing the idle mixture.

I've an old stand alone mechanic "gas tester" that works quite well as it firstly calibrates against ambient air, then reads out how the exhaust compares to that. Fairly effective for what it does,  but of course you've no way of checking and logging readings when under load and moving.

[JezzaPeach]

Many thanks, I have a couple of rather sooty plugs, so I thought it would be interesting to compare. I have balanced the carbs using vacuum gauges so everything else seems pretty well in order. That’s interesting I’ll take a look at the manual on the idle settings, I have just used the standard 1 1/2 turns. Thanks again.

[K2-K6]

I think it was Seamus? in here posted some figures for a 500 that were obtained via mot equipment, which showed quite significant variability from cylinder to cylinder. 

They are obviously pretty small volumes, with just small physical changes making quite a difference.  But I'd of thought the main mixture would be more likely to give you general plug colour variation which would not clean up fully when running at idle speed.

As mentioned above,  someone good and experienced with a dyno would be invaluable to give more in depth picture of what's happening, especially if you can log figures for each pipe.

Are the brass jets etc Keihin?

[JezzaPeach]

Many thanks I will look for a local service. Yes I think all original. I’ll give it some more decent runs to see if it improves. My 2020 few ignition issues probably didn’t help. Kind regards

[gtmdriver]

I used to use a Gunson Gastester when I had an oilhead BMW and it was a bit fiddly to use but worked well. After a few tries though I found that tuning the idle mixture by ear got me to exactly the same settings as the gastester.

[K2-K6]

Same here

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Had my one for many years and used a lot but still works fine.  As it has a calibration routine it still seems perfectly repeatable and worthwhile for the OP as second hand they don't cost too much and really easy to use.

[Skoti]

It would be good to know what the correct C0 meter idle speed readings should be.

Anyway could you not measure the readings on the cylinders that have the correct spark plug colours and then set the other carbs to match?

Provided your exhaust silencers are not interconnected  I'm sure that would be possible with a meter similar to what K2-K6 has just mentioned.

good luck

Skoti

[JezzaPeach]

Many thanks, some very helpful advice.