question for you dyno boys, CO v Fuel/air ratio.

[gadgetman]

how do you measure fuel/air ratios other than by analyzing exhaust gas?

[eibargum]

No gadgetman, the ones i,ve seen measureing F/A ratio,s also take the reading from the pipe, i believe the CO metherd is just another [older] way of doing it, both metherds depend on the skill of the operater as speed demon says. Chiselspeed do use the CO metherd and very well too but i suspect thats down to martin having done it for years. I first asked the question because shortly as a gas fitter iam going to have to buy a Gas Analyser, these read CO levels and i,ll feel alot better buying one if i can also find a use for it in the garage in conjuction with a rev counter and temp gauge, just for altering needles and slides etc. Another question for you dyno boys, what would you consider a safe A/F ratio for an air cooled cast barral compared to an air cooled more modern nicersill lined alloy barral. Thanks for all your replys lads .

[sean brady scooters]

you would think......cast barrels need richer mixtures to aid cooling.........and that alloy barrels would require less due to the fact that alloy is supposed to dissipate the heat better......................sometimes this is the case.........but not always..............
although a lot of new performance kits (high revving ones ) are made of alloy.........they do in fact have MUCH less cooling fin areas..........and so even though they are alloy.........there cooling properties are compromised ............

[eibargum]

Sean, i would have thought that cast barrals would have required a richer mix than alloy to aid cooling but i take on board what your saying about the cooling fins. I notice no one as come back with any anser,s to my queery regarding what A/F ratios you guys are aiming for, is this because you dont like to share such info in public [which i understand as thats how you make your living,s] or do you all have your own preferences and so theres no definate anser.

[drunkmunkey6969]

The question can't be answered in a specific manner, because there are too many variables.....you have to take each scooter, its spec, condition, use and owner into account.

At mid range to top end 12.7:1 is a theoretical minimum safe benchmark for two strokes, but we richen some right upto 11:1....it all depends what the customer wants, safety/performance etc, condition of machine, and what is the spec....24 degrees ign/16 degrees ign, alloy ported race tune, cast iron stage 4 touring tune, Clubman/JL4, Mikuni 35mm/Delly 24mm, squish/comp ratio, is it a cut down with 11 stone solo rider, or is it a full bodied tourer that goes everywhere two's up with luggage etc, etc.

Plus at tickover and low revs (1000rpm-3000rpm) the scooter needs to be leaner than 12.7 to allow crisp tickover and take off, but once revs start to climb, A/F needs to take a nice curve towards the richer safe spots, but anything leaner than 12.7:1 at the mid-max revs section starts to worry me and i look for adjustments according to the variables outlined above.

Diablo.....do you do anything differently??

[Diablo]

Like you depends on the customer and the bike.
You've seen Edens fuel/air charts done here. We have had them leaner(which I think they will take) but one factor many forget is that unless the customer comes and sees again in winter you have to jet for the whole year.
What I mean by this is that if you jet the bike on a hot sunny day you have to guess how much the mixture will lean off on a cold misty one. This is difficult but means that you have to er on the side of caution.
As you rand Sean rightly say the incoming charge cools the piston which is an important factor.
Some pistons grow more than others. Malossis grow like b@5t@rds which is why they often have a .005" clearance out of the box and also why more than a few Pollosis seize up giving my beloved Polinis a bad name

[eibargum]

Thanks for replys, Dan, Sean and Diablo , can i throw my set up into the ring, if i turned up, 15 stone, RB230, franspeed tourer TMX 30 PJ, usully travel one up around 60ish [so are lass can keep up] when out on my own 70-80mph when conditions allow, not out much after Brid [october] usully in garage , what A/F ratio would you guy,s look to acheve, please dont recomend a gastrick band .

[drunkmunkey6969]

Well as we use a bosch wide band lamba sensor to attain air/fuel readings.......i haven't ever had to use a CO meter, and certainly not on a stationary machine, so my point is...... i dont think just revving your scooter in your garage will work, you need to put the engine under load....which is the whole point of a dyno/rolling road, even more so with brake loading.

And if the CO meter you get is portable, and can be operated 'on the fly' then you need to go out and get readings on a run, and note the CO % at different speeds and at different throttle positions etc, but if its a static unit in a garage, then i suspect the readings wont mean much without engine load. Having said that, I'm not sure that making a note of CO % readings, speeds and throttle positions whilst riding on an open road is even a good idea from a safety perspective.

I'm not really happy offering up a suggested stoich reading without seeing your scooter, but if pushed, i'd say that if you pitched for 12:1 under load, at mid-maX revs, then you wouldnt be far off from a safety perspective..........£35 on a dyno is much cheaper, easier and safer though.....

[eibargum]

Your dyno,s cheap Dan , its been dyno,d a number of times, the last time [not at a scooter shop] being when i took the 35 off and fitted the 30 and useing the F/A ratio metherd, i jetted were i,d thought i,d be safe [needle 3rd clip and 260 main 80 PJ] only to find it was very lean and showed 27.8 BHP and around 13 F/A ratio, after going up 20 on the main and another clip position this dropped to 12.5 on the F/A ratio and 26.79 BHP and 20Ft lbs and thats how it was left [ too lean] ive since gone up another 15 on the main and lifted the needle 0.5 of a clip trying, to get it nearer 12-1 F/A ratio, and without any noticable loss in power, though i would think it,ll be down around the 25 BHPish by now, i,d love to stick a probe up the pipe and see what it reads CO% on the road, when i have to buy a gas analyser i,ll try and rig somthing up on the bike. Your right Dan, a dyno at a scooter shop is cheaper and less worrying when you come away , you live and learn.