Measured Air/Fuel Ratio for Optimization

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1up3down

1up3down

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In addition to my 850, I also have a 2012 fuel injected Triumph Bonneville.

After fitting aftermarket mufflers, opening up the air box, removing oxygen sensors, and having my Triumph dealer remap the ECU I asked for some dynamometer time at their shop.

After two open throttle runs up to 7000rpm my Triumph shows 61hp at the rear wheel versus 52 stock.
I am very happy with these performance modifications.

But on to the reason for my post: I received a print out showing a pretty constant air/fuel mixture of almost 15 parts air to one part gas.

This IS on the lean side, presuming the base line is 13 to one.

The Triumph service manager assured me that this leanness was in no way cause for concern (overheating) and in fact results in more horsepower than a richer air/fuel mixture, verified by his shop and many dyno runs on similar fuel injected Bonnevilles with my same modifications but aftermarket ECU remaps setting the ratio at 13 to 1.

This was news to me as I had always assumed a richer mixture meant more power, seems conversely is the truth.

I have been reading though the Mikuni Flatside Flatspot thread and was especially interested in the comments from those who solved their own jetting issues by actually going down in jet size, after first going up.

Their findings confirm my own dyno experience that maybe most of us, myself included, just assume that richer is better in terms of more horsepower and as the first attempted solution to flat spots, etc.

Seems not so, that in fact one should maybe first set up carburation on the lean side as regards needle position and main jets and then fine tune going a tad richer to see if that results in more verifiable power.

Seat of the pants jetting is often just wrong and deceiving, when compared to the relatively low cost of buying just a little time on a local dyno that also has the ability to tell you the air fuel ratio results.

I was charged only $50 for my Triumph dyno tests, now I am very tempted to take my Commando there and have them run it up to about 6000rpm to see what my air fuel mixture is with my JS flatslides and get a HP reading.
 
From memory, I thought stoichiometric efficiency for a petrol engine was 14.7:1. That being the figure at which 'correct' combustion takes place.

Therefore, power is not about being rich or weak, it's simply about being 'correct'.

I think that we generally favour richness over weakness because a rich engine will soot up, maybe hunt a bit, maybe lose 1 or 2 BHP... Whereas a weak motor may seize or hole a piston!
 
There is no doubt a lean mixture will make more power although 15-1 sounds a bit too lean. I would not rely completely on a mixture reading from an O2 sensor on a dyno. An O2 sensor can be very accurate but it needs to be designed for and calibrated in it's actual permanent environment. A tailpipe sniffer is only good for comparisons.

You will not be able to get by running a Norton leaner than about 13.5 to 1 under power. They do not cool as well as modern engines and will fail at leaner mixtures. Jim
 
I use methanol in my Seeley 850. To get the most out of it, it is as difficult to tune as petrol. The most power you get from either fuel is just before it is so lean that the motor starts destroying itself. Sparkplugs are 'read' when setting the main jets by looking for the 2mm black ring at the point on the porcelain where it joins the metal, right down inside the plug. Years ago our top riders found that the way to get a TZ350 Yamaha really competitive was to lean off, and in many cases that black ring which indicates safety, disappeared. The problem is that you have to be conscious of weather changes and adjust your jetting if necessary. Have you noticed that your bike runs much better on freezing cold mornings ? - it is probably jetted too rich under normal circumstances.
Phil Irving in Tuning For Speed,said - 'If you run methanol rich, you still get good power' - that is true, however you don't get the MOST power. A lot of guys who race using it, don't know that. I use Mk2 Amal carbs with Mikuni petrol needles on a low comp. 850 motor with 34 degrees of ignition advance. The Amal alcohol kit needles are ridiculous.
 
This all boils down to being able to *ignite* a lean mix and then to avoid such lean mix it detonates to fast. "Correct" richness is attempt to give more chance to combine with limited O2 molecules and excess fuel to cool-stifle burn rate to avoid detonation. Aircraft flyers know they can lean out enough engine temps drop for best economy cruise. Comnoz found the Powerarc 3 tap CD discharge spark is not enough to fire in hi CR mixtures so in pow wows now to convert to Plasma Blaster Ignition but w/o any extra-expensive HV supply boxes and gizmos involved.

Congrates on the Triumph tire wear upgrades working out nicely.
 
Eddie, I would never use a chemical measurement of exhaust gases to jet a bike. The way to go if you have Amal carbs, is to buy the correct length Mikuni needles in a variety of tapers - on those needles the tapers are three stage. The hardest thing to get correct is the situation at 3/4 throttle when the parallel part of the needle is just leaving the needle jet. The mixture you are looking for is where the cough due to leaness just disappears. That is set by changing the needle jet size and the needle height. Once you have that correct, the next step is to start changing the needle tapers to lean off the top end of the throttle openings. This can cause obstruction of the main jets, so if richening the mains doesn't give a change in plug colour, you know you are metering off the needle at full throttle where it should off the mains. In effect I try to run as lean as possible at all throttle openings. If I lift the needles one notch on my Seeley 850 the bike becomes noticeably sluggish.
 
Here is some food for thought. When I use methanol in my Seeley 850 (9 to one comp.) , or back when I used it in my low (10 to one) comp short stroke 500cc Triumph, I advanced the ignition by 4 degrees. My friend raced an old long stroke 500cc manx on 12 to one comp with methanol and did not change the ignition timing. He later raced a short stroke 500cc Manx on 14 to one comp. and retarded the ignition by 2 degrees.
The ignition timing and jetting to get the optimum power situation , depends on which fuel you are using and the comp. ratio. The stoichiometric ratio stuff is theoretical, it is what works in practice which is important. Just because a black box operated by a mechanic tells you something - take it with a grain of salt. I'm an industrial chemist, in my profession a major objection is about engineers misusing our black boxes. The measurement might be good for setting a bench mark (reference point), however in absolute terms - bullshit.
 
Shouldn't this stuff be for "motorcycle related discussions" cause you sure can't be talking about good ole simple straight forward what you see is what you get type Norton Commando motorcycles.

Man o man, some of this stuff is really reaching. I grant you that I can take or leave what ever I can manage to understand but holy crap, sometimes the room starts spinning and I just have to look away.

Seriously though, don't stop, (like you would) there might be something I can use there. But you have to admit, there are only few who can actually relate.

I bet a few nubes will think twice after reading these long haired scientific studies and go for something a bit more simple like a good ole Commando........No wait......what the hell is goin on here. The room is spinning!
 
My brother and I have almost come to blows when discussing how to jet 3 cylinder Kawasaki two strokes on methanol. These days it is extremely rare for him to lose a race on historic sidecar speedway.
 
So, why'd you remove the 02 sensors?
Click to expand...

because they were causing a hesitation off idle

on the newer Triumph EFI bikes, in order to meet Federal emission requirements, these bikes come stock with both air injectors right next to the spark plugs and also O2 sensors in the header pipes.

I removed both air injectors and O2 sensors as they were causing the hesitation and roughness off idle.

The guys on the Triumph online forum say that the O2 sensors effect only the first 6% of throttle opening anyway.

The air injectors poof air into the chambers to lean the mixture coming out the tail pipes, mostly at a steady cruising type throttle opening to meet the standards.

Good riddance to both.
 
Pete, it is NOT rocket science. If you want the best performance from a commando , you use standard ignition timing and lean off the mixture carefully right across the whole range of throttle openings until you get signs that the motor might destroy itself, and check that you've got excellent response under all riding conditions. If you then change the fuel or the weather changes a lot, you need to adjust for the change. I think you will find that most commandos are set too rich to cater for lazy bastards who just ride the bike fairly mindlessly - the average commuter.
 
About the oxygen sensors - surely there was provision to richen the first 6% of throttle opening? I think I would have also removed them. If they lean off uncontrollably, that is not good when you are trying to lean off sensibly right across the full range of throttle openings.
 
About the oxygen sensors - surely there was provision to richen the first 6% of throttle opening?
Click to expand...

seeming so, but this is what I was told

there is also a lambra type probe under the seat that tells the ECU the relative thinness of the outside air

By my getting rid of both the air injection system and the O2 sensors, some irritating problems were eliminated

Triumph states that aftermarket (non Triumph) ECU maps will void the new bike motor warranty, mades sense.

These maps allow one to hook a cable between laptop and bike and alter the ignition curve and air fuel mixture also.

Its all pretty cool and new stuff to play with, interesting and I learned a lot from it all.

Did I post this thread in the wrong forum as our Commandos do not have ECUs?

I don't think so as we do spend a fair amount of time talking about jetting/air fuel mixture trying to optimize our Commandos, I felt my dyno experience showing a slight overall leanness being beneficial might be helpful......
 
acotrel said:
Pete, it is NOT rocket science. If you want the best performance from a commando , you use standard ignition timing and lean off the mixture carefully right across the whole range of throttle openings until you get signs that the motor might destroy itself, and check that you've got excellent response under all riding conditions. If you then change the fuel or the weather changes a lot, you need to adjust for the change. I think you will find that most commandos are set too rich to cater for lazy bastards who just ride the bike fairly mindlessly - the average commuter.
Click to expand...


Is that like turning a bolt in the head until it strips, then back off half a turn?
 
I've been holding off wading into these shark-infested waters, but somebody might actually find the info useful, so here goes.

I use a WEGO O2 sensor to help sort out weird jetting situations. It uses a wide-band sensor with real-time display of fuel-air ratio. It does require that a fitting be welded into the header for the sensor. You can buy a kit to use it as a tailpipe sniffer too, but I used the weld-in bungs instead. It also has a data logging feature where it records the sensor reading plus another input, usually rpm. I haven't used the data logging feature yet, but the real time display is great.

http://www.daytona-sensors.com/WEGO3.html

As several listers have pointed out, that's pretty much overkill for a fairly stock Commando. If you still have the orginal or similar Amals, getting the right jetting is pretty straightforward, and the procedure is well described in many places.

Once you jump into Mikunis or Keihins the large selection of needles and jets and slides can be a bit more daunting. I bought the WEGO to use in setting up my Norton for Bonneville, running a nitrous oxide system, where a lean mixture spells instant engine death. You don't usually get a lot of runs in a meet, and the O2 sensor helps avoid a lot of trial and error changes in the wrong direction. I haven't used it for that yet, but I have used it recently to set up a couple of street bikes with jetting issues, and found it very useful. One was a Yamaha FZ600 engine with pod intake filters and an aftermarket 4-into-1 pipe. To get it right required changing pilot and main jets, and shimming the needle, and the WEGO with its real-time display was really helpful. The other was a Rotax single where I took a full-on race engine and put it in a street bike, with no changes except a new exhaust with muffler. I kept the 44 mm Mikuni carb, which is normally too big for a 660 cc street single, but with the help of the WEGO I managed to get it jetted to the point where it is almost civilized in street riding.

Using the system is pretty entertaining. You do get some transient readings when changing throttle quickly that are probably not very significant, but it is quite educational to compare how the bike performance feels to the rider against what the sensor says. As someone pointed out, stoichiometric is 14.7, but you normally want the mixture a bit richer at anything besides steady cruising. Good numbers seem to be 12.5-13.5 for idle and acceleration, and 13.5 - 14.5 at cruise. If you're running really high compression ratio on pump gas, you might want the wide-open-throttle mixture to be as low as 11.5 to avoid pinging. That was the situation with the Rotax, where ratio at WOT starts at 11.7 and creeps up to 12.5 at higher rpms. That seems to be the sweet spot for it.

Maybe a disclaimer here. These are all numbers aimed at best street hooligan performance. You might want something significantly different if your goal is to squeeze the maximum gas mileage out of a bike.

Bottom line is it's a useful and fun tool for gearheads, but not really necessary to get your Commando sorted out.

Ken
 
1up3down said:
This IS on the lean side, presuming the base line is 13 to one.
Click to expand...

14.7:1 is the optimum mixture...but it cannot be maintained throughout the throttle range. If you put an exhaust gas sensor in your pipe you will see that the burn varies depending on RPM. I'm assuming this reading was taken at 7000 RPM.

1up3down said:
This was news to me as I had always assumed a richer mixture meant more power, seems conversely is the truth.
Click to expand...

Leaner mixture will give more power, but at the expense of more heat and potential for damage. Not sure why you thought the opposite was true. When we were discussing this in the other thread, the rule of thumb when tuning for normal "street" use is to err on the rich side because too lean can damage the engine. It's not to get more power. It's a safety factor. You can only run slightly rich...plugs will foul if the settings are too rich. I use a "Plug Chop" at half throttle to test the pilot circuit and full throttle to test the main. This is not the most accurate way to do it, but if the engine runs properly through the range of throttle, and the plug color is good, then it should be okay. In some cases where you can't get the carb tuned, then exhaust gas analysis can help.

1up3down said:
Their findings confirm my own dyno experience that maybe most of us, myself included, just assume that richer is better in terms of more horsepower and as the first attempted solution to flat spots, etc.
Click to expand...

There wasn't any discussion about tuning for horsepower in the thread as I recall. I think you misinterpreted this. The discussion was about a problem at a specific RPM and whether that related to carb size and jetting.

1up3down said:
Seat of the pants jetting is often just wrong and deceiving, when compared to the relatively low cost of buying just a little time on a local dyno that also has the ability to tell you the air fuel ratio result.
Click to expand...

The methods discussed in the other thread are not "Seat of the pants". This is the common way to find the proper settings on a new carb. In the particular case you cited, a Mikuni Flat Slide carb that is larger than most used on Nortons is causing issues. There is no base line information on this combination on the web. There is very little info on Mikuni Flat Slides on Nortons. In cases like that it is a bit of a crap shoot because you have to find your own baseline. But, once the baseline is established the methods to tune the carb are the same and that may seem seat of the pants but it is the only way to do it.

Right now your method seems inaccurate, because the fuel/air mixture ratio you are using is not correct and there really isn't enough information to tell if your carb is set up right. I would want to see the readings at different RPM's along with a plug chop to see the color of the burn.
 
lcrken said:
I've been holding off wading into these shark-infested waters, but somebody might actually find the info useful, so here goes.

I use a WEGO O2 sensor to help sort out weird jetting situations. It uses a wide-band sensor with real-time display of fuel-air ratio. It does require that a fitting be welded into the header for the sensor. You can buy a kit to use it as a tailpipe sniffer too, but I used the weld-in bungs instead. It also has a data logging feature where it records the sensor reading plus another input, usually rpm. I haven't used the data logging feature yet, but the real time display is great.

http://www.daytona-sensors.com/WEGO3.html

As several listers have pointed out, that's pretty much overkill for a fairly stock Commando. If you still have the orginal or similar Amals, getting the right jetting is pretty straightforward, and the procedure is well described in many places.

Once you jump into Mikunis or Keihins the large selection of needles and jets and slides can be a bit more daunting. I bought the WEGO to use in setting up my Norton for Bonneville, running a nitrous oxide system, where a lean mixture spells instant engine death. You don't usually get a lot of runs in a meet, and the O2 sensor helps avoid a lot of trial and error changes in the wrong direction. I haven't used it for that yet, but I have used it recently to set up a couple of street bikes with jetting issues, and found it very useful. One was a Yamaha FZ600 engine with pod intake filters and an aftermarket 4-into-1 pipe. To get it right required changing pilot and main jets, and shimming the needle, and the WEGO with its real-time display was really helpful. The other was a Rotax single where I took a full-on race engine and put it in a street bike, with no changes except a new exhaust with muffler. I kept the 44 mm Mikuni carb, which is normally too big for a 660 cc street single, but with the help of the WEGO I managed to get it jetted to the point where it is almost civilized in street riding.

Using the system is pretty entertaining. You do get some transient readings when changing throttle quickly that are probably not very significant, but it is quite educational to compare how the bike performance feels to the rider against what the sensor says. As someone pointed out, stoichiometric is 14.7, but you normally want the mixture a bit richer at anything besides steady cruising. Good numbers seem to be 12.5-13.5 for idle and acceleration, and 13.5 - 14.5 at cruise. If you're running really high compression ratio on pump gas, you might want the wide-open-throttle mixture to be as low as 11.5 to avoid pinging. That was the situation with the Rotax, where ratio at WOT starts at 11.7 and creeps up to 12.5 at higher rpms. That seems to be the sweet spot for it.

Maybe a disclaimer here. These are all numbers aimed at best street hooligan performance. You might want something significantly different if your goal is to squeeze the maximum gas mileage out of a bike.

Bottom line is it's a useful and fun tool for gearheads, but not really necessary to get your Commando sorted out.

Ken
Click to expand...

Ken +1 We posted at the same time and said some of the same things :D
 
hey, thanks for extensively quoting me and then showing where you disagree Dennis

by the way, our Commandos don't run on the pure octane rating for the 14.7 ratio you maintain
in fact my figure of about 13 to 1 is right on for a "normally aspirated motor"
http://en.wikipedia.org/wiki/Air%E2%80%93fuel_ratio

For pure octane the stoichiometric mixture is approximately 14.7:1, or λ of 1.00 exactly.

In naturally aspirated engines powered by octane, maximum power is frequently reached at AFRs ranging from 12.5 to 13.3:1 or λ of 0.850 to 0.901.
Click to expand...
you seem more knowledgable about all this than me, thanks for your corrections!

appreciate your input sir
 
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