For al.
Thanks for the long reply!
Right.. you have missed or misinterpreted my point. All wind resistance, weight on bike or whatever does ,is load a motor...You are behind the lorry... you are at 1/4 throttle or whatever... you pull out and the wind causes massive drag... so what are you doing to the motor? You are loading it excessivley... Its working its socks off..heat is rising and if not set or built right det starts... There are dynos that can replicate this.. You can adjust the load watch in real time whats happening...detonation occurs-you adjust for it then replicate the run at the same rpm and same load.. check again....and adjust..
You can add increasing load to replicate the drag,the weight... and you set the motor handle these extremes. The brake isnt just a constant amount... these dynos you can add increasing amounts to replicate as much load as the motor will ever handle.
As load increases afr changes-massively-I've tested it. And I've seen it in practise many many times in the two stoke and 4 stroke motorsport world.Yes a road test is always the final check.. but the brake dyno is where we should be going.....
So what I was saying without a load device or a sound method of loading the motor the afr is pretty meaningless and its not accurate imo.
air fuel ratio on the dyno
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Hi Tony,
I've not missed the point I understand where you are coming from. What I'm trying to get across with the lorry scenario is that if a bike is slipstreaming a lorry for whatever reason it may well be running quite a few revs at a very small comparative throttle opening.
I don't agree that AFR readings are meaningless on inertia dynos. If that were so then the bikes would be miles off when they are ridden afterwards. I do agree that a degree of interpretation is needed to transfer that to how a bike behaves on the road but that is what the customer is paying me for.
I also agree that a braked dyno can replicate to a degree loads experienced on the road which is why we are looking into using ours along side our inertia dyno.
I've not missed the point I understand where you are coming from. What I'm trying to get across with the lorry scenario is that if a bike is slipstreaming a lorry for whatever reason it may well be running quite a few revs at a very small comparative throttle opening.
I don't agree that AFR readings are meaningless on inertia dynos. If that were so then the bikes would be miles off when they are ridden afterwards. I do agree that a degree of interpretation is needed to transfer that to how a bike behaves on the road but that is what the customer is paying me for.
I also agree that a braked dyno can replicate to a degree loads experienced on the road which is why we are looking into using ours along side our inertia dyno.
I agree; load devices are a significant financial add on to dyno's which is perhaps no scooter shops offer it.tony wrote:For al.
Thanks for the long reply!
Right.. you have missed or misinterpreted my point. All wind resistance, weight on bike or whatever does ,is load a motor...You are behind the lorry... you are at 1/4 throttle or whatever... you pull out and the wind causes massive drag... so what are you doing to the motor? You are loading it excessivley... Its working its socks off..heat is rising and if not set or built right det starts... There are dynos that can replicate this.. You can adjust the load watch in real time whats happening...detonation occurs-you adjust for it then replicate the run at the same rpm and same load.. check again....and adjust..
You can add increasing load to replicate the drag,the weight... and you set the motor handle these extremes. The brake isnt just a constant amount... these dynos you can add increasing amounts to replicate as much load as the motor will ever handle.
As load increases afr changes-massively-I've tested it. And I've seen it in practise many many times in the two stoke and 4 stroke motorsport world.Yes a road test is always the final check.. but the brake dyno is where we should be going.....
So what I was saying without a load device or a sound method of loading the motor the afr is pretty meaningless and its not accurate imo.
Regardless of that though, because I've reading up on google, Lambda senors do not give an accurate AF reading for 2 strokes; we all know its being chucked out the exhaust which distorts. Maybe thats why unwittingly 12:1 ratios are being targeted to compensate, it was mentioned about experienced operatrors and perhaps 14:1 's coming back seized however many moons ago gave reason for thought.
The karting world which is of course way more advanced than ours, recognise that they don't work and on set up they compensate / calculate with an EGT coupling.
I know you have to accomodate those that can't be arsed Al but setting a compromise on jetting for summer / winter doesn't make sense to me, there's already the gear out there to change the jetting with the turn of a dial depending on conditions.
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yes al and I toally agree... but if you are in the slipstream.. by this I mean behind the truck you will be at smaller throttle openings than you would expcect as you are not loading the motor... you pull out and you may find yourself at full throttle at the same speed.. you can replicate this. I think the reason for so many blown motors from inertia dyno setups is due to the operator thinking they can set up the motor simply from an inertia run.. quick road test and all well. You do know the score hence why I was pleased you said what you did at the beginning. But I think you will be very surprised when you get a brake dyno to how much motors can be 'out'.
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@ matts dad
well to be fair I do agree with al on the jetting for conditions..as air density changes as we know.
The variable powerjet is neat.. but depending how its fitted determines at what range it effects.
I think the road versions apply into the middle range tho so will work as you say..
You had a mess with these alan? Pretty cool.
well to be fair I do agree with al on the jetting for conditions..as air density changes as we know.
The variable powerjet is neat.. but depending how its fitted determines at what range it effects.
I think the road versions apply into the middle range tho so will work as you say..
You had a mess with these alan? Pretty cool.
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Its not a variable powerjet Tony, they work on induction acoustics and deliver throughout the range.
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ha.. no.. sorry i wrote it wrong.... i mean 'adjustable'. 
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I cant see them working 'throughout' the range.... They will work in a fashion depending on how you fit.. you need a certain velocity through the bellmouth to get them to draw.. hence why at lower throttle openings the carb has a small opening for its pilot air feed. The slide needs to be open to get these things working.. It depends on how its fitted.
If its the dial-a-jet system... they still work on how you fit the unit.. Just looked at their site and still the bleed nozzle is in the center if the venturi. So how would it flow with the slide closed to 1/4 throttle as there is no velocity at this point? The nozzle would have to be near the opening position. Then if you adjusted to gain at this small opening you wont see any gain higher up as the percentage of extra flow would be quite small at large openings... they have fitted to the center to the best solution.. its quite neat for sure.. it is similar to the powerjet system tho
If its the dial-a-jet system... they still work on how you fit the unit.. Just looked at their site and still the bleed nozzle is in the center if the venturi. So how would it flow with the slide closed to 1/4 throttle as there is no velocity at this point? The nozzle would have to be near the opening position. Then if you adjusted to gain at this small opening you wont see any gain higher up as the percentage of extra flow would be quite small at large openings... they have fitted to the center to the best solution.. its quite neat for sure.. it is similar to the powerjet system tho
Last edited by tony on Mon Nov 29, 2010 10:22 pm, edited 1 time in total.
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At the end of the day the scooters leaving the workshop are set up for getting to rallys and back. The feedback I get from my customers is positive so something must be done right somewhere. They are set up using a combination of an inertia dyno, an AFR meter ,road testing and experience.
Mattsdad I've read plenty on the internet as well. Racing karts are a million miles away from road going scooters.
In fact racing scooters are a million miles away from a rally going bike as well in terms of set up. What kind of scooters do you think we test here? I'd love you to come and tell a customer with a GT kitted TV running a 25mm through the airbox and a clubman all about adjustable jetting. He may well ask you if the kit comes in chrome
I'll let you come and weld a boss on his downpipe for an EGT gauge.The fact is we test all kinds of scooter here. Most but not all have a remit of not squeezing every last hp from the bike but to jet it so it runs cleanly and gets them to where they want to go and back.
I'm assuming that you travel on the motorway and fast A roads for hundreds of miles?
Just take a british summer. The air temperature and humidity can change dramatically in just one day. Someone could ride one up to a rally and two up back. The point was a large factor of safety needs to be dialed in to any rally going bike because road conditions can be so variable. This is the reason I at least aim for a AFR reading around 12. What others do I don't know but I don't think I'm on my own here.
This is backed up with road testing + thousands of miles ridden on the road every year.
You say my method is wrong and innaccurate-fair enough but I set my own bikes up and what I do is based on experience not what I've read.
Tony like I say we have got a braked dyno and have used it. We didn't have a fuel meter then but we were able to jet reasonably accurately by ear and interpretting the graphs. One thing I will say is that sometimes im thankfull we have an inertia dyno because some of the bikes we get for testing wouldn't survive a loaded power run
We have used the adjustable power jet and it works well. I'm doing some work with Oz this weekend on his Vespa and will be using one.
Mattsdad I've read plenty on the internet as well. Racing karts are a million miles away from road going scooters.
In fact racing scooters are a million miles away from a rally going bike as well in terms of set up. What kind of scooters do you think we test here? I'd love you to come and tell a customer with a GT kitted TV running a 25mm through the airbox and a clubman all about adjustable jetting. He may well ask you if the kit comes in chrome
I'll let you come and weld a boss on his downpipe for an EGT gauge.The fact is we test all kinds of scooter here. Most but not all have a remit of not squeezing every last hp from the bike but to jet it so it runs cleanly and gets them to where they want to go and back.I'm assuming that you travel on the motorway and fast A roads for hundreds of miles?
Just take a british summer. The air temperature and humidity can change dramatically in just one day. Someone could ride one up to a rally and two up back. The point was a large factor of safety needs to be dialed in to any rally going bike because road conditions can be so variable. This is the reason I at least aim for a AFR reading around 12. What others do I don't know but I don't think I'm on my own here.
This is backed up with road testing + thousands of miles ridden on the road every year.
You say my method is wrong and innaccurate-fair enough but I set my own bikes up and what I do is based on experience not what I've read.
Tony like I say we have got a braked dyno and have used it. We didn't have a fuel meter then but we were able to jet reasonably accurately by ear and interpretting the graphs. One thing I will say is that sometimes im thankfull we have an inertia dyno because some of the bikes we get for testing wouldn't survive a loaded power run
We have used the adjustable power jet and it works well. I'm doing some work with Oz this weekend on his Vespa and will be using one.
Here al.. this will interest you.. in 'road run' mode on this dyno you can add a drag coefficient value in(this is calculatable so you'd do a lambretta gp/rider for example) .. you add machine weight and weight of the wheel.. then the auto load device knows how much drag is on the machine..You can then add more load to replicate the lorry overtake if you wish.
This is the step test.. albeit a fairly quick run through.. but it shows what i mean. You dont need a egt boss.. there are other ways with this machine to see whats happening.
This gives another way of doing it..
This is the step test.. albeit a fairly quick run through.. but it shows what i mean. You dont need a egt boss.. there are other ways with this machine to see whats happening.
This gives another way of doing it..
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