Dynojet A/F Meter

[brewsky]

Hi Brewsky,

On the C78 it was done slower, proportional to the rpm, because of the direct slide.

Jensen

That is what I am looking for, and to be able to at see the results and correlate them to the actual throttle position (and thus which circuit is in play). The circuit in play is not dependent on RPM, but throttle position.

My point is that unless you instruct the dyno operator differently, you will get a result based on a variation of RPM with the slide wide open, and as a result, a reflection mostly of main jet only. And that does not duplicate most real riding conditions...only those for max acceleration.

I'm not sure about this, but I believe Dynojet Dynos are inertial type, and calculate HP and torque from measuring the time it takes to change the rotational inertia of the drum between different RPM values. If so, could it actually measure HP or TQ at a steady RPM value? And wouldn't the power values at any given RPM be lower on a slow, leisurely run than a WOT run?

However, the A/F ratios should be more accurate and reflective of actual riding conditions if the acceleration is done slowly thru the RPM range.

Forgive my carburation OCD, but I can't deny it...I'm looking for group therapy now!

[jensen]

Hi Brewsky,

You won't find many members for the group,

Jensen

[teazer]

Most Dyno runs are basically WOT from as low as the bike will stand and what is being examined is power and A:F on the main jet.

What you really want is a series of runs at different throttle openings to build a 2D map.

You could do that by marking the throttle drum or use a pin in the grip and run it all the way up at 1/4 and then repeat at !/2, 3/4 and then full throttle.

Any other way does not give very accurate results with slide carbs.

[jensen]

Hi Teazer,

You suggest that the A/F curve shown in this thread (from the CB450 K0 and C78) is only a reflection of what the main jet is doing ? Are you saying that the explanation I gave about the different area's in the A/F curve is not correct, and is dictated by the main yet you run ?

If that is true, would that lead to another choice of settings, and if so, how would these settings differ ? Looking at the curve's of both bikes, what changes should I make and where ?

Can you show me some of your 2D dyno data and explain to me how to implement the optimal settings that work for every road situation ?

When you (re)program a motor management system with a power commander the data is 2D actually 3D and up because ignition timing and gear are the other D's), and is done at a dyno.

A dream doesn't have a motor management system, no 4D or more mapping ability, so no choice of how the bike is managed, btw, what would be the point in finding a 2D mapping if you cannot use it ? Because a 2D mapping will suggest different settings for the same rpm throttle position in different (road) situations, and can be conflicting.

Really, the setting you will find won't differ much from the data extracted in a controlled dyno run, while the throttle isn't pulled at WOT at once. A good operator knows how to find the data he's looking for, and regarding the health of my engine it's a very good approach of a setting that work in most road situations,

Jensen

[brewsky]

Most Dyno runs are basically WOT from as low as the bike will stand and what is being examined is power and A:F on the main jet.

What you really want is a series of runs at different throttle openings to build a 2D map.

You could do that by marking the throttle drum or use a pin in the grip and run it all the way up at 1/4 and then repeat at !/2, 3/4 and then full throttle.

Any other way does not give very accurate results with slide carbs.

That's the point I was trying to make, except said with a lot fewer words.
Thanks, Teazer

[teazer]

Warning: This thread is for people obsessed with carbs. :-)

Jensen, realistically it's a 3D map that you want Revs-Throttle position- A:F.

But that's too complicated in the old analogue world so Dyno operators go for a WOT run to get the main jet right. Almost every bike made and sold in the last 20 or so years for ON road work came with a CV carb or EFI. And many EFI systems use secondary throttles. On GSXR that's a butterfly with stepper motor control. On and R1 it's a slide and diaphragm.

Jetting a CV carb is a little different to a slide carb and the circuits don't apply the same way because the slide is not all the way up all all load conditions. Paradoxically that makes them easier to jet in theory and often harder in the real world.

The technique Jensen is using is valid in that he is trying to test under similar conditions in which he rides his bike and that's a valid approach.

The average dyno operator will do a run at WOT and will assume that because it's wide open that the only circuit in operation is the main jet and that's just not accurate. The needle clip position actually makes a difference all the way through the revs at WOT. Mixture is not constant at a steady WOT all across the rev range either.

What we usually do is to get the main jet close to right and look at the gas analysis. I'm not so concerned with A:F, but with power figures all across the curve against unburned fuel and CO and CO2 and oxygen levels. That tells us what's burning and how it's burning. Then we tweak air jets and needles to get the fuel slop close to right.

Then we ride it at different throttle positions and move the needle up or down and adjust the slow jets to get the crispest throttle response. Sometimes what works best outside in teh real world is a little different to what we see on the dyno because the dyno cannot hope to mimic real world on-off throttle conditions.

What the dyno and gas analysis does for us is to get us in the ball park. I only put a street bike on when it has been modified and I want to know that it's OK to run before I melt something.

It's just another tool in the box and if we can't get on a dyno we do it all the old fashioned way.

[jensen]

Teazer,

In the past years that I worked on these classic engines I found out that a lot of these engines were showing severe damage. Some of this damage was caused by neglecting (mostly oil issue’s), and some were caused by the mixture, looking at the burned valves, damaged and cracked pistons.

When I was restoring the engine of my 1967 CB72 (a complete and thus expensive rebuild), a friend of my (in possession of a dyno and many years of experience) suggested to strap the bike on the dyno.

I have to admit that I didn’t take it for serious , saying it would be ridiculous to put such a bike on a dyno, because I wasn’t interested if it was delivering 18 or 23 Hp or so. But he was serious about it, and because he started working as a motorcycle mechanic in 1970, he had an interest in how the bike would perform compared with his experiences in those days with the fours.

The first run directly showed that the bike was on the lean side, and we experimented with different main jet’s and needle clip positions. Me on the other hand experimented with more modern carbs, like I described before (Yamaha RD350 carbs, and KR1 carbs). Because he didn’t charge me large amounts of $$$, we spend hours and hours on the dyno. We tested all different types of mufflers, we tested the early carbs versus the later carbs, Cl carbs without the power jet system etc.

I use the CB72 as commuter, but because the bike has not much power compared to modern bikes, it is doing WOT at least 30% of the time I ride it (highway’s). I always accelerates fast, at WOT, and still I’m passed by everyday cars.

When I use the bike for touring I have the throttle ¼, ½ or ¾ position for a longer time, I never have fouled plugs or any indication that it is running rich or lean, it pulls on command, and is breaking on the engine like it should and doesn’t overheat.

I think that the way the bike is tested on the dyno is reflecting the way I ride it on the road.
Today, I test every bike on the dyno, before I go riding on the road, to see it it’s not lean (or to rich). It gives a good indication of the status of the bike, not only max torque and power. I know I’m lucky to have a friend with a dyno close by, and most of all that he has the experience with slide carb bikes on the dyno.

I definitely don’t see a dyno as a miracle tool, but in the rights hands and with a open mindset (not focusing only on WOT, max power, and max torque), the dyno is the tool to check the basics, giving you a picture (curves) in how the bike is behaving. That picture alone is worth it.

But most of all, I don’t see the dyno as an absolute measuring instrument, but more as a relative measuring instrument. You are able to compare results before and after a modification, or just over time. That’s why it’s used for racing bikes, because these bikes are modified constantly in search for more power and torque and give an insight view in were to find it and how.

I prefer a dyno run once in a year, preferably in the spring, (not to hot not to cold, and not to dry or to humid), before the season starts and of course I compare it with other years to see if something has changed. That makes it easy to determine what is going on in the engine and act on it before the damage is done.

A run as described will cost between 30 to 80 euro, and that is money, especially today, but spreading it out over 5000 km (an average a year), it makes it worth it for me.

The other thing is that I’m interested in what other bikes look like on the dyno, because now, I have only my bikes as a reference. I have never seen any other dyno chart of a standard CB72 or a CB450 K0, or a CB400F, not on this forum, and not on other forums. The only curve I can compare is the dream, but I guess something went wrong while measuring.

So, the only “reference” I have is the chart drawn in the factory manuals, but I doubt these are really measured, other than mathematically computed by Honda. Just for fun, compare my run from my standard CB450 in the charts Honda gives in the manual, and these curves are soooo different, not only max power and torque but also the shape.

There must be someone other than me who is interested in dyno work and displaying their charts on this forum ? Teaser ? Vince ?

Jensen