Dynojet A/F Meter

brewsky · Post by **brewsky** » Mon Jul 04, 2011 5:19 pm

Another run today to test another (identical) carb I picked up on ebay.

Same jets and settings except needle at MID position instead of previous setting of one notch richer than mid.

Results:

Idle...............13.1-13.5
1/8................14.0-14.5
1/4................13.0-13.5
1/2................11.5-13.5
3/4................13.0-13.5
WOT..............12.0-13.5

Off to 1/8 throttle stumble was all but gone, and off/on throttle transitions at all openings were smooth.

I did locate a smaller main jet to try, but decided against it on this run.

Looks like the needle dropping also significantly leaned out the WOT ratio.

I guess it's not that surprising as about 1/4" of it still remains in the needle jet at WOT.

The acceleration improvement in high gear seemed noticeable.

More later.

brewsky · Post by **brewsky** » Sun Jul 10, 2011 6:05 am

Local shop had another dyno day yesterday, so I got a chance to check the A/F readings against the dyno sniffer.

You only got 2 pulls per bike, so I had one done at 1/2 throttle, and one at full throttle.

Blue lines are 1/2 throttle and Red are Full throttle.

jensen · Post by **jensen** » Sun Jul 10, 2011 4:30 pm

Hi,

Nice curves, especially the full throttle curve. The mixture tends to lean out a bit in the higher regions, and is a little too rich in the middle regions, and maybe you need another chain or chains.
I would try to lower the needle one groove, and try a slightly bigger main jet.

The torque curve is nice, but is goinf down very quick, and that's because the power curve is hollow

Earlier I explained the "lean" peak in the lower regions, this is due to opening the throttle a little too quick. I think opening at 1/2 throttle was a little more gentle.

Do these figures differ a lot from the direct readings you get from your device ?

Jensen

brewsky · Post by **brewsky** » Mon Jul 11, 2011 4:53 am

Jensen,

The readings from the dyno are close to those observed from the meter.

If you look at the last table in the above post, the 1/2 throttle varied from 11.5 - 13.5,
and full throttle from 12.0 - 13.5 on the meter......pretty close to the dyno readings.

I was surprised that lowering the needle one notch resulted in a whole percentage point increase in the WOT A/F ratio.

As it is right now, the bike is pretty smooth and rideable, with the A/F in the 12.5 - 13.0 range at normal operating rpm's. It is only approaching lean at highest rpm's.

I may try one size richer main and one notch lower needle as you suggested.

I am now confidant the meter is accurate and its reaction time is quick.

It still shows an instantaneous lean peak between off and 1/8 throttle, but it's effect is not nearly as noticeable as it was before I lowered the needle.

What is interesting to me is that my first dyno a couple years ago did not show the increase in A/F readings with RPM increase.

Check out my 750 run at the end of this post for my next jetting challenge:
http://forums.sohc4.net/index.php?topic=91089.0

jensen · Post by **jensen** » Mon Jul 11, 2011 5:25 am

Hi Brewsky,

Sometimes one notch is a too big step, I prefer going up and down with a third notch, just by adding rings under the cir clip. But make sure the rest is ok (air filter, ignition etc.) When seriously going in to the carb the rest should be immaculate, especially with a dream, which is very sensitive for needle hight and air filter issue's (as you now know).

You should definitely try a slightly bigger main jet, since leaning out with an air cooled engine in hot weather climbing a hill is something you don't want. Piston skirt failure and small end bearing issue's will reveal itself.

If I would have to work on this bike I should try a bigger main jet, to get the mixture around 12,5 from 7000 rpm and up. After having that fixed I would find a needle setting to accomplish a straight midrange mixture from 3000 to 7000 rpm around 13 or so. I would also experiment with the float hight to achieve that (steps of 0,5 mm to start with) to see what the influence is on the mixture.

Again, the wobbling on the curves are due to chain slack and / or a bad chain, this is costing much energy thus power. The dream is a 360 crank with a symmetric ignition sequence, so I expect a smooth curve.

Jensen

brewsky · Post by **brewsky** » Mon Jul 11, 2011 6:56 am

Jensen,

I have been experimenting with float height somewhat, and have it now set at 28mm from the gasket surface. That was to try and offset the overly rich idle which could not be corrected with the air screw. (Incidently, that equals 26.5mm from the carb body cutout, and aligns the float with the jet holder level ((jet removed)) as with LM's line of sight method for CB's)
See here: http://www.honda305.com/forums/viewtopi ... 6&start=10

After reading numerous posts on float level measuring reference, the definitive answer is still elusive.

The Honda Shop Manual refers to the height "H" which is the distance between the bottom of the carb main bore and the actual fuel level in the bowl, but does not state what value it should be.

What value and reference do you use for float setting for Dreams?

jensen · Post by **jensen** » Mon Jul 11, 2011 12:38 pm

Hi Brewsky,

My reference for the float hight is the midrange with the standard needle hight when that is ok, I go further with the main jet, and when that is save I go further with the stationary jet and air screw. This is a iteration process until I'm satisfied. I never differ more then 1 to 1,5 mm minus / plus from standard value of the float hight, because otherwise I screw up the way things are meant to be (air bleed holes).

My settings are 0,5 mm lower then standard for my dream, but don't forget, I'm at sea level, and riding in a sea climate (humidity is at least 50 % or higher during the summer). These carbs are sensitive to atmospheric conditions when you want to maximize the way the bike performs (and I don't mean peak power, but more what the Germans mean with Laufkultur).

I'm glad that your data isn't much different from what the dyno showed, now you can rely on your data without having second thoughts about the accuracy. Since you're higher then sea level I would raze the whole curve a bit by setting your float a little higher, in steps of 0,5 mm, having the needle in the standard position. When the mid range is good, try a bigger main jet to get the bike a little on the rich side above 7000 rpm.

The Honda references are guide lines, and in no way these settings are good for all the dreams all over the world. You can differ from these guidelines, but not for the midrange within the permitted needle range with the needle shape that Honda provided.

Like I said earlier, try to get the midrange a little leaner, and the top range a little richer. As for the stationary part, and picking up from stationary, you should measure your NOx and other related burning gases. If your stationary circuit doesn't react on the air screw, remove the spring from the air screw and try again.

I do like your courage to play with the carb settings this way and I really appreciate what you are trying to achieve here, I really do. Be careful not to lean out the mixture too much, by taking small steps at the time. Don't force or hurry to much, as you have your on board method of measurement.

Jensen