My Dyno Chart

[Exhibit76]

only Performance Mod: Freedom Race Exhaust

 

So it appears Im very LEAN in the Low end (Primary jet)?

 

and comes out slightly Rich up top (which is ok, as I plan on doing an Intake next)

 

but am I reading it correctly, where I should go 2 sizes bigger on my Primary Jet?

 

your thoughts?

 

[cowpuc]

I'd fatten it up on the metering rods at least by two notches if your metering rods have e-clips.. If not, I would accomplish the same task with nylon washers (used as shims) to raise em 1.5 mm to start with.. I would also CAREFULLY examine the diaphrams for ANY pinholes - look carefully along the area where the diaphram meets the carb body under the cover.. Also,, double check for those little o-rings under each cover..

You should be able to dial out of it with the meter rods IMHO...

[BlueSky]

Going on past memory, you need about a 12 to 1 A/F ratio for full throttle operation and that appears to be what you have or richer in the upper ranges. Those diaphragms should have the metering rods completely pulled out on full throttle runs. As I remember, you need almost 18 to 1 A/F ratio for best part throttle fuel economy. Engines with O2 sensors and computer controls control the A/F ratio at 14.7 to 1 because that is the ratio where the O2 sensors start detecting O2. And that is a good ratio for low CO and low NO. NO goes up with lean ratios.

[Exhibit76]

Thanks u 2.

 

I will order extra Primary Jet sizes, but go into the Carbs looking for any leaks and if I find none, I will go ahead and up the Primary size, because that dip is pretty good and the Dyno Guy said he had it WOT and so theres something amiss in the Low-Mid range

[BlueSky]

Are the leaner peaks at 55mph and 72 when the gears were shifted? I assume he let up on the throttle when shifting and the mixture might go leaner at that point. The initial lean readings were when he first opened the throttle? Right? It might take a short time to go rich. I'm not sure you need to do anything to the carbs but I'm no expert for sure.

[Exhibit76]

The dyno operator knew I was mainly needing to see how the tune was, so he said he started 1/4 Throttle, then Rolled on through 1/2 throttle, then to WOT.

and said the DIP was at 1/4 THROTTLE, which he believed could be solved by going up 2 Primary Jet sizes.

 

*The big does feel low on power on 1/4 throttle acceleration

[cowpuc]

I am sure your Dyno op is wayyyy more with it with this stuff than I will ever be but the way I have always tuned carbs was from this understanding that I came to years ago.. Throttle shut, engine idling,, tune engine with low speed jet/air screw.. Get it spot on.. WOT = main jet sizing = get it spot on.. Anything in between is Metering Rod function.. The metering rod is tapered to produce multiple air/fuel mixes throughout the range from the moment the rod unplugs the main jet itself at idle all the way to the point the metering rod leaves the emulsion tube at WOT - then its job is done..

There are lots of metering rod tapers available - us old 2 stroke dirt bike guys (especially early KTM people) can probably remember going thru bags of those little suckers trying to get the right one so it the motor would perform cleanly and perky but not so much that she'ld burn down from mid range leanness...

Ok,, probably getting way hard to follow again... Think you oughta just follow your Dyno guy but if it were me,, I would still raise the needles and retest it just for kicks..

[MikeWa]

I have always hated the way motorcycles are dyno tested. The dyno computer converts everything to engine output making all gears look the same. Personally I prefer to see what is hitting the ground which will be very different in each gear.

 

Mike