nc35 : jetting help. with dynochart

[fourfingers]

hi all. I´m posting this for a friend of mine. His 35 is running flat after 12k.
This is his setup.
MJ F120/R122
SJ 35
pilot 1 1/2
Needles stock
Foam one layer
Airbox stock
HRC tray
Tyga exhaust with round can (not maggot)

Any input is welcome.

Here goes the chart

[Cammo]

It's running lean as throughout the whole rev range.

To get it running right use a standard filter and jet with 112's all round.

A filter like that will need approximately 128-132 main jets, but will need dyno tuning to get it right, all foam filters will flow differently.

He'll get better rideability using the standard filter and the smaller jets mentioned above, that's what I would recommend. This change in power/rideability will be much better than it is now!

[stevie]

before he goes changing all that try going up in the main jets to 126/128 & see how it reacts, you will need dyno time to get the fine tuning rite but if you can get it close then it wont need so much dyno time. he may find some after market needles might help with the transition from needle to main jet, i think rick oilver sells hrc replica needles, i you can go for the "A" needles and set them on the top/longest setting, it may help but get the main jets rite first, unfortunatly it is try'll & error, keep a record of what changes you make and the result of those changes, im supprised the dyno opperator dident recomend some changes. try going up in the main jets first & let us know how it reacts & we can go from there, he could allso try getting a pair of short vellocity stacks from a breakers and get rid of the longer ones, but try one thing at a time, good luck.
i run 35 carbs on my 30 with the hrc kit, air box & air tray, i run a filter with one layer of foam and i run the "B" needles on the top clip, 155/158 m/j, hrc emulsion tubes slide springs & vellocity stacks.

[fourfingers]

Thanks for the replies.
Stevie, I think the graph isn,t clear enough. I have deleted the first run.
The afr shows around 12 to 13:1 , on the rich side Id say( I always get confused with this one: 14.7:1 should be optimum, and over that lean?), and the power curve starts wobbling from 12k up.
Any other suggestions?
One more thing, my friend has a set of hrc needles (not installed though)

[MexicanGringo]

A lower ratio like 11 is rich and a higher like 16 is lean. Looks like its running a bit richer after 12k which might explain.. The mixture for the rest of the curve is ok if 12.5 is considered optimal achievable ratio after idle,tho the ideal thoughout the rev range is 14.7 with normally aspirated engines,but this is impossible to achieve with a carb.. So he needs to reduce fuel or add air at 12k. Maybe another run or 2 on the dyno is needed as well

[Jon]

At the risk of starting a bunfight inertia dynos are not briliant for setting mixtures with an O2 meter as the run up time is so quick.
They are great for doing back to back comparison runs to see what difference a change makes.

The squigly line is a common sign of running a little lean, I would try some bigger main jets and see how it pulls, especialy as the 1st run was a fair bit leaner and a lot more erratic.

Up that far in the rev range is pretty much all main jet, the influence of other carbie components are at lower throttle openings.



regards
jon

[Cammo]

Ohh err, my comments were based on the other run on the graph!

Why not just stick to a carb setup that's proven to work well?

[stevie]

i looked at that graph today on the keihin web site. the needles may help a bit but as said its realy the main jets that need sorting, which needles dose he have? as i said the "A" needles would probably be best as they are the leaner of the three choices, it will be main jets and needle taper you need to get rite. as i said try one thing at a time and record any changes you feel, when testing the bike if the main probolem is at 12k find a straight bit of road and hold the bike at 12k it should run smooth, you should be able to tell if it is lean or rich by how it reacts if it bogs down or hunts for revs, and make changes according to what you feel.

[fourfingers]

Thanks for your answers. I´ll let him know, and will try to post the results after dyno time.

[Bike_Nut]

A neat trick I learned from an ex ducati mechanic to check for lean mixture at full throttle is close the throttle slightly, and if it pulls better then your probably too lean. Worked a treat setting my NSR125