Jetting help needed! Really weird

[rallykay]

Hello everybody.

I was at dyno yesterday but wasn´t able to complete the jetting so i will go back again soon.

When i do i would like to have some knowledge from here with me so please get in and suggest!

This is what the last of the runs looked like:





The bike is like this at the moment:

full TYGA system, HRC air box (a real one!) with Piper cross filter mat at the intake, full HRC carb kit (short stacks, softer springs, and emulsion tubes, jets and needles).

The jetting at the moment is like this:

MJ 150/152,5
NEEDLES C-needles with clip second from top
Air/fuel screw according to Haynes manual

As you can see it is running dangerusly lean at arund 12K rpm dispite the big MJ:s
Any ideas to why it want such huge jets an suggestions to how to smooth the AF curve would be apretiated (to say the least)!

Thanks in advance

Kay

[CMSMJ1]

how does it work on the road/track?

[rallykay]

It pulls quite good to 10K, then you can feel that it ain´t as quick from there on.

[chrisxr]

is this a rvf or vfr?

that graph requires a little smoothing there for sure and definatly there will be power lost. The lean are is when you are on the main jet but it goes richer at the end ....... definatly emulsion tube and needle adjustments (float height) required. one thing i would suggest is that the AF graph shown will be delayed some dynos work around this better than others and the operator should be used to this so for carburetted bikes the way of getting a better picture is a through the gear run.
basicly you may be seeing on that graph the fueling graph delayed by as much as 2000 rpm later over the power graph

i.e so where 10000 rpm shows it may be showing the fueling from 8000 rpm so this would put your lean are right in the control of the needle and the reason it goes so rich at the end it could carry on going richer much richer in some cases all for another 2000 rpm not shown on the graph it could carry on dropping down to past 11 afr.

go back to the dyno and just do a through the gear run which will give u a indication of more acuratly of the main jet, then on a single gear run 4th or 5th raise your needle by at least 1mm more if posible and see what happends.

If you are using vfr carbs a 150 main jet is huge blank the main air jet off at the rear of the carbs and run them set to mains of about 126 if using a foam filter or just ditch the filter and try at around 132 main jet. I would try standard needles looking at your graph they have a more constant rate and in most cases acheive straighter fueling lines. Another one is dependant on what carbs are used is bellmouths they affect fueling dramaticly as does ignition. A engine strugling at any rpm point will appear rich on the graph also so you could still be under jetted and the area going richer could be a indication of poor running.. i doubt that is your case i think you just have incorect match of parts.

if your anywhere near the north west i would be happy to take a look at it on my dyno

[Cammo]

The example setup in the rvf hrc manual might be a good starting point (148/152, B needles in 2nd clip position & 0.5mm washer).

I would estimate that your main jet size is pretty much spot on, the a/f reading may be lagging as Chris suggests.

You're using the leanest needle (C), try a richer (B) one.

[venom51]

You need to find someone with a Factory Pro Dyno to tune your bike.

http://www.factorypro.com/

[rallykay]

Some great advises here i must say!

I´ll try some of the above and get back. If someone has something to ad, please do so.

Thanks again for your help. This is a realy great thing with this forum i must say.

Kay

[venom51]

http://www.factorypro.com/tech_tuning_p ... gines.html

[rallykay]

Hello again. Now i have had some more time to think about your answers and of course it raises some more Q:s!

First, the bike and carbs are RVF.

About this delay thing. How do you determine with how much the delay could be?

"The lean are is when you are on the main jet but it goes richer at the end ....... definatly emulsion tube and needle adjustments (float height) required." The emulsion tubes are the ones provided in the HRC kit. Do you mean that the float height should be raised or the needles? Raising the float height would affect the whole curve wouldn´t it?

Some more info from riding the bike. At 8-9Krpm it seems very "eager" but also stumle a little now and then when running at constant throttle. This could also indicate lean running right?

"if your anywhere near the north west i would be happy to take a look at it on my dyno" I live in Sweden but i might take up your offer next spring after a more thourogh engine tuning. I am thinking of using your programable ignintion anyway. Do you do Keihin FCR equipped bikes?

Thanks again for your help.

Kay

[chrisxr]

hi
sweden is along way away yes

when i mentioned the emulsion tube / float relation sometimes it is the case that holes on the emulsion tube differ to stock in there position and amount of drillings on the tube and a float height adjustment is required although this usualy just covers the lower end of things to much float height will case the bike to flood low down but to little can cause a lean area higher up the rev range.

with regards to the delay in the system, this is caused by the length of sniffer tube plus the internal assesment of the data then being put into graph, the delays vary machine to machine, for bikes that a hole in the exhaust purposly for a 02 sensor it is best to always screw dirctly into there that will reduce some of the delay in the system. I have spoke to a manufacturer of a dyno about this and they admit it is a issue that is dificult to overcome but only the dyno operator will be able to let you know how much delay is present through his own experience.

A through the gear run at wide open throttle will give you a good average and point to the main jet figure only in most cases. A single gear run will help you determin the lower circuits of the carburettor.

Yes i have worked on fcr carbs for many bikes fzrs zxrs etc my opinion is that they are only for experienced riders as is the nature of throtle build up but good fuelling results can be acheived far quicker with these as is there design.

If you have some on a V engine would be interesting? I have seen a set of these in a picture made up but have never known of the outcome of such a setup with a nc30 35