The International CBX Owners Association

Hi, I have a mentioned discussion ongoing in cbxworld forum.
http://www.cbxworld.com/modules.php?nam ... pic&t=9313

Hope to get some opinion about air/fuel ratio figures and possible tuning
suggestions.
Like I wrote I was quite staggered that engine is running so much rich.

piit, I'm afraid that site requires a member "sign in" to open, could you copy & paste or present the question here. We would be more than glad to advise....

Ok, thanks for the informations. I will do the copy/paste actions asap.

ok, let´s try again. Whole topic copied here also.
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Some graphs from today.
Bike is running with stock airbox/filter, jets, needles not shimmed.
Modifications done as mufflers, dyna-s ignition and dyna coils. Pilot screw opened 2 turns.
After I removed original 422 mufflers I felt a little torque degreasing between
approx. 5000-6000rpm and actually dyno proves it now. At the same time I felt that
engine took higher rpms faster.

Bike is running currently rich.
I want to lean mixture now from 4500-5000rpm till end.
I want to do one modification at time and in my opinion I shoud decrease secondary jet.
What is the rpm area handled by secondary main and primary main?
Also have you check the air/fuel ratio normally when re-jetting carbs. I can see that trend is
to put bigger jets and in my case I need to put a lot smaller jets.

EDIT: Graphs are from rear tyre.

Please find the dyno session pics from the link below:
1st pic: CBX in dyno
2nd pic: 1st run from right side
3rd pic: 2nd run from right side and 3rd run from left side combined in same picture. Red one from left side and blue one from right side

http://kuvablogi.com/blog/14304/2/

Additionally I want to mention now that the landba sensor was located at the end of the pipes. So the figures are more lean than would be if measured just after the collector point in pipe. Also the lower rpms A/F ratio cannot be analyzed for the same reason, but gives some "trend" for A/F ratio anyway. During the winter pipes will get the places for the landba sensor after the 3into1 collector points. Then the A/F ration can be carefully analyzed from the idle to near 10 000rpm.

What is interesting piit is the A/F ratio between the left & the right side at about 5000 rpm, there "seems" to be some interaction there, which is very strange... I need to give that some more thought...
As previously discussed, I think it important to have the float level corrected & the sensor measuring at the collector.

Looks to be a strong running CBX though....

OK, I've been thinking....

The F/A ratios are being read by an exhaust gas analyser ( lambda sensor) both left & right side.
As 3 cylinders share each exhaust system, I would look at individual spark plug readings on each cylinder, as your results are being averaged. It could be that one or more cylinders/carbs are biasing the averaged reading..Also, any small air leaks on the induction &/or the exhaust side could be leaning out the left side...

I seem to remember, Larry, when we played with your ex gas analyzer in Maggie Valley, that the Xes we checked were ALL slightly leaner on the left side

Hmmm, Your memory is better than mine Mike.... On recollection, I think you are right...

Thanks guys for the comments! It is for sure now that one reason why my engine is running rich is too high float levels. Less that 15.5mm because I have measured from end of the floats not from midpoint as instructed in Honda manual (thanks alimey4u2 to clear this out in other topic!).
The spark plugs show that 1&6 are the leanest and richen to middle, but colour does not show bad rich. I have checked the air leaks with pilot start spray, no leaks with inlet air. Exhaust is leak-proof.
Anyway I will adjust my carbs again to 15.5mm as instructed in Honda manual during my valve seals changing. Also I will weld the sensor places close to collector points on both pipes.
I will share the new dyno graphs via this topic hopefully soon but in spring at the latest.
Most probably I will not get any or only minor improvements with leaner A/F ration, but let´s see.

Stolen from Wikipedia..

Lean mixtures produce hotter combustion gases than does a stoichiometric mixture, so much so that pistons can melt as a result. Rich mixtures produces cooler combustion gases than does a stoichiometric mixture, primarily due to the excessive amount of carbon which oxidises to form carbon monoxide, rather than carbon dioxide. The chemical reaction oxidizing carbon to form carbon monoxide releases significantly less heat than the similar reaction to form carbon dioxide. (Carbon monoxide retains significant potential chemical energy. It is itself a fuel whereas carbon dioxide is not.) Lean mixtures, when consumed in an internal combustion engine, produce less power than does the stoichiometric mixture. Similarly, rich mixtures return poorer fuel efficiency than the stoichiometric mixture. (The mixture for the best fuel efficiency is slightly different from the stoichiometric mixture.)

A very interesting thread piit, please keep us updated...

So, it´s better to run rich as the honda engineers decided it. You are right this is interesting Will be nice to see the dyno figures after I have adjusted the fuel levels correctly.

Due to US emission standards rapidly dumped on motor vehicle manufacturers of that day, their knee jerk response was to lean out their engines in the control (measured) rev range. The Yamaha Virago was so leaned out that it had a habit of spitting its carb bodies off the engine...The CBX was an easier engine to ratify due to the smaller cylinders ( efficient combustion chamber space ) for its capacity & dual burn sparking.

I think we all await the latest Dyno runs with anticipation piit....

Story continues. Here is the copy paste from that innominate forum

I was planning to go dyno a bit earlier but time is running so fast.
Here are the latest graphs (from today). Same dyno and place. Both hp and Nm increased, now approx. 95hp/78Nm.
AF ratio is now quite good and going right direction. Only beginning of rpm too lean and might be difficult to adjust
without affecting on the higher rpm area?!
http://kuvablogi.com/blog/14304/4/

After you have opened the picture you should see the picture description, but blue is before and red is after the modifications.

Impressive numbers piit. Lean on/off idle will be difficult to accurately calibrate as it's tough to get all 6 voices singing the same finite tune. However there are greater minds than mine on the subject & hopefully they'll assist further..