What speed, dyno load and gear were you running when you observed this rich condition?
Also, after riding, do the finger up the exhaust test. Let it cool, then stick your fingers in there and run them along the sides. If your fingers are full of soot (fully black or chunky), you are running very rich. Lightly coated , skin very visible, is just right and yields good fuel economy. L/R tips should give the same reading.
39 mpg seems reasonable to me. I get 45-49 on my R80RT, depending on what I am doing.
Through this post, I was emailed privately and introduced to a person whom I think is a Bing expert, but not personally on this site. He gave me lots of valuable date about needle jet and jet needle.
But the most valuable to me, however, was his advice to look at throttle position when riding. Most of us rarely ever go over 1/2 throttle. I ride usually pretty steadily around 60-70 MPH and at that speed, my throttle position is only about 1/3 of the way. His point was that the high speed jet (Main jet) has very little, if any, influence on mixture. Rarely, if ever, does a person go "full throttle". Most people's riding is done when MOST of the mixture is really done by Needle jet, and jet needle. However, he also pointed out that the idle jet influences virtually all jet ranges as the idle inlet to the venturi is always sending gas to the engine. Hence. he also stated that most people adjust the idle mixture screw too rich (advice I have seen suggested right here on the web site!) and therefore, coupled with needle jet/jet needle being somewhat worn will produce a too rich condition all through the idle to mid-range position.
I am not an expert, by any means, but I went out, and warmed up my bike (took for a 5 to 10 mile ride) and took along a screwdriver. I pulled over, and then set the idle mixture, but this time, I didn't back out screw to "safely" get it richer, I got carbs to their best idle running. This one action affected my engine performance all the way up to 5,000 rpms (about 1/3 to 1/2 throttle position). Ran much smoother and transition from maintaining a constant speed (at virtually any speed) to acceleration was much smoother!
Just my 2 cents
[QUOTE=jimmylee;899204]Ran much smoother and transition from maintaining a constant speed (at virtually any speed) to acceleration was much smoother![/QUOTE]
I think that's called the placebo effect! :stick
Seriously, though, I made note of the throttle while running this morning on the freeway at a steady speed...about 65-70 at 5th gear at 4K RPMs...slightly wind-aided but not much. I was probably at about 1/4 to 1/3 throttle. Probably makes sense because the faster you go, the more the drag goes up (by the square of the speed) and it's going to take more and more throttle to get that next 5 mph.
[QUOTE=20774;899242]I think that's called the placebo effect! :stick
Seriously, though, I made note of the throttle while running this morning on the freeway at a steady speed...about 65-70 at 5th gear at 4K RPMs...slightly wind-aided but not much. I was probably at about 1/4 to 1/3 throttle. Probably makes sense because the faster you go, the more the drag goes up (by the square of the speed) and it's going to take more and more throttle to get that next 5 mph.[/QUOTE]
I agree about your assessment about the throttle - has to go up at a greater amount than speed would.
Also, as I was thinking about it, technically, throttle position does not equal speed as per your observation. If one is going uphill (or against wind) at a steady speed (let's say 50 mph) he would have to have greater throttle than if going the exact same speed going downhill (or with the wind at his back). Just an observation that I am sure you already know!!
To be honest, I was skeptical when told. However I tried to be "unbiased" and it really did seem better. My next move when I can get the money together is to purchase new needle jets and jet needles along with appropriate "O"" rings and then diaphragms (although my current ones look good) and gaskets.
As you are aware by now, I am the most unbiased, non-opinionated person you know!! hehehe
Even with those variances, as you pointed out, we're running on the "needle" pretty much all the time. According to the Bing book, the main jet doesn't come into play until around 60% of throttle.
Another issue too.
The throttle position on these CV carbs also could vary based upon air flow (thus creating vacuum above the slide). If, let's say, the throttle plate position could be required to be more open in the event that the cylinder had leaks, lower compression, etc. in order to create the same slide position as on the other carb that may be connected to a cylinder with better compression, no leaks, etc. However this variance supposedly would be compensated for when one adjusts the cables to achieve both sides to have the same operating pressure - thus, theoretically making both cylinders contributing the same amount of "punch" to the stroke.
I think we should just limit the discussion to a bike in reasonably good running condition...ie, getting the nominally correct gas mileage...that's typically my judgement for running condition. Sure, bad spark plugs, weak ignition, imbalanced carbs, low pressure in the tires, on and on...they're going to contribute to more throttle to get down the road. No way can you quantify how each contributes to throttle input.