This July I got a 92 R100R that needed lots of help. I fixed all the electrics and started on the mechanicals after lots of work she is running good, or so I thought. I have a friend with a dyno and strapped it down to get a reading on my A/F ratio. It turned out to be 10.5:1 though the entire rev range way to FAT! I did rebuild the carbs with a Bing kit, all the jets are the correct size and I started at the base settings for the carbs. The starting circuit is built correct, on the proper sides and are adjusted to go fully off. The floats are in good nick and correct height. I could lean it back some with the mixture screw but not enough. I checked and adjusted the valves and the carbs sync well at idle and 3500 RPM and she is getting about 38 MPG. I have heard that the jet needle can wear and cause a rich condition but would it do it through the entire range? Or should it only go rich 1/2 throttle and more with bad needles? The plugs look a bit rich evenly on both sides.
Thanks for your time and help.
Kinda over my head, but I managed to find an older post that touched on the subject. Not sure it's much help.
Did you replace the needle jets when to rebuilt the carbs? The needle jets do wear, the jet needles wear very slowly.
[QUOTE=47512;896943]Did you replace the needle jets when to rebuilt the carbs? The needle jets do wear, the jet needles wear very slowly.[/QUOTE]
I did not replace any of the jets or needles I just put them through the wife's sonic cleaner with DI water. But would those jets affect the entire rev range?
What notch did you set the needle in and did you count from top or bottom? (They're numbered top notch to bottom)
Did you check what size main jet you have? (It has a number on the side). Is it the stock one, or bigger?
[email]Airheads@micapeak.com[/email] is a great mail list that could probably help some.
[QUOTE=YYZED;896944]I did not replace any of the jets or needles I just put them through the wife's sonic cleaner with DI water. But would those jets affect the entire rev range?[/QUOTE]
According to the Bing book, the needle and its jet are effective from 15 to 80% of throttle. There is overlap with the idle jet on the low end and the main jet on the top end.
I wonder if someone has (or can) relate with some certainty where these "transition" places are (by rpm's or % of full throttle) - from idle to needle, and then the transition from needle to main jet.
The other thing I would like to know would be the exact amount of taper on the jet needle per length of linear travel. With that knowledge, one could calculate the amount of size difference (diameter of needle) at one point, and then figure out the diameter of the needle at another point a certain distance away (like from one "notch" to the next "notch."
Also, is the amount of taper the same throughout the full length of the jet needle? There could be two or three different tapers in that length, but I doubt it.
If I had a brand new jet needle, I could put it on a comparitor and measure it.
It would also be nice to know the exact dimensions of the passageways in both the idle jet, the needle jet, and then the main jet.
I am also wanting to know just how much "wear" (size-wise) on either the needle jet, or the jet needle( or both) there needs to be to actually affect the running of the motorcycle.
Bing spends 2-3 pages in their book discussing the needle and jets. They also publish the % overlap...most likely for a standard configuration...that would be all over the map for different carbs, different states of wear I suspect. The main jet numbers are essentially the diameter of the jet in mm. The information you're looking for might be there. :dunno
Magazine articles from the late '70s tried to describe how the CV carb worked.
Well Clymer is worthless as far as the 92 R100r settings, but if I use the 1988-1989 it shows the following:
Right hand carb 64/32/358
Left hand carb 64/32/357
Do those match what's on your bike? If so it shows the following:
Main jet : 135
Needle jet: 2.66
Needle jet # 46-251
Needle clip position from top: 3rd
Idle jet # 45
I'll try to look it up in my bing book when I'm back out in shop. (Sign up for airheads list and you'll get great assistance. :) )
Those are the numbers from the Bing book for 357/358 carbs. It also suggests the idle mixture initial setting as 0.5 turns out.
I checked and adjusted the valves and the carbs sync well at idle and 3500 RPM and she is getting about 38 MPG. [/QUOTE]
Everything else aside, from what I've read and experienced on my 88 R100 RT, high 30's fuel economy is typical for the mid 80's bikes onward. Very few riders report MPG above 40 for the later bikes. These later bikes to do not get the same fuel economy as their earlier brethren. So, if everything's OK, just ride and enjoy it. Anyway, that's my take on it.
I've repaired and rebuilt more than I can remember motorcycle carbs over the years. Other than tired diaphragms and leaking throttle shafts on butterfly carburetors needle jets make a big difference.
Needle jets are made of brass, needles are made of a harder material, mostly stainless but not always. Vacuum sucks them forward so they tend to rub on the forward inside of the jet. Wear there can be just a few 10ths of a MM, with a diameter that small it doesn't take much wear to make them run alittle rich.
On a 20 year old motorcycle there's going to be some wear.
Also the throttle shafts tend to leak air on older Bings so people set the idle mixture alittle richer to compensate. They run ok, they just use alittle more fuel.
This weekend I dropped the needle one notch (was on 3 now it's on 2) and it felt much better and my milage went to 39 MPG at elevated highway speeds in heavy winds. So with 55k on the clock I'll order new needles and jet and maybe 2 sets of smaller main jets. I just did not think that the needles made that much of a difference I would have chased floats or the starting circuit all day long.
When I rebuilt the carbs I did check with the Bing book and all parts are the correct # and I set them to the starting settings. I guess if something is going to wear out I'm glad it went rich rather than lean like my RD did, that did not end well.
Replace the needle jets, and the needles if you wish. I wouldn't mess with the main jets until your shure it needs more fuel at wide open throttle.
Do one thing at a time to make shure that corrects the issue. The needle jets are a good start.
You might make shure the floats float. Ethanol in gasoline has been known to wreck plastic floats.
I think there are some odd data points here.
I have only ever seen very high 30's mpg (miles per US gallon) on my 23,000 mile 1993 R100R on long lightly-loaded lazy trips. Similar story with my 40,000-mile 1993 R100RT. Typically running errands I see 32 mpg, and short runs around 35 mpg.
On this basis, and depending upon your riding style and journey type, your 39 mpg and the reported A/F ratio do not seem to stack up.
If the plugs are not showing an overly rich mixture, I'd just get on and ride.