The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Bob_Roller on June 13, 2010, 11:54:06 AM
-
I finally got around to replacing the main jets on my '81 R65 from 145's to 138's .
The 138's, I found in the grab bag 'o parts from the project LS I got about a year ago .
In the Bing Carburetor manual, there is a conversion chart to compensate for altitude and temperature differences from how the bike is set for, which is sea level and I think 60 F.
The correction factor for my conditions in summer (1130 ft elevation and 105 F.) work out to a 135 main jet size, don't know if I'll go that small, but I can't seem to find a BMW part number for this size jet .
I'd to see if this size is even available .
Experimenting, trying to get the fuel comsumption back to where it was before the fuel supply here had 10% ethanol added to it .
-
Bob
Motobins stock 135's. Haynes list them for some models of R80.
Having said that at moderate speeds I think fuel consumption is more influenced by float level, idle mixture and the needle/needle jet than by small changes in the main jet.
-
After seeing the various posts about fuel consumption, it looks like the North American version R65LS, came with 138 main jets, from what I have seen from what the riders of these bikes have posted, they seem to get in the range of about 5 mpg more than my bike ever did .
I checked RealOEM, and couldn't find any 135 main jets listed for any R65 or R80 .
Like I said, just experimenting with it, to see if in real life application, it makes any noticeable difference .
Most of my riding, is at 65 mph or higher, only about 2 miles to the nearest expressway, so slow city riding doesn't make up a very high percentage of my average riding .
With the arrival of the 'hot season', I've done the yearly switch to premium grade fuel, 91 octane by our rating system, to prevent detonation due to high air temperatures .
Trying to see if I can squeeze a few more miles out of the slightly more costly fuel .
With the oilhead, I get consistently 20-25 miles more per tank full using premium grade fuel, over regular grade 87 octane fuel .
-
Haynes list the 135 for the 83- 85 R80GS, R80ST and R80RT UK models only so maybe that's why they are not listed in the US.
I suppose the main jets will have an effect on economy at 65 MPH. Even still I bet your not using much more than 1/4 throttle. I found it quite enlightening to mark off 1/4, 1/2, 3/4 and full throttle positions using some masking tape. The throttle action is not linear though which I think means that at an indicated 1/4 throttle it's actually not even that far open. I found that I was using no more than an indicated 1/8 throttle for 50 mph cruising on country lanes. This and my previous experience with other bikes has taught me that pilot circuits can have a significant impact on overall economy as they are still contributing to the mixture up to 1/4 throttle.(http://)
-
I'll try marking the throttle with tape, and see what position the throttle is in for the usual highway speeds .
-
I'll be following this thread with great interest. I'm very disappointed with the mpg of my r65, and gaining 5 to 6 mpg would really be desirable. Do I sound like a broken record?
-
I'll be following this thread with great interest. I'm very disappointed with the mpg of my r65, and gaining 5 to 6 mpg would really be desirable. Do I sound like a broken record?
What sorta mileage are you getting, iman?
Monte
-
I marked the throttle housing and handgrip for the ride home yesterday, at 70 mph I'm at half throttle .
There are some differences in the needle jet and the needle .
The carbs on the '81 R65 have a 2.66 needle jet, and a 241 needle, the LS has a 2.64 needle jet and a 251 needle .
I thought the jet numbers was the area of the opening in square millimeters, don't know how the numbers are arrived at for the needle itself, as they are tapered .
Looking at the manual from Bing, the needle and needle jet are the most controlling factor at about half throttle, just as the graph that Barry has posted .
I'm not so sure now that changing the jets will give me any real change in the usual riding that I do .
-
Looking at Barry,s chart it looks like the main jet isnt an issue unless your hammering it.
Lou
-
After Looking at the graphs, I'm not expecting any serious benefit from the jet change .
The jets didn't cost me anything, like I said just an experiment to see if it would yield any positive results .
-
Monte, I'm getting 40/42mpg. not so bad,but i was expecting more like 45/48, with the occasional 50 mpg, based on pre-purchase research. One of the things that got me back into cycling, after a several year break, was the gas savings. None of my bikes since getting back into it have gotten less then 60. But I didn't enjoy or 'bond' with any of them like I have this bike, so there you go.
-
I thought the jet numbers was the area of the opening in square millimeters, don't know how the numbers are arrived at for the needle itself, as they are tapered .
For needle jets at least I'm fairly sure the jet sizes are the dia in mm as I made up a mandrel to test if mine were worn.
Main jet numbering is different again though because fuel flow vs jet diameter is not a linear relationship. The only jet sizes I know for certain are the 2 fitted to R45's 105 is 0.95mm dia and 123 is 1.05 mm dia so the numbers are not related to dia. I think the numbers represent linear increases in fuel flow so for example using fictitious sizes a 110 jet flows 10% more fuel than a 100.
BTW how fast could you go at 1/4 throttle.
-
I'm not sure what speed I would be at for 1/4th throttle, next time I get out I'll check it
-
... I'm getting 40/42mpg. not so bad,but i was expecting more like 45/48, with the occasional 50 mpg...
At 40+ mpg, you're pretty durn good. Guessing a long highway run at steady revs around 65 mph may raise your fuel average. It's all in the wrist, iman! My wrist is too twitchy to get more than the occasional 40.
Monte
-
yeah, I'm slowly learning to let it go. with that said, I'm really interested to see what Bob and Barry work out. If I could get 5 more mpg, I'd shut up (about mpg's, anyway)
-
This and my previous experience with other bikes has taught me that pilot circuits can have a significant impact on overall economy as they are still contributing to the mixture up to 1/4 throttle.
Barry,
The graph you posted is fascinating and very informative. It's a great overall depiction of the circuits. Where did you find this? Did you create this yourself? I didn't see this in the Bing Manual.
-
Where did you find this?
Mike
I honestly can't remember where. It's just something I saved - certainly didn't do it myself. I'll have a look when I get home from work.
There are a few of these graphs around and not all are applicable to CV type carbs. If the graph has a line for slide cutaway it usually means it's applicable to slide type carbs rather than CV's. That's a good one though.
-
The Bing manual has a much more simplified grahpic on page 11 at the upper left corner of the page, if anyone has a copy of it .
-
Barry,
It's an awful comprehensive graph. Very helpful as an aid if accurate. I question the height of the curve for the metering rod but I just wonder why we haven't seen something like this before. It was my understanding 1 notch on the metering rod equals about 2.5 jet sizes. Do you mind if I share this with some Airhead friends to get their opinions? Anyone else out there have any comments on the graph?
Bob I noticed the graph in the manual. The manual has several graphs (pg.3, 11, 15) and would be nice to have a composite like Barry posted to see overlapping functions.
-
Do you mind if I share this with some Airhead friends to get their opinions? Anyone else out there have any comments on the graph?
Mike, Sure it would be good to hear what they think. Couldn't find the original source but I am sure it represent a CV carb though probably not a Bing. That shouldn't matter as they all work the same in principle. The various graphs and diagrams around are very similar and who knows how accurate they are. For me they are an insight in to how the carb works.
Here's my take on each of the curves:-
Pilot screw has a diminishing effect from idle but still some small effect past 1/4 throttle - I agree
Pilot jet flowing fuel from idle up past 1/8 throttle. This is the most interesting curve because it's usually missing from other graphs and diagrams. - what this means is that the transfer ports which are not controlled by the mixture screw are still flowing fuel upto and past 1/8 throttle. I agree but not sure about the shape of the curve I would expect it to turn down again.
Needle diameter - Before the tapered part of the needle is pulled out of the jet this is contributing fuel flow upto 1/4 throttle. I agree in principle and for me this equates to around 3000 RPM. Not sure about the scale of the curve though. I think you can only compare the height of this curve with the other jets that are contributing at 1/4 throttle and not with say the needle taper at 1/2 throttle.
Needle clip position - This one is confusing. I would have said that needle clip position simply moves the needle taper curve from left to right on the graph and to some exent up and down the graph because it determines at what throttle opening the needle taper comes into effect.
Main jet - Agree in principle but I would expect to see the curve extended down at least to 1/2 throttle and maybe 1/4 throttle even though it's effect down there would be very small.(http://)
-
Barry,
Your graph is getting a lot of attention here in San Diego with very positive reviews.
-
Mike,
I look forward to hearing what they have to say.
-
I've sent it out to a handful of close airhead friends here. They all initially ask the same question about the source. But I have a feeling it's finding it's way into a lot of notebooks because of everyones high impressions of the comprehensive nature of the chart. I've tried some shots Googling to find it in some corner of cyberspace with no luck. I may send it to Jan, Stoner, and others to get some expert impressions. Sorry to move away from the original Subject line, no disrespect intended.
-
BTW how fast could you go at 1/4 throttle.
1/4th throttle is around 38 mph
-
1/4th throttle is around 38 mph
Bob,
I was so intrigued with your result I went out and marked my throttle up again taking care to allow for the initial slack. Ive just come back from a short test ride. What I did was to hold a throttle setting and then wait to see how fast the bike would go before I ran out of road. Here's what I got :-
Holding 1/8 throttle I can accelerate up a moderately steep hill to 40mph. On the flat this increases to 50mph.
Holding 1/4 throttle I can accelerate up a slight gradient to 60mph and on the flat this increased to 65mph. The Road ran out before I could go any faster.
These results are much the same as I got before and they are the reason why I'm a bit obsessed with the notion that pilot circuits on the carbs make a big contribution to MPG because I rarely seem to be using more than 1/4 throttle.
(http://)
-
I rechecked the markings on the throttle housing and hand grip last night .
This morning I rechecked my findings, 43 mph for 1/4 throttle, and 73 mph for 1/2 throttle .
The surface streets around here have a 45 mph speed limit, and a stop light every mile, so the speed may well be higher for 1/4 throttle, have to wait until I get out on a deserted back road with no traffic to see for sure if it does change .
-
According to this article, we here in the US can expect to get lower fuel mileage if and when this goes into effect .
http://news.yahoo.com/s/ap/20100618/ap_on_bi_ge/us_epa_ethanol
-
Interesting, I suppose it can be put down to different engine , different carbs, maybe even different throttle cam.
The only other similar reference I can remember seeing is this from a guy called Mike Fishwick who was talking about tuning his R100 carbs
"Set up like this quarter throttle will give (with an RS fairing) 90 mph and 100 mph at half throttle"
Sounds incredible that you can go that fast on 1/4 throttle but he was Technical Officer of the BMW club and not given to exaggeration.
-
According to this article, we here in the US can expect to get lower fuel mileage if and when this goes into effect .
Bob, the link didn't work for me but I assume it's about the proposed increase from 10% to 15% of ethanol. That's bad news. I should be grateful we are only on 5% ethanol blend in the UK.
-
Interesting, I suppose it can be put down to different engine , different carbs, maybe even different throttle cam.
The only other similar reference I can remember seeing is this from a guy called Mike Fishwick who was talking about tuning his R100 carbs
"Set up like this quarter throttle will give (with an RS fairing) 90 mph and 100 mph at half throttle"
Sounds incredible that you can go that fast on 1/4 throttle but he was Technical Officer of the BMW club and not given to exaggeration.
I wouldn't doubt his results, the R100 bikes had different final drive ratios, I think it was set up for long distance and high speed, R100's get about the same fuel mileage as the R65 .
I'm sure an RT fairing would gain you some extra miles due to streamlining the bike, lets face it, and unfaired motorcycle with a rider on it, isn't the most efficient shape, if I remember correctly an unfaired bike with rider had a coefficient of drag of a bit less than a flat plate .
The article was about the possibility of having 15% ethanol in the fuel supply in less than a year .
Owners manuals of most vehicles in the US state that fuel with ethanol content of more than 10% should not be used .
What's the final drive ratio on your bike, 3.89 ?
My R65 has a 3.56 ratio .
-
What's the final drive ratio on your bike, 3.89 ?
Yes its 3.89
I would think the RS fairing helped. I sometimes feel like a flat plate at high speed and that's with the low Euro bars.
-
Filled up the fuel tank this morning, first time since installing the 138 jets .
5.3 gallons US, 227 miles .
Works out to be about 42.8 miles per gallon .
Looks like I may have gotten a bit better fuel consumption with the smaller main jets .
But this is only one tank, to be continued...............
-
Bob,
Any noticeable change in general performance, acceleration, responsiveness with the smaller jets?
-
No noticeable change in the performance or general characteristics with the way the engine is running .