The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Andrewsteward on August 17, 2014, 02:43:33 AM
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Hi all. Just for reference, I was wondering what would be 'normal' fuel consumption for an R65?
I am only getting around 200 km per tank. This is based on 50/50 city/highway riding.
Seems a bit light on to me.
Any thoughts?
thanks
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That seems diabolical at something like 9L/100km or the very low 30's MPG (IMP). I can easily double that. But how much do you mean by a tank ? A tank is supposed to be 22 litres but it's near impossible to get more than 18 litres in unless you run it bone dry. I based my figures above on 18 Litres. What ever the figure is it's still going to represent poor fuel consumption so something is wrong.
Seems very likely you have some problem with the carbs like worn needle jets or chokes that are not fully off. In which case to set a base line and monitor any improvements you make it would be good idea to take accurate records of the consumption in units we can make comparisons with.
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As Barry has said, the most likely issue is with the carbs .
If you are not the original owner, there could be a previous owner ' modification ' to the main jet sizes, needle position on the slides as well .
Do you fill the fuel tank to the same level each time, I use the bottom of the filler neck as my fill point .
Other possibility, is, how accurate is the odometer ??
These bikes are known for their speedometer and odometer issues .
Before the addition of ethanol to the fuel supply here, I would average about 19 km / L, around 370 km to reserve, 45 mpg, 225 miles to reserve .
With 10 % ethanol, I average 17 km / L around 330 km to reserve, 40 mpg, 200 miles to reserve .
Both carbs were rebuilt about 11,000 miles, 18,000 km ago .
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Cleaning and rebuilding the carbs to the specs BMW put from factory pays for itself soon.
I can ride around 360~ 370 km before switching to reserve. A lot of town and a few highway (I use the bike for the work commuting. )
So definitely you can improve the figure !
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Thanks guys, yes looking pretty grim. 200k is to the reserve give or take 10 or is pretty damn shite given what you have all just posted.
I have adjusted the needle position, only on one side as in one of my previous posts, I had a flat spot at 1/4 throttle.
I found that the left side as in a richer position (higher) and had very sooty plug etc.
So I evened them up, ( made left same as right ) and it seems to run like a dream and both plugs have good colouring.
I have adjusted the choke cables to ensure free play as that was also a problem on the left side prior.
As I am not the original owner, and actually only had the bike 3 months, it sounds like I should go down the path of a set of needles and main jets at least to standardize.
Would it be worth dropping the needle position down one more notch first to try?
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If you post the carb numbers, we can give you what the setting was from the factory, as well as the main jet size, etc ....., the numbers are on a vertical flange at the front of the carbs .
The numbers should look something like this : 32/64/325, this would be a left carb, 32/64/326 would be a right carb .
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ok L/H/S 64/32/307
R/H/S 64/32/308
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Bear in mind that moving the needle one position is a huge change especially at low needle lifts where it produces a 40 % change in jet area at zero lift falling to 5% by full lift.
One needle position is generally considered to be approximately equivalent to a 3 size change in needle jet. A one size change in needle jet changes jet area by 10% at zero lift falling to 2% at full lift.
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Andrew,
Do not tweak needle position ! Start first by overhauling the two carbs. First, clean them with brake/carb cleaner (be sure to unclog all the tiny passages around the butterfly valve, and all the other passages.
Then put new brass on it : needle jet, main jet, idle jet and new needle at stock position. A new set of diaphragms and new O-rings will finish the job.
The bike should run from fine to excellent and the mileage should be way better.
Then you can divert from base settings if the response is not as desired nor fine enough...
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Main jet size 145, needle clip position 4 ( this is counted as the very top position being 1 ), idle jet 45 .
Just curious, what elevation are you at, there is a correction chart for elevation and temperature, but I'm guessing that this is not a factor in this, they are not large corrections, unless you are at high elevation, or high temps .
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Spec I've got for those carbs is 148/2.64/4th/45.
It's very rare for Bings to use position 4 on the needle even with the smaller 2.64 needle jets. Sounds very rich to me and I notice the following model year the needle was dropped to position 3 while retaining the 2.64's.
I'd be tempted to try them in position 3 straight off even before replacing the needle jets. personally I wouldn't bother buying new Mains or idle jets unless there were obvious signs of damage as they don't wear.
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thanks all, so just to clarify before I start on this.
Needle position 1 is the needle at the longest possible length? Top position as in top Notch?
and it should be at 3 or 4?
and by moving the needle up in the piston, I feel its getting a richer mixture. Is that correct?
I cant remember where its at but will pull down on weekend.
Im in Melbourne, so sea level, chilly but not cold.
thanks again all, youve been wonderful [smiley=bmw_smiley.gif]
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Thanks all, so just to clarify before I start on this.
Needle position 1 is the needle at the longest possible length? Top position as in top Notch?
That's correct 1 is leanest and 4 is richest. Our needles are not quite like the diagram below but it serves the purpose. If you want to check which position you are in compare the exposed length to this table. Don't worry if your measurements are not exact. There is approx. 1.8mm between positions so the which one you are in should be obvious.
1 42.37
2 40.57
3 38.79
4 37.10
and it should be at 3 or 4?
The original spec says 4 but I'd also try 3. The reason I suggested trying 3 straight off before doing anything else is it might compensate for worn needle jets while you get around to replacing them. No way position 2 or 1 would work with 2.64 needle jets unless they were very badly worn.
and by moving the needle up in the piston, I feel its getting a richer mixture. Is that correct?
Yes
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Barry,
Excellent advice (as always), the carb rebuild/refurb/whatever is on the horizon for me, so I have noted & filed away for reference.
No doubt I shall be seeking advice at some point soon...
Thanks
Chris
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So here's a grim thought: not that long ago I was getting around US 33 mpg.. I ended up getting the transmission rebuilt and now I'm up to 41+ mpg.
Either the transmission rebuild or the new rear shock made the difference.
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That's an interesting one and in percentage terms a very big difference. The gear box absorbs power at the best of times. Failing bearings and resultant misalignment would absorb even more than usual and use more fuel.
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So here's a grim thought: not that long ago I was getting around US 33 mpg.. I ended up getting the transmission rebuilt and now I'm up to 41+ mpg.
Either the transmission rebuild or the new rear shock made the difference.
mmm lests note hope for a tranny re-build.
just pulling carbs apart now
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Ok first report-nothing much to report though.
Needles position 3 though left side circlip a little dis-logged but only about 0.5mm difference.
Main jet 145. Couldn't tell what the needles were. No markings.
Still running well, havnt run a full tank yet so cant tell about consumption.
plug colours are perfect.
Compression is at 110/side so yes getting tired, so maybe adding to the consumption problem.
Just wondering if the clutch maybe slipping? Its not apparent but just a thought.
How many revs should it be at 80k or 50mph?
I do have a noise when the clutch is engaged. I might try and post it
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....Couldn't tell what the needles were. No markings.
The needle should be a 46-241 which is used in the majority of Bing carbs on Airheads. I suppose it's possible someone substituted the wrong needle but it's not something you hear about often if ever. I have some reasonably accurate dimensions for a 46-241 needle if you want to measure yours. They are easy to measure as our needles are a simple straight tapered cone. That's not true of all Bing needles in other applications though.
Needle diameter 2.45mm
length of tapered section 23mm
Minimum diameter of taper 1.2mm
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Thanks Barry, I will check on the weekend.
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I just seem to be lucky then, my motocycle gives me 20km/l and that is combined cycle, hi way and town driving.
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OK multiply 20km/l by 2.824809363 and we get 56.5 MPG (IMP) or 47 MPG (US).
Not bad at all.