More mid range for R100?

Discussion in 'Airheads' started by Nortryder, Sep 8, 2010.

  1. Ron In Buffalo

    Ron In Buffalo Adventurer

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    I agree w/ this guy I have a 1977 r100/7 w/ 32 mm carbs and smaller valves and give riders on the rs/s/rt fits up to 100 mph. Then after that point their hp wins. Bit if you are after more torque less id more. Ron
    #21
  2. supershaft

    supershaft because I can

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    I really try to avoid mileage stories even with some of my good friends. Same goes for tire wear. Man! Think of all the pipes that have been packed and lit and journal entries made on those topics! Usually, I raise my arm and point as far away as I can and advise that the Star Trek convention is THAT way! :rofl Still, I don't remember ANY of our customers reporting anything like that back then. Some low to mid forties and mostly mid/upper thirties are the stories we heard "back when gas was good".

    Besides alcohol, what has changed in gas that effects mileage? I have been riding my own beemers for 30 years now and I have noticed no change in mileage except for the predictable results of 10% alcohol added.
    #22
  3. bmwrench

    bmwrench Long timer

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    Lower Octane! We used to be able to run 9.5:1 or better, with full advance on pump gas.

    With the introduction of ethanol, I find I am forced to re-jet amost every bike I work on. We know that ain't going to improve mileage.
    #23
  4. supershaft

    supershaft because I can

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    Funny, I remember ALL kinds of our customers installing thick base gaskets and dual plugging to reduce pinging "back when gas was good".

    OK, higher CR will increase mileage but NONE of our touring customers were raising compression. They were LOWERING it for pinging! If it ain't pinging, higher octane won't help anything. 83 octane has got the same amount of calories in it that 110 octane has.

    Why are you forced to re-jet with the introduction of ethanol? I never have. I have never needed to. Neither has anyone else that I know till now. Once a little off idle, the stock jetting is PLENTY rich enough to coupe with 10% ethanol. ESPECIALLY the earlier airheads! I jetted my R100 down to 130 mains for MORE POWER on 100 octane race gas and it runs just fine on 87 octane with 10% ethanol. That is until the ambient temp gets high, then it needs 91 octane!
    #24
  5. Airhead Wrangler

    Airhead Wrangler Long timer

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    I actually get slightly better mileage on mid grade than regular at 8.2:1. Explain that. No, this was not a single tank freak occurence. A guy I was riding with told me he got slightly better mileage running mid grade in his thumper, so I called bullshit. I alternated between regular and mid grade for 3000 miles in Argentina and sure enough, I consistently got better mileage on the mid grade. There are various degrees of preignition. It can be much more subtle than audible pinging. Though smaller amounts of preignition won't necessarily damage your engine, they won't help your gas mileage either.
    #25
  6. supershaft

    supershaft because I can

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    I think most call pinging detonation since it is usually post ignition but I agree with you that there is pre-pinging pinging. I don't know what the correct term for it is.

    Preignition is when something sets the mixture off before the spark plug does or, in the cause of ignition wire cross fire, before the spark plug is SUPPOSE to spark.

    I have noticed pre-pinging pinging through better performance of higher octane gas than compared to lower octane gas even though there was no audible pinging on the lower octane. That's why I run 91 octane in my R100 most of the time although, for the most part, when I have noticed a difference it has been on two strokes. I don't know if I have ever noticed a performance difference on my R100 between 87 and 91 octane but I have between 91 and 100 although at least a big part of that is that the 100 octane doesn't have 10% ethanol in it.

    I have never noticed any difference in my mileage between burning lower and higher octane. If there is, it ain't much. I have noticed differences in mileage from differently loaded bikes, jetting, ignition timing, elevation, headwinds, tailwinds, and, by far to the largest degree, how I ride. How I ride can change my mileage by 20mpg and it would probably be by an even larger margin IF I could slow down a bit more. Basically, my riding and headwinds vary too much to analyze my mileage down to a nat's ass. I think that holds for most of us.
    #26
  7. caponerd

    caponerd Kickstart Enthusiast

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    Shaft, you're really taking an unpopular stand here.

    Personally, I tend to agree with you about the fuel milage thing though.
    When I first got my 1982 R100RT, everyone told me to expect 50 mpg with it.

    I had the bike gone through by Steve Prokop in Oregon right after I bought it (turned a $2500 bike that I bought for $3000 into a $5500 bike that was only worth $3000!)
    It's never returned much better than 40 mpg, and that didn't become commonplace until I installed an RS fairing for summer riding. I don't baby the bike, and I think 75 mph is a fair average speed when I'm on the road with it. If anyone claims 55 mpg (or maybe even 50) for one of these, I'd have to assume they really aren't tracking their milage very well.
    I got in the habit many years ago of recording all fuel purchases/odometer readings because I was doing a lot of driving for work and I needed to keep good records. This became enough of a habit that I keep a record of fuel purchases for all my motorcycles.
    It makes a huge difference to have an ongoing record. Just noting odometer reading and fuel amounts isn't sufficient because no matter how careful you are, the tank's not always going to be filled exactly the same, and the readouts on many gas pumps are often inconsistent, in spite of DOT rules and certification of pumps.
    #27
  8. supershaft

    supershaft because I can

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    Boy Howdy caponerd! It's never stopped me before especially when I think the alternative view needs saying! Thanks for your input. It makes 110% sense to me. I know that our position is out there big time but it is rarely on the web for some reason. Maybe the internet is a little too close to that Star Trek convention I joke about and point to to fellow pipe smoking beemer riders like ourselves! Ask just about anyone that doesn't ride beemers and they will tell you that just setting on one will get you half way to that convention without even moving an inch! :rofl
    #28
  9. Beemerboff

    Beemerboff Long timer

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    Nobody ever mentions that unleaded gas burns faster than the leaded that was around when BMW set the advance figures 40 years ago.

    I do my tuning , including ignition timing, on the road, up a decent steep hill.
    I ended up with 26/27 degrees advance on my twin plugged 1000 cc R80 G/S, 2/3 degrees less than most self styled experts recommend.
    It has factory low comp pistons in a unmodified head. That got me up the hill around 5/6 KPH slower than my buddies 86 Suzuki GSXR 750R.
    And 50 KPH slower than his Honda SP2.

    Other mods, like removing the snorkels from the air box which are supposed to kill midrange actually improved my speed up the hill.

    Like Supershaft I find a lot of what is written on airheads is just bunkum, which has gone unchallenged for years.

    Pity there is nothing authoritative out there, even getting someone who knows the optimum squish clearance is almost impossible, and that is a basic and essential figure to have.
    #29
  10. supershaft

    supershaft because I can

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    Leaded really doesn't burn any faster than unleaded. That is a common but oversimplified way to look at it. Lead was added to gasoline in the very late twenties for one reason and that one reason is almost all it did. That reason was to reduce pinging. That is all octane rating is. The comparative ability of gasoline to resist pinging as tested by listening to it ping or not ping in a test engine. High and low octane's flame front burn rate from the spark plug is the same regardless of whether it has lead in it. The difference is in the mix getting squeezed by compression AND the flame front that is IN FRONT OF THE FLAME FRONT. THAT is where higher octane gas burns slower and even that is misleading. High and low octane gas burn at the same rate as the flame front is compressing it and consuming it. That is until the lower octane gas in front of the flame front explodes instead of burning. That is pinging. Higher octane gas doesn't burn slower, it explodes less. Other than that trait, there is virtually no difference between high and low octane rated gasoline as far as the energy involved and the "burn rate" is concerned. That's my $.02 on that subject.

    I thought I would add that those facts are why you can see evidence of pinging by reading piston tops. The very outside edge of the piston top all the way around will will suffer from the carbon getting chewed up versus a washed look if you were diagnosing improper ring seating. A little more and you can see some shiny just melted aluminum poking up through the chewed up carbon. A little more than that and the piston starts melting around the edges. A little more than that and what often happens is bits of melted piston from the edge all around goes down and sticks the rings and that is when the smoke starts pouring out the exhaust! Look for all that going on within about a half inch of the outside diameter of the piston all the way around its circumference.
    #30
  11. Sniper X

    Sniper X De Oppresso Liber

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    I do too, and here's another weird thing, I get worse on premimum than on mid grade...I assume because I live at a high altitude. And i have heard at higher altitudes it is a waste to even buy permium gas.
    #31
  12. Rapid Dog

    Rapid Dog bikes, booze, broads...

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    PM'd ya supershaft....:deal
    #32
  13. Ron In Buffalo

    Ron In Buffalo Adventurer

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    I experience the same thing with fuel mileage you have w/ yours until I change the "needle jets" not the needles my fuel milege increase form the mid to high 30's to low 40's around town to mid to high 40's on the highway. Ron
    #33
  14. czycat

    czycat Adventurer

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    Nice conversation - is it dead now? Pretty new to the posting, but enjoy the reading. Any others have experience with putting in hotter cams? I'd love to get some more top end out of my gspd, but without replacing everything from carbs to exhaust. What's the word? Cams, 9.5:1 CR, simple head shave, or just carbs or exhaust? Still looking to keep up reliability for long distance rides in the future; just looking for a little more pull above 4000 rpms.

    SS if yer still out there, PM me - it would be great hear some more of your thoughts.
    #34
  15. Sniper X

    Sniper X De Oppresso Liber

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    bingo!
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  16. bereahorn

    bereahorn Long timer

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    :lurk
    #36
  17. KingsX

    KingsX Adventurer

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    I swapped out carb slide springs from a later model R100 series, they are wound coarser and keep the slide from
    coming up so fast....noticeable improvement for minimal bucks...I think 85 and up had the coarse springs.
    Also put a lower geared final in and I get 50mpg fully loaded if I keep it under 65, and replaced stock air filter with a Uni filter...pretty cheap way to get low and mid range response.


    Kings XXX
    #37
  18. DoktorT

    DoktorT BigBrowedNeandereer

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    I put the 3.2 in my 79 RS and just love it. Much better in low gears around town and can still do the ton all day long. Just much more usable for real use in all gears. With the 2.91, 5th gear is useless at less than 75mph or so. I did this so I could pull a trailer and it works super for that, but love it solo much better than the tall gears.

    As to fuel mileage, no change at all with the lower gears. The engine may be turning faster, but the better torque makes up for it. I get 48 to 49.5 mpg long range on the road typically at speed limit plus 5. That drops about 3 to 4 mpg when towing the Bushtec with some 300lbs gross load. I run it 300rpm higher than solo. The only time I got just over 50 is when I maintained 3rd anfd 4th gears at 50 to 65mph for a full tank or more. Less wind resistance at lower speeds is just lots more efficient.

    I had a new 76 R90/6/S years ago. Just right at 50 was typical. Recorded 53 once on a group ride all day in 2nd and 3rd on mountain twisties.

    Both machines are maintained stock and precisely tuned and balanced. The S fairing is worth a mile or two per gallon. The RS is better still. 45mpg rule of thumb is good for a bare 100/7.

    Like so many things Supershaft says, it's just his customers get poor efficientcy due to his by guess and by golly seat of the pants ideas. If he knew how to tune them properly, they would get the same results. Maybe as well that his clients tend to be heavy on the throttle in high gear. Cafe types trying to keep up with the riceburners. That would explain the 10mpg waste of fuel and danger to the public general and falling off the bike for a few weeks of physicians interests. How many times has he screwed the pooch? At least 5 times before this recent shunt. Are you going to take the advice of someone who thinks broked bones are required from time to time if you know how to ride or wrench Airheads?? I would want anyone who demonstrably cannot ride in a safe manner to keep his hands and tools off my Airhead, thank you. Stupid procedures yield stupid results.
    #38
  19. danedg

    danedg Horizontally Opposed

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    My 95 R100M has great response and torque thoughout the range with the 40mm Bings....lousy mileage!

    My bad...they are 32mm Bings!
    #39
  20. Plaka

    Plaka Brevis illi vita est

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    It's the smaller intake and exhaust giving you the torque. Try going one size smaller on the needle jets and get very accurate about tuning your idle settings and then watch your head temperatures. if they stay reasonable you should see an improvement in the mileage. But mileage drops off quickly over 65mph, and even more so on an open bike.

    IR thermometers are getting pretty cheap these days and $30 will get you a decent one. It won't have lenses that let you shoot a small spot from any distance but you can still get a reading on your heads from the saddle while riding. Look for a "hold" button as a nice feature.
    #40