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Old 11-30-2010, 10:59 AM   #31
Sniper X
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Joined: Jul 2006
Location: Central New Mexico, 7420ft above sea level
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Quote:
Originally Posted by Airhead Wrangler
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.
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.
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Old 12-01-2010, 08:35 AM   #32
Rapid Dog
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Question pleaseadvise

PM'd ya supershaft....
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Old 12-01-2010, 09:57 AM   #33
Ron In Buffalo
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Quote:
Originally Posted by caponerd View Post
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.
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
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Old 11-09-2011, 01:50 PM   #34
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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.
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Old 11-09-2011, 02:36 PM   #35
Sniper X
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Quote:
Originally Posted by east high View Post
mikuni conversion?
bingo!
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Old 11-09-2011, 08:40 PM   #36
bereahorn
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Old 11-09-2011, 08:51 PM   #37
KingsX
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more low and midrange response

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.


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Old 11-10-2011, 05:37 AM   #38
DoktorT
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Quote:
Originally Posted by bmwrench View Post
You might also consider a shorter rear drive ratio. The stock R100RT ratio is 2.91:1. A 3.20 will really make it scoot. This is probably the biggest bang for the buck.
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.

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Old 11-10-2011, 09:15 PM   #39
danedg
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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!

danedg screwed with this post 11-11-2011 at 07:18 PM
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Old 11-11-2011, 09:23 PM   #40
Plaka
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Quote:
Originally Posted by danedg View Post

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

My bad...they are 32mm Bings!
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.
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Old 11-16-2011, 09:13 AM   #41
danedg
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But mileage drops off quickly over 65mph, and even more so on an open bike.




I'm having a real problem with keeping it under 65....
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