78 R100RS Mileage

[airraceaddict]

So, I had been noticing a slow decrease in the mileage on my bike over the last couple of years. I talked to Fred at Big Twin in Boise and also noted that it seemed to be running rich enough to be able to smell it after warm up. No other indications were to be had. Fred's a freakin genius. He said "oh, that sounds like a new needle and needle jet are needed." So, after I got home, I ordered the parts. For around 35 or 40 dollars, I think. Anyways, I "threw" the new parts in, tweaked the carb settings per Snowbum's instructions, went for a 250 ride and BAM! Just like that, went from 38-39 to 53.4 mpg! Checked the plugs to make sure it wasn't running too lean. No problem. Perfect. So, chances are, (and I did see something on another thread about gas smell at speed), there are others out there who could make this same repair and achieve pretty good results. Especially if, (and I have never messed with anything except the floats in 100k) you have high miles and never changed these. Fred was kind of surprised that I got that much of a result, "boy, you are back to factory spec!" but he also said it wasn't uncommon to get another 12 average. I went 250 miles exactly before I switched to reserve which is about the distance I was used to. So there you go. A happy experience at little cost and a BIG difference in fuel savings. Just make sure you get the same jets called out for per the numbers on the jets you remove or factory spec if someone changed them for some reason, (stamped on the side) and that you put the needle at the right setting. Cheers, and hope you get the same result I did, (a fairly drastic increase in mileage on a high mileage bike).

 

[20774]

ARA -

Yes, needles do wear...I would think they wear more than the jet. Also, it's possible that your floats are getting heavier and not floating as much, thus creating a more rich situation.

But still, that's great. Make one change...see the results.!!

 

[r100rt_mark]

ARA ÔÇô The routes I ride and my style of riding must be very different from yours. Both my 93 R100R and my 94 R100RT are relative low mileage bikes in excellent health, and I keep a careful of my bikesÔÇÖ fuel consumption. With either bike, my typical around Atlanta commuting blast gives me 35mpg on 87 octane with 10% ethanol. I see 42mpg on longer routes at gentler paces. The biggest difference in economy and ride quality I see happen when the carbs are lose sync. Easy to get back 2 or 3 mpg and relative smoothness with a quick balance.

 

[airraceaddict]

ARA ÔÇô The routes I ride and my style of riding must be very different from yours. Both my 93 R100R and my 94 R100RT are relative low mileage bikes in excellent health, and I keep a careful of my bikesÔÇÖ fuel consumption. With either bike, my typical around Atlanta commuting blast gives me 35mpg on 87 octane with 10% ethanol. I see 42mpg on longer routes at gentler paces. The biggest difference in economy and ride quality I see happen when the carbs are lose sync. Easy to get back 2 or 3 mpg and relative smoothness with a quick balance.

That makes me somewhat curious Mark. I run 91-92 octane alcohol free when it's available. I know this is a little off line, but when I use the same fuel in my Mazda B4000, (94), my mileage is better and a no pinging with 90-92 WITH alcohol. Pings like crazy with 87 and alcohol. The 78 was designed with higher octane and lead content with no alcohol. It would really be interesting to see what your bike would do in my neck of the woods. I know the blends are definitely different but I am also at 2200' ASL. I don't know. 42mpg isn't unreasonable but 35 sure seems high. On teh other hand, it's a hell of a lot better than 20-25 in a car.

 

[doktortim]

Expect to see visible wear of the needles and needle jets around 30k miles. They do wear out together. Hold the jet up to a light and you can see just how round or not it remains.

Keep the MPG's up. Replace the needles and needle jets at a regular long interval determined by inspection for wear. That emulsifier stack holding the needle jet in there needs to be kept clean anyway. Just a moment more and the needle jet can be checked.

 

[r100rt_mark]

That makes me somewhat curious Mark. I run 91-92 octane alcohol free when it's available. I know this is a little off line, but when I use the same fuel in my Mazda B4000, (94), my mileage is better and a no pinging with 90-92 WITH alcohol. Pings like crazy with 87 and alcohol. The 78 was designed with higher octane and lead content with no alcohol. It would really be interesting to see what your bike would do in my neck of the woods. I know the blends are definitely different but I am also at 2200' ASL. I don't know. 42mpg isn't unreasonable but 35 sure seems high. On teh other hand, it's a hell of a lot better than 20-25 in a car.

Have to get well outside the metro area here to get non-alcohol fuel, but I get a very definite improvement in mpg when the bikes sip the real thing. Probably 10% better, but I normally only get to check mpg on one tank full at a time, which does not get much opportunity to smooth out measurement variables. The real hit on mpg is my commute ÔÇô 15 miles one way, 1st 25% suburban surface streets, then a 70 to 80 mph Interstate blast (to keep up with traffic and out of trouble ÔÇô and this is a 55 mph posted highway), with the last 25% back on surface streets. 35mpg week in, week out (my 2005 Acura RSX averages 25 mpg on the same duty cycle). Head for the north Georgia mountains on a longer trip and 40 mpg is normal, more if less heavy-handed or lightly loaded.

 

[m_stock10506]

Already mentioned, Floats - especially with E10 gas these days. Also, when did you last replace the crossover fuel line that runs thru the air chamber? That fuel line will deteriorate and release gas fumes. When I started trying to fill up with non-alchohol gas - even alternate fill ups - my mileage improved by 2 to 4 mpg.

 

[airraceaddict]

Already mentioned, Floats - especially with E10 gas these days. Also, when did you last replace the crossover fuel line that runs thru the air chamber? That fuel line will deteriorate and release gas fumes. When I started trying to fill up with non-alchohol gas - even alternate fill ups - my mileage improved by 2 to 4 mpg.

Actually, I replaced the fuel lines when I went through the bike winter 09-10. Ordered it from Bing. Clear green tubing. They didn't stock the braided cloth covered tubing at the time. Guess they must have got an earful from BMW afficianados to source it again.......... As far as the floats, they are good to go. I replaced them a few years ago and didn't need any adjustment this time around. Float levels were still spot on. And no leaking, Thanks for mentioning that though. As Tim mentioned, at the top of the venturi, where the atomizer and needle jet meet it, the area surrounding the body where the venturi screws in at the top of the threads had what appeared to be remnants of a chewed up oring. (The oring on the venturi was totally intact). On the right side only. I'm thinking that was degraded rubber from the original tubing. It may have been partially responsible but pretty sure the jet and needle were "the cure."

 

[Polarbear]

Good post

I'm still learning. My R100/7, Ive owned since new and I don't remember the mpg's back then, but! Rode it yesterday 2UP for 500 miles through the Sierra Mountains, got 43mpg. I don't think I'v e ever changed my needles in 380000m! I WILL look see at them, because of this thead, good tip. Randy