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MPG on an 1985 r80rt

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John Young
(@john-young)
Posts: 45
Trusted Member
Topic starter
 

 I'm in the process of learning my new to me 1985 r80rt. I wanted to get a approximate mpg. I used some Liqui-Moly shooter once the fuel tank was down to 2 gallons as instructed. I had to switch to reserve when my trip meter went to 130 miles. I guestemated I would get aprx. 35 MPG, however when my trip meter reached 155 miles I ran out of fuel. I had a mile walk to the nearest gas station. When I originally got gas I filled the tank to what I percieved as full. The tank capacity is around 5.5 gallons. my early calculation  is aprx. 30 MPG. If the is something anyone knows how to get the fuel tank full that would help get the tank full that would be great. I do not have a flap on my tank neck. MPG seems low on my bike, unless others think this is about right. I have seen estimates that vary widely: anywhere from 30 to 45 MPG. If anyone has a similar bike and can share their MPG estimates so I can get a better idea of what to expect it will be appreciated. Bike runs well, however have not touched the carbs yet.

 
Posted : 07/29/2021 11:00
Richard W
(@wobbly)
Posts: 2546
Member
 

I'm not really knowledgeable on the R80, but my '79 RT got 150+ miles out of a tank. I would have just turned ON the Reserve at 150 miles of mountain riding. The RT does have the lowest ratio final drive offered, but it's also a 1000cc engine. Running the full fairing probably helps too. 

Maybe an R80 owner can get you better numbers. 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 07/29/2021 15:27
John Young
(@john-young)
Posts: 45
Trusted Member
Topic starter
 

 Today rode the bike for about 25 miles. I varied the speed a lot and when coming to a stop and idling the rpms sat at around 2000 and after a few blips of the throttle it went down to around 1200. Read where the choke cables might be getting stuck. I have looked at the air filter and it looks very new. Not an airhead authority, but for what I can tell the bike seems to run great. The person I purchased the bike from said it had sat for a few years before he bought it and rebuilt the carburetors, put in a new timing chain and fresh battery. 

 My thought is to lubricate cable pulls. (Do cables themselves need lubrication?)

 Check the choke lever. It holds on the first stop but when I open it all the way it goes to full choke but does not hold there. I'm guessing it should hold at full stop so maybe the issue is right in this area.

 Eventually I will do a carb balance just to learn how it is done and maybe improve gas mileage. I have a Twin Max carburator balancing instrument and hopefully it will do the job. Have never used it so I look forward to learning how it works and use it on my bike. If anyone has used the Twin Max and has any suggestions please let me know.

 I hope others share the same enthusiasm I've had so far about learning BMW airhead technology and what makes the airhead simplicity so appealing. Or,.. maybe I just got in the game late!

  Thank you for being here and allowing me to be part of the community.

This post was modified 3 years ago by Richard W
 
Posted : 07/30/2021 15:11
David Elkow
(@4949)
Posts: 304
Reputable Member
 
Posted by: @john-young

when coming to a stop and idling the rpms sat at around 2000 and after a few blips of the throttle it went down to around 1200.

Are your valve clearances set properly?

 
Posted : 07/30/2021 18:55
Richard W
(@wobbly)
Posts: 2546
Member
 

Step-by-step notes on carb tuning...

  • At rest (throttle closed, choke OFF) you should have 1 to 2mm of free play in each of the outer cable sheaths. This allows the springs within the carb to close whatever they control. Without this "free play" the bike can't settle down to idle at 950 RPM. IOW, without free play the cables may hold your throttle(s) slightly open.
  • On the intake side of the carb, pointed at the floor, is a screw inside a well. That's the Idle Mixture adjustment. LIGHTLY run both those in until they touch, then back them each off by 1.5 turns.

?

  • Do this next part with the engine fully warmed... Along side the Mixture screw is a smaller protrusion. Remove the screw on the end. That is the vacuum port onto which you plug the rubber hoses from the TwinMax. 
  • Adjust in/out both the Idle Speed screws on the side (between the cab and engine) to achieve 950-1000 RPM AND at the same time have the TwinMax setting on Zero. That's perfectly balanced idle. 
  • Then, open the throttle throttle to about 1800 RPM. This time balance the TwinMax reading by changing the adjusters where the throttle cables attaches to the carb body. This balances the carbs at running speeds.
  • Unplug the hoses and BE SURE to re-install both screws that block the vacuum ports.
  • Check once more for outer cable free play.
  • You're done !

Hope this helps.

This post was modified 3 years ago by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 07/30/2021 18:58
Frank Jarrell
(@frankj)
Posts: 25
Eminent Member
 

I have a 86 R80 mono with a parabellum scout fairing. It should have the same rear end as yours (32/10). I have tracked my mileage on Fuelly.com the last 3 years or so. I am consistently getting 40ish MPG running on back roads at a brisk pace. I will have occasional tanks in the 45-50 range and occasional tanks in the 30-35 range. I fill the tank so that gas is just above the flapper valve in the fuel filler which gives me 150 to 200 miles to reserve. To get the tank full I put the tip of the nozzle so that it just holds open the flapper valve and the little sensor port is up in the filler neck. I try not to push the reserve past 30 miles.

 

A cause for the high idle is the ignition advance sticking. I would be sure the throttle and coke are closing completely first. You can push the levers down with your thumb to see if the are sticking. I keep my idle set around 1200 anyway to keep the oil flow up.

 
Posted : 08/06/2021 08:49
Richard W
(@wobbly)
Posts: 2546
Member
 
Posted by: @john-young

My thought is to lubricate cable pulls. (Do cables themselves need lubrication?)

There was a discussion about this maybe 2 years ago. I think the general consensus was that official BMW cables do not need lubrication. And it was left at that. (However, please note that ALL bets are off if you are not using official BMW cables.)

Having lubricated cables for many decades, that was a bit of info that stuck in my throat... I found it very hard to swallow. So I would tell you 2 things...

  1. IF you suspect that things are hanging up in the throttle system, then lubrication can certainly be tried. BUT, certain liquids that are sold as "motorcycle cable lube" will not play nicely with the PTFE inner cable lining. If you want to try cable lube, then restrict your choices to common ATF. I'm using common Dextron without any ill effects.
  2. Whether you lube the cable or not, you still need to remove the cable-end "barrel" from the lever and fill that void with water-proof grease, then reinsert the barrel. AND, you'll need to oil the handlebar lever pivot bolt. I find that common motorcycle chain lube does a great job of this. It penetrates in as a thin liquid, then thickens in place to stay in place. 

 

However, the most common issues with incorrect idle are the Auto Advance Unit sticking, and lack of free-play in the outer cable sheath (as previously explained).

Hope this helps. 

This post was modified 3 years ago 2 times by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 08/06/2021 17:00
John Young
(@john-young)
Posts: 45
Trusted Member
Topic starter
 

Thanks to all who have responded. Since my last post I have taken apart the cable connections at the throttle and cleaned out all the old grease and replaced it with Maxim waterproof grease. I think somebody once put a little lithium grease in as there was a dab of white grease on top of what looked like the original grease from the factory. Cleaned the part that holds both throttle cables along with the grip with the teeth that engages that piece. May have put too much grease in there but doesn't seem to effect the throttle response. I lubed both the right and left pivot pins.

 Today I tackled the carburetor balancing (thanks Richard) and set the idle to about 1100 rpms. May be too low but the bike seems to idle well although the Gen red light does come on once warm and idling.

 I had to engage my reserve tank today at 140 miles. But this was just after adjusting my carbs. The idle has now consistently gone back to 1100 rpms. When I filled up it took 5 gallons and there was 150 miles on my trip meter. I put ethanol free gas in this time and will see if that effects anything. Bike seems to run fine on the ethanol free gas. 

 
Posted : 08/10/2021 13:41
Richard W
(@wobbly)
Posts: 2546
Member
 

Another satisfied customer !  ? 

You're on your way now. 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 08/10/2021 14:12
John Young reacted
John Young
(@john-young)
Posts: 45
Trusted Member
Topic starter
 

 I have ridden my bike about 100 miles since filling the tank with non ethanol fuel. Previously I ran out of fuel and the reserve emptied.  About 40 miles before running out I put a fuel system cleaning liquid acquired from EME in the tank.

 So with all that being said, the last time I filled the tank with the ethanol free fuel the bike seems to run real well. I have adjusted the carbs during this time so there are different factors that might have contributed to it's perceived smoother running.

  So I am going to continue the ethanol free fuel and see if my mpg changes or not.

  If someone has other thoughts regarding fuel type I'd like to hear them. The good quality unleaded fuel I've been using is Mobil with detergent additives. They also carry the ethanol free gas I am using presently. 

 
Posted : 08/21/2021 15:46
Richard W
(@wobbly)
Posts: 2546
Member
 

Several things...

@ If you have not removed the front engine cover and inspected your ignition system, this is a good time. 1980 R80 originally shows points ignition and that will require mechanical and electrical maintenance. (Disconnect the battery Negative first.) Remove the cover, replace the points, condenser AND auto advance springs.

@ You must disassemble the auto advance unit and apply a dab of grease to the pivot points and where the ignition cam pivots internally on its post. Then some grease on the ignition cam itself. Set the points gap.

@ Then re-set the ignition timing using a ignition strobe lamp and the high-speed timing mark on the flywheel. (You may want to get a good look at the mark and possibly paint it yellow before you begin.) This is done at high RPM so that you are timing the engine at Full Advance. When watching for the mark in the timing window, as you slowly increase the engine to 4000 RPM, the mark should come up to the window pointer, but not go further even as the RPM is increased.

People don't realize how much engine smoothness that correct engine timing adds. I had a bike that had awful vibration in certain RPM ranges. I was about ready to sell it. I was just fed up with it. Then I re-set the timing and it became a whole different bike. A real joy to ride. 

@ When you change your timing, you might want to throw the TwinMax back on there for a quick re-check. Remember: 1) the correct idle speed is between 950 and 1000 RPM, and 2) you must have 1-2mm of slack in clutch and throttle cables.

 

I'm not opposed to non-ethanol fuels. If you can find "High Test" ethanol-free, I think it's generally a good thing. What I don't know is do they have the same levels of cleaners that the "High Test" ethanol fuels do. It certainly wouldn't hurt to add a tablespoon of your own cleaners... like Techron or StarTron.

Hope this helps.

We'd certainly like to hear more of your adventures and reports.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 08/22/2021 05:19
David Elkow
(@4949)
Posts: 304
Reputable Member
 

You are probably way ahead of me on this, but I don’t see it mentioned, so I’m gonna repeat myself: Be sure the valve clearances are set.  Having proper (sufficient, certainly) valve clearance is an essential basic requirement for these (solid lifter) engines.

 

 
Posted : 08/22/2021 10:20
Tobin Peever
(@tpeever)
Posts: 40
Eminent Member
 
Posted by: @john-young

 I'm in the process of learning my new to me 1985 r80rt. I wanted to get a approximate mpg. I used some Liqui-Moly shooter once the fuel tank was down to 2 gallons as instructed. I had to switch to reserve when my trip meter went to 130 miles. I guestemated I would get aprx. 35 MPG, however when my trip meter reached 155 miles I ran out of fuel. I had a mile walk to the nearest gas station. When I originally got gas I filled the tank to what I percieved as full. The tank capacity is around 5.5 gallons. my early calculation  is aprx. 30 MPG. If the is something anyone knows how to get the fuel tank full that would help get the tank full that would be great. I do not have a flap on my tank neck. MPG seems low on my bike, unless others think this is about right. I have seen estimates that vary widely: anywhere from 30 to 45 MPG. If anyone has a similar bike and can share their MPG estimates so I can get a better idea of what to expect it will be appreciated. Bike runs well, however have not touched the carbs yet.

No direct experience but it seems like you should get way more than 30 mpg from an R80. Unless you are driving around like a madman! I typically get 40-45 mpg (US gallon) on my R75/6. I actually think that is fairly dismal for a bike of this displacement since my '74 850 Norton Commando gets over 50. Mileage was worse when I first got the R75/6 (maybe 35 mpg) and I found out that a previous owner had installed the fuel enrichener disk the wrong way around. So that is something that might be worth checking. How do your plugs look? Rich? Needle position?

This post was modified 3 years ago by Tobin Peever
 
Posted : 08/25/2021 18:37
John Young
(@john-young)
Posts: 45
Trusted Member
Topic starter
 

@tpeever  Can you share with me the location of the fuel enricher disk? Bike seems to run very well, but my gas mileage has not improved. I just turned the reserve on both carbs while running with aprx 125 miles on the trip meter. That is with ethanol free gas. Probably the least amount of miles before turning on the reserve. I'll check the plugs again tomorrow and see how they look. Bike starts right up and idles smoothly.  I'm not bogging the bike and keep the rpms around3500 to 5000. Thanks in advance and for replying.

  John Young

 
Posted : 08/25/2021 21:00
John Young
(@john-young)
Posts: 45
Trusted Member
Topic starter
 

@4949 Hey David,

 Sorry for the late response. I'm checking the valves this coming weekend. I hope this could be the issue as I just turned on the reserve today with aprx. 125 miles on the trip meter. That is probably the lowest mileage yet. I used ethanol free this last fillup and not sure if there is any issues with it, however the bike runs great. Starts right up and idles around 1250 rpms. I don't bog the engine nor over rev it continuously. I'll post what I find when I do the valve check and adjustment. I see a lot of posts claiming pretty high mpg but it seems the average sits around 40 mpg. So far my average estimated mpg is about 30-32 mpg. It has the 5.8 gallon tank and after turning on the reserve I usually put in about 5-5.25 gallons. Thanks,  John Young

 
Posted : 08/25/2021 21:12
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