> Yes, a #50 slow speed jet would waste fuel through the entire RPM range. Good catch there.

> Another place to look is the needle heights. Most carbs will allow you to see the needle clip, and thus the clip position. On the Bings the clip is concealed leading to 2 errors...

1. A very common mistake is to have the needles in different clip positions. You can most easily check for mis-matched clip positions by measuring the length of the exposed portion of the needle.

2. To check for correct clip slot, all you can do is remove and count while reinstalling.

 I have been away for awhile, but wanted to get back and re ignite this posting with where I am regarding my MPG issue.

 I have removed the carbs and purchased rebuild kits for them. I have the right hand carb apart and cleaned everything with Gum-out. It was a bit dirty, but didn't look as though it would cause the low MPG. However, things I have found along the way with the help of suggestions here is that the carb enricheners on mine are in fact marked L and R for each side. They are located correctly. Upon closer inspection I also found the idle jet on both my carbs is a #50, however on all the info I could find they are suppose to be #45. I am in the process of reassembly of the right carb and then I'll do the left. I also purchased new plugs. I will return back with an update when I get it all reassembled. Thanks for all the help.

If I were trying to tune/diagnose a “new to me” running airhead, I would, in this order;

1.  Set valve clearances.  
2.  Check compression.  
3.  Set ignition timing/confirm advance.  
4.  Tune and balance carbs. 

This is the right “pecking order” to tune the engine, and uncover issues. I have a feeling (at 30mpg) there may be carb/carb tuning issues, but you have to confirm 1, 2, and 3 before getting to 4. 

The compression check is something that you would only do with a “new to you” engine, to confirm it's condition. After that, a tune-up would be 1,3,4. (You might check the compression again in 10 years, or 20?)  That’s to say, you may be able to borrow a compression tester. Some might say this check is unnecessary, but, it would give me assurance that all is ok with the rings and cylinders, and the valves are sealing. 

Yes, great advice. Check to make sure that both enricheners are completely shutting off when the lever is in "off" position. It could be that one of your enricheners is not shutting off completely or that the disk is in backwards, or both. Both of these will lead to rich running.  My enrichener cables took a bit of fiddling to get both to shut completely off. The choke cables should be in solid wire to allow them to "push" the enrichener disks into the closed position. 

@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

Sure! It is #47 in the attached diagram. I may not be using the correct term but it is a hollow disk that is part of the enrichener (choke) circuit. I assume you have Bing CV carbs on your bike as well? You should be getting easily 200 miles from a tank of gas. I also have the 22 liter (5.8 US gal) tank and generally get about 200 miles before I hit reserve.

@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. 

  John Young

John -

The enricheners are disks that are mounted into the side of both carbs, under the square cover, on the engine-side. This this the device inside the carb that the "choke lever" rotates to add more fuel for starting. It is literally a round, flat disk about the size of a penny into which slots are cut to control fuel flow. 

There are 2 common issues with these disks...

• Because the carbs are mirror images and so very similar, the Left disk can be installed into the RH carb by mistake, and vise versa. And this leads to all sorts of issues. Some say that the disks are marked L and R for identification. 
• On both the earlier engine-mounted-lever and the handlebar-lever type, control cable adjustment is critical. The early engine-mounted style has to be adjusted to make the disk hit its stop at the same instant (or a fraction before) the enrichener control lever hit its stop. 

Check it !! Your mileage sounds awful.

 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

  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?