Maximizing Fuel Fill

[Aluminum_Butt]

Over in the Hexhead wrenching area, there's a thread on drilling a hole in the filler neck of the gas tank to allow air to escape (burp the tank, as it were).

 

I've noticed when I fill the GT, that if I fill it all the way to the top of the filler neck, the level drops after a few seconds. I can usually repeat this process 3-4 times, and get another 1/3 gallon or so in. But I've never understood why this happens. Does it have to do with air? If so, where does it escape? Where does the gas go?

 

More generally, what techniques will maximize the fuel fill? The hexhead thread mentions "rocking" the bike to get more in. It seems obvious that you'd get more in on the center stand. Anything else?

[Bruce C]

I believe that if you work at getting every last drop of gas in the tank you will contaminate the charcoal cannister with raw gas, doing it no good at all. Better to fill it to the restrictor ring once and leave it at that.

Bruce C

[ELP_JC]

Once you're right at the filler neck, I sincerely doubt you can put 1/3 of a gallon on the RS/GT. Besides the canister (which I don't have), you definitely need some room for expansion, so I'd leave it well alone.

[rdfrantz]

A couple of extra points, Bob.

 

The business about contaminating the charcoal canister, the Evaporative Emission Control Device, is that it is designed principally to handle vapors, but will also handle small amounts of liquid gasoline. Some particular amount of liquid gasoline will overwhelm it, and some amount will create a "slurry" of charcoal in gasoline. It is possible for this slurry to be ingested into the fuel delivery system with consequences that not only may prove very expensive, but very dangerous should the engine cease operating at at critical time.

 

A second point is that incurring the liability above is wholly unnecessary. In daylight, despite four years of queries, no one has yet reported a "straight path" road distance between gas stations in the US of greater than about 150 miles. Crossing central Nevada between California and Utah, at night, is the only route I'm aware of that definitely challenges the 150 mile limitation.

 

Riding at Torrey, at extremely elevated speeds, we've found that all our K12RS bikes can cover the 154 miles from Hanksville, around the mountain South of Lake Powel, recrossing the lake to Ticaboo without even illuminating the low fuel warning light. That's a severe test of fuel consumption, but perhaps not the most severe possible. Very intense throttle application in low gears across very tight mountain roads, as in more eastern Arizona, would have a more negative affect than the high speeds in the more upper gears we use on that Torrey route.

 

My overall assessment is that when I ride my K12RS out there in even the most desolate parts the real world, rather than the "The World of Suppositional Worry", my gas tank serves me just fine when I stop for gas when it's available, rather than Press On Regardless.

 

Best wishes.

[Aluminum_Butt]

Thanks to all who replied. Clearly, I've been trying to do the wrong thing. I didn't HAVE to squeeze an extra 10 miles a tank out, but I just couldn't help myself when with my RT-riding friends who can pull 200+ out of a tank. I'll stop at the filler neck the first time from now on.

[ShovelStrokeEd]

Good thing you don't hang out with anybody with a GS Adventure.

 

I try to get a consistant fill which, I find, is someplace above that first cutoff. Actually that few extra seconds of bumping in the last little bit can make a difference in miles per tank which, if you cover many miles/day can make a little difference in your ultimate average speed or time to destination.

 

When covering maximum mile days my poor S is limited by its pitiful tank capacity. This causes me to do odd type ride plans based on tank capacity to maximize fuel utilization/miles covered. 4 tanks=700 miles=a good day's ride. I'm still working on the regression analysis for optimum speed. 85 mph GPS cruise means critcal gas need at 160 miles whereas 75 mph GPS cruise takes that out to 175 miles or so. Goal is to maximize miles covered in a reasonable time. Now that I look at it, it doesn't really matter until the milage difference becomes a divisor for a tank of gas which, in this case is 10 tanks or further than I want to ride in a day. According to my GPS, the difference in running hard with the extra ticket risk is 6 mph on the overall average speed. That means, in a 10 hour day, I'll get 4 miles further down the road running 85 than I will running 75. My speed average, with fuel stops, goes down to around 62 at 75 from the 66 at 85. OK, that means no more speeding. Average speed is determined more by # of fuel stops than by running speed. My GS should have showed me that as I could get a running average speed of over 70 really easily with that bike. Ditto my LT. Next bike is gonna wind up with a bigger tank, for sure.

[Caseyd]

So how many gallons are you putting in when you fill up? I agree with Ed, the speed at which I cruise or rate at which I accelerate controlls the range, but I always try to get gas 40 miles after the light comes on, which is very low on the fuel gage, but even when I incorrectly fill the tank the VERY top I only get 4.3 gallons. The manual says it has 5.5 - what gives?

[Aluminum_Butt]

Wow...only 4.3 after 40 miles with the light on? I can usually put 4.5 in *as soon as* the light comes on. 40 miles after the light I'd be on fumes.

 

Is there a calibration that can be done on the tank sensor?

[Aluminum_Butt]

OK, that means no more speeding.

Yeah, right.

 

Otherwise, excellent analysis as usual, Ed. I hadn't thought about it in those terms.

[CA1200]

It sure would be great if BMW would take a hint from others and put a larger tank on the K. Just think of a 6 gal tank. It is not the milage I complain about. It is the many stops to the pump because of the 4+ tank.

 

I can remember having to stop up to 4 or five times a day. Not fully because of being out of gas. But being low and not knowing where the next station is....it was a trip around the coast and such in CA. Got up and traveled til tired or dark.

[Knappy]

I agree with you. Also asking if there is a calibration that can be done? Mine on the last trip still showed 1/4 tank when the light come on. Now I question should I believe the gage or the light?

[ShovelStrokeEd]

Neither, believe your trip odometer. 2 full tanks and you will have calibrated it close enough for it to be more reliable than either. Take into account that a day of agressive twisty bashing or sweeper madness might increase fuel consumption and then find the envelope. You know tank capacity. Assume say 40 mpg and 4.7 gallons total capacity. That should give 188 miles dry to dry. Now you don't want to run that far, but 160 is certainly reasonable, except maybe in the desert. Where is the problem?

[Aluminum_Butt]

I agree with you that the trip OD is a great guide, but his 03 KGT should hold 5.5 gallons, I think.

 

When my light comes on, I can usually put about 4.5 gallons in - which implies a gallon reserve as BMW advertises. Light usually comes on between 160 and 170 miles. I've always assumed I'd be dry at 200 - 210.

[ShovelStrokeEd]

Assuming can be bad for you. Stick a plastic, one gallon gas can onto the back of the bike and go riding. Take it out till it sputters or, do as I do and just keep pushing till you eventually run out. AAA will bring me gas.

 

So far the two best I have gotten on the S are 188 miles, it took 4.7 gallons, which is the full capacity of the tank with nary a sputter and 192 miles which took 4.6 gallons to full. I don't trust the warning light at all as it can vary from 135 to 155 miles and I still can run to 170 to 180 miles without running out. A lot has to do with the density of the gas you put in. The stuff laced with ethanol will bring the warning light a good deal sooner. I pretty much gas up every time at the 160 mile mark, only pushing further if no gas opportunity presents itself. So far, I've only gone to a dead engine once and I that happened on an off ramp in Oklahoma and I was able to blow the stop sign and coast up to a pump.

[ELP_JC]

The official figure is 5.4 gallons for both the RS and GT; it was revised down from 5.5 in the sales brochure in 2003 (yes, my manual still says 5.5). In addition, not all fuel is usable, so never count on the full capacity. This is especially true on bikes with fuel pump inside the tank (like ours), which is cooled by the fuel.

I try to never run it below 1/4; I usually get over 150 miles at that point, plus I'm ready for a break anyway. Good day.

[swmckinley]

After purchasing my 04 KGT I ran out of gas on the third tank. This happened because the low fuel light was malfunctioning and not coming on, A trip to the dealer fixed this problem, however I noted that on that tank I ran out @ 195 miles with mixed use city/highway and was only able to put 5.2 gallons in the tank on the re-fill, which leads me to believe that there is a small percentage of resident unusable gas.

[cranezilla]

Coldfoot, AK to Deadhorse, AK 250+ miles no gas station, gravel road, overfilling the tank still won't help you.

Carry extra an gas can or install as aux tank, then you don't have to worry about getting the last drop into your tank.

Why do so many people worry about getting the last drop possible into thier tanks that they drill extra holes in the bike for the sake of 2 cc's of fuel, kind of paranoid don't you think.

If you need more fuel get a 20 gallon fuel cell from Summit racing and insatall it instead of a passenger seat, after all hauling apassenger around just cuts the MPG.

[3rdbike]

Read with interest your post about range versus speed on your 'S'. Sometimes when Angela and I go for a ride, I'll take my 'S'. She has a Suzuki 650 Savage. We've established 60-65mph as a cruising speed on New Mexico blue hiways. At this speed, I'm in 4th or 5th, running on just a 'whiff' of throttle. I've seen 60mpg from the 'S', riding like this. At the other end of the spectrum, I've seen 50mpg, running at a steady 5k rpm/90 mph.

[ShovelStrokeEd]

I hardly ever see that good. I got 180 or so miles on a tank back a couple of weeks ago when travelling from Albuquerque to Tucson via 180. Of course, I made the run from the intersection of I-40 and I-25 to Socorro in about 45 minutes, which might have hurt my milage a bit.