Fuel Mileage...

[wmax351]

My bike's fuel mileage is sucking. 34mpg on a trip tonight. Pretty much all freeway cruising (45 miles or so at 65-75 mph), with a couple miles some slower town cruising. What gives?

I had checked all the sensors over winter break. All the values were good.

Valve clearances were checked 7k ago, and corrected to spec: Intake on the tight side, exhaust on the loose side.

No vacuum leaks that I can tell. I will double check, but all the rubber is good. This includes the PCR tube.

Spark plugs are pretty fresh, and fuel injectors are only 5000 miles old.

I need to do a compression test. A year ago, I checked it a while after having sea-foamed one of the cylinders (I stopped, bc I was having trouble starting due to bad starter brushes.). 155, 185, 195, front to rear, with the front cylinder having been sea-foamed, iirc. I have since sea-foamed all of them,  but haven't gotten around to checking compression. The mileage has deteriorated more recently, from low 40's to mid 30's now.

The question is, what could be doing this? Is my engine just wearing out? It only has 93k on it so far.

If that is the case, is it possible to tear the engine out from the front, rather than the rear? Seems like it would be an easier approach, since everything rear of the bellhousing is perfect.

[Scott_]

Well, as far as the mileage goes the more I get above 55-60 the less I get for mpg. I can loose as much as 10mpg with the higher speeds and, of course, other external factors as wind, hills, how loaded, etc......
Is it possible that it was just a fuel specific issue with this trip? ie bad gas. What octane fuel are you using.

As far as motor replacement, no you can't "take it out" from the front. Everything bolts "from the rear"

You could have developed a vac leak, it's easily checked for.
Spark plug wire come loose? Leaking spark from age? how old are they.

[wmax351]

Well, as far as the mileage goes the more I get above 55-60 the less I get for mpg. I can loose as much as 10mpg with the higher speeds and, of course, other external factors as wind, hills, how loaded, etc......
Is it possible that it was just a fuel specific issue with this trip? ie bad gas. What octane fuel are you using.

As far as motor replacement, no you can't "take it out" from the front. Everything bolts "from the rear"

You could have developed a vac leak, it's easily checked for.
Spark plug wire come loose? Leaking spark from age? how old are they.

Spark plug wires are in tight. They may be a bit old, but I haven't seen any arcing.

I need to check the vac leak again, as well as the compression/leakdown.

The fuel mileage has been relatively constant. Lower if I am loaded more, or having more fun (IE: fast acceleration on twisty roads).

Running 89 octane. No problems with it.

[mystic red]

+1 on the spark plug wires. Check the plugs also, fresh or not.
In the last year I've had bad plug wire on the K11, bad plug wire on my Buick and a bad plug on my wife's Honda. :loco:
It'll kill your mileage plus it's easy to do. Wires don't need to be arcing to be bad or it might be a short arc that's hard to see.

[wmax351]

+1 on the spark plug wires. Check the plugs also, fresh or not.
In the last year I've had bad plug wire on the K11, bad plug wire on my Buick and a bad plug on my wife's Honda. :loco:
It'll kill your mileage plus it's easy to do. Wires don't need to be arcing to be bad or it might be a short arc that's hard to see.

Good to know. I'll see if I can get some of those if the compression checks out.

[Chaos]

My mileage had dropped into the mid 30's from the mid 40s,  180k and never touched the injectors.  My K&N air filter was pretty plugged up (I sorta forgot about it for the last decade) and I ran a bottle of Techron through 2 tanks.  Mileage came back up, not sure which fix did it. 

[wmax351]

Looks like its burned a good ammount of oil too... from mid-upper window to the bottom, in <1k miles.

[Scott_]

About the plug wires, if memory serves me correct on the K75's you can't test them with a regular ohm meter as they have an arc gap in the cap that is different than the wires we have on the 1100's.

Someone correct me here if I'm wrong.

[wmax351]

About the plug wires, if memory serves me correct on the K75's you can't test them with a regular ohm meter as they have an arc gap in the cap that is different than the wires we have on the 1100's.

Someone correct me here if I'm wrong.

that is correct. the k75 has spark gap. the 100 and 1100 have resistor caps. aftermarket wires have reistor caps as well. i may make my own. will end up costing ~20 bucks for the set.

[wmax351]

I pulled the plugs. All are oil and carbon fouled, and the pistons are coated with lots of carbon.

I couldn't do the compression test, because the freebie rental from Kragen didn't fit the 12 mm plug. Will figure that out later.

[Scott_]

I couldn't do the compression test,.........didn't fit the 12 mm plug.

I had the same issue a couple of years ago, my current gauge at the time didn't fit either. My neighbor(Mac tools man) happened to have one of the "original" compression testers with the rubber plug on the end that you just have to hold against the hole.

I have since purchased a tester with the 12mm adapter. It wasn't that expensive if I recall.

[wmax351]

I couldn't do the compression test,.........didn't fit the 12 mm plug.

I had the same issue a couple of years ago, my current gauge at the time didn't fit either. My neighbor(Mac tools man) happened to have one of the "original" compression testers with the rubber plug on the end that you just have to hold against the hole.

I have since purchased a tester with the 12mm adapter. It wasn't that expensive if I recall.

I have one at my Folks house, but its 25 miles each way. I may go to harbor freight, and buy a cheap one.

+1 on the rubber ones. Much easier, IMO. Although you need a third hand to run the starter.

I'm thinking of just picking up an engine and transmission for 250 dollars from a guy in the bay area. http://sfbay.craigslist.org/sfc/mcy/2959078880.html


Or 400, (i'll offer 300) for this:

http://sfbay.craigslist.org/pen/mcy/2971270596.html

[Duc750]

Park it on the side stand much ?

I know we all know about the side stand issue but it seems really bad on some bikes - my k100 from years ago had no great issues but If I take the 1100 into work I often have to park it on the side stand due to the ground where I park - If I do that it costs me 200 ml in oil straight away - Ok no biggie but....... If I do it for 5 days on the bounce I see my mileage drop from 45 (proper) mpg down into the high 30's until; I clean the plugs (which by now are covered in shite !

Its a bizare state of affairs but I never use oil otherwise - the oil consumption was driving me nuts until I isolated it back to purely parking on the sidestand. I've used nearly 8 litres since the last service (including the last service) (now on 5K) but I'm happy I know the cause of both my poor gas mileage and my poor oil consumption !

[conybeare]

I have a similar issue, and I believe it's just from worn rings. My gas mileage is terrible in the city (34-38 mpg) but perfectly normal on highway trips (around 50 mpg). Well, it on highway trips it starts low, but gets progressively better over the course of a few tanks. The plugs do have a bit of oil fouling, so I figured that riding high revs (5k plus) for a tank or two was just cleaning the plugs. That obviously doesn't solve the oil-burning problem, but topping off here and there seems like a better option for me than a rebuild or replace, at least right now...

Have you noticed better mileage on the highway? I mean, more so than you would expect from the normal difference in mpg between city and hwy?

[frankenduck]

Dan:  Try a can of that Restore stuff.  It's not a "rebuild in a can" but it does work at improving compression.

[wmax351]

Timing seems to have done the trick. 41 mpg from Mill Valley to Sacramento to Berkeley. 95% of the miles were done at <65, 90% at ~80. This is with a windshield, on a naked bike, with high bars, too.

Will check the plugs later. It doesn't seem to have burned much oil, if any. I refilled to the top line for easy measurement.

[orforester]

Put in right at 300 miles today, temps in 70 to 80.  Up over Willamette pass and in traffic in Eugene, stopping alot for construction, purred along at speed limit or a little above. Got closer to 50 MPG.  Like 51 on one tank, 130 miles.  Last year it was 40 to 42.  Maybe it likes warmer temps, unlike me!

[frankenduck]

FYI: Engines generally perform better with cooler intake air. (I forget the exact reason - maybe because its denser?)

[conybeare]

Dan:  Try a can of that Restore stuff.  It's not a "rebuild in a can" but it does work at improving compression.

You don't think this has any unwanted side effects or potential for damage?

[frankenduck]

Dan:  Try a can of that Restore stuff.  It's not a "rebuild in a can" but it does work at improving compression.

You don't think this has any unwanted side effects or potential for damage?

Nope.

[Scott_]

I think that's the same stuff Shog's used on the "shop whore" to bring it back from poor performance and weak compression.

[Duc750]

FYI: Engines generally perform better with cooler intake air. (I forget the exact reason - maybe because its denser?)

Thats the one - hence why Ram Air kits are out front on the bike - AT hi speeds you get a bigger charge of air but at all speeds you get cooler denser air as its not tyring to suck it past a very hot engine/rad/exhaust.

Worth about 2 rwhp on my old tl1000 race bike on the dyno - It was the sort of modification I could handle playing with, without a full strip down !