a few more things that i'm coming up with now that i'm getting close to buying a bike.

how much does jetting + installing lunch box + installing aftermarket exhaust reduce the mileage? just wondering if i would want to buy a bike like that or not.

i forgot my other question i'll post it as a response in a bit

I don't know my jetted/jardine exhaust/lunch box gets 50 mpg consistently, plugs read great.  It's a 93.

good to know! thanks much.

to increase your mileage (when you find that 50-55 MPG is not enough ) you can install bigger front sprocket, 17 or 17 tooth.
You will not be able to accelerate that fast but your mileage will be better.

I do not think you should hesitate buying the bike that has been rejetted, lunchboxed and piped.
after all 50 MPG is still a great result compared to average car.

Quote from: kml.krk on June 22, 2009, 05:11:43 PM
to increase your mileage (when you find that 50-55 MPG is not enough ) you can install bigger front sprocket, 17 or 17 tooth.
You will not be able to accelerate that fast but your mileage will be better.

I do not think you should hesitate buying the bike that has been rejetted, lunchboxed and piped.
after all 50 MPG is still a great result compared to average car.

well, yes and no. motorcycles yield a really nice mpg (and FUNpg) if you only concern with moving one person.

if you look at the actual power vs weight moved, and the subsequent mpg, bikes really, really SUCK at mpg.

a 4 cylinder car (2400cc) moves almost 4,000 lbs, and gets 30-40 mpg, depending on the driver.

a 2 cylinder (500cc) bike moves less than 800 lbs including rider, and gets -only- 50 mpg. 1/4 the weight, and only 25% better gas milage.

neat stuff math (i usually get it wrong

Quote from: ohgood on June 22, 2009, 05:33:22 PM

Quote from: kml.krk on June 22, 2009, 05:11:43 PM
to increase your mileage (when you find that 50-55 MPG is not enough ) you can install bigger front sprocket, 17 or 17 tooth.
You will not be able to accelerate that fast but your mileage will be better.

I do not think you should hesitate buying the bike that has been rejetted, lunchboxed and piped.
after all 50 MPG is still a great result compared to average car.

well, yes and no. motorcycles yield a really nice mpg (and FUNpg) if you only concern with moving one person.

if you look at the actual power vs weight moved, and the subsequent mpg, bikes really, really SUCK at mpg.

a 4 cylinder car (2400cc) moves almost 4,000 lbs, and gets 30-40 mpg, depending on the driver.

a 2 cylinder (500cc) bike moves less than 800 lbs including rider, and gets -only- 50 mpg. 1/4 the weight, and only 25% better gas milage.

neat stuff math (i usually get it wrong

I'd still rather get ~60mpg on my bike by myself than drive around in my car and get like 25 mpg in my car by myself.

ok i remember my next question.

i've been messing around with engines in various cars for a pretty good while now, including some very extensive jobs on complicated cars. i never have though actually conducted any sort of engine "rebuild" at home. i'm wondering, likelyhood of needing it aside, if i get a high mileage bike, is there any kind of write up around for rebuilding this engine? everyone tells me it's just general knowledge so there are no write ups, but i just feel like i need a guide for the first time i get into the internals. btw, i also understand that once it's taken apart, i'll need to take it to a machinist to get it honed and all that. i'm just talking about disassemble/assembly.

well, yes and no. motorcycles yield a really nice mpg (and FUNpg) if you only concern with moving one person.

if you look at the actual power vs weight moved, and the subsequent mpg, bikes really, really SUCK at mpg.

a 4 cylinder car (2400cc) moves almost 4,000 lbs, and gets 30-40 mpg, depending on the driver.

a 2 cylinder (500cc) bike moves less than 800 lbs including rider, and gets -only- 50 mpg. 1/4 the weight, and only 25% better gas milage.

neat stuff math (i usually get it wrong

But how often do you really need to carry around 4000 lbs?  Most of the time the only real weight you are carrying around is the car itself.

yeah that's pretty weird about the fuel mileage. i can understand how smaller engines though could start to be less and less efficient.

anyway, does anyone have the down-low on rebuilding this engine at home? i'm not a machinist, but i'm fairly certain i could do the dis assembly/assembly

I agree with ohgood's point but not his figures.  4,000 lbs for a 4-banger cage?  More like 2,800 with driver, 2,900 with really fat driver.  And 400 lb. GS + 200 lb. me = 600 lbs, not 800, but his point is well taken.  For their size and mass, bikes suck gas.  This is mostly due to high power to weight ratio compared to cars.  I can only squeeze 39 mpg out of my stock XS 750 triple with its modest 64 HP.  What's up with that?  The GS is really a gas sipper as bikes go.

Anyway, my GS averages about 60 mpg since I bought it and it's stock other than V&H pipe and K&N drop-in filter with the restricting ring installed, and I have a 17-tooth front sprocket.  I bought the sprocket to improve highway performance, and boy, did it ever, but strangely, I didn't notice any change in mpg.  My Fuelly still says what it says, as you can see below.

that's interesting. has anyone tried driving the bike engine like a car engine, and not tacking more than 4k or so? maybe that would get some really good gas mileage.

anyway, what improvements did the 17 tooth make? just drop the rpms? that's cool but i definitely wouldn't care to do it if it didn't improve gas mileage.

Quote from: KasbeKZ on June 23, 2009, 08:03:12 PM
yeah that's pretty weird about the fuel mileage. i can understand how smaller engines though could start to be less and less efficient.

anyway, does anyone have the down-low on rebuilding this engine at home? i'm not a machinist, but i'm fairly certain i could do the dis assembly/assembly

Nothing weird about the fuel milage. Bikes have totally sucky aerodynamics, and relatively large engines for their size. Run anything 55MPH and the vast majority of fuel goes to overcoming air resistance. Faired bikes still suck rocks compared to cars.  IIRC there is or was an Indian (the country, not the brand) one-cylinder diesel bike that gets upwards of 100 MPG - and presumably has all the power of an old lame hamster running fitfully in a wheel.

As numerous full rebuilds documented here repeatedly demonstrate, a used engine generally costs less than a full rebuild. The Clymer, Haynes, or factory manuals will cover the process if you opt to go that route, but given the large number of bikes available with less than 25K miles and Jack's experience with getting 80-100K miles out of a GS engine, might not be much to worry about. Keep the exhaust valves on the loose side, keep oil in it, change the oil, and ride it.

haha i keep forgetting about service manuals. my last car was considered "too complicated" to have one so i've been putting all my questions on forums and such.

but thanks much for that response. that does put an end to my wonderment.

ok someone please give me their opinion on how risky it is to get a bike with 12k on it. i want to jump right onto it with very little maintenance and use it as my primary commuter for several years, so it will get between 5 & 10k each year. i'm trying to avoid really doing anything major to it. is there much risk as long as the compression is good and the oil pressure is good?

I would trust a 12,000 mile bike more if it was ridden regularly. Everybody just thinks less miles per year so maybe a 12,000 mile bike that is 20 years old is worse because seals could be brittle, carbs clogged and stuff. But a 12,000 mile bike only 2 years old everything will probably be fine. Just look for obvious stuff, damaged from falls, suspected of being repairs, ask if it's salvaged, oil leaks, smoke on startup. 12,000 is fine on a GS, some would consider it barely broken in. I'd probably get nothing from my bike even though I know it's reliable still at 32,000 miles. I just did an all out high speed run to Nevada to buy fireworks. Almost full throttle the whole way averaging an indicated 95-100 mph and it never missed a beat even with my bikes "advanced" age. Checked the oil after 650 miles of nonstop high speed running, not a drop consumed, and all this at 32,000 miles on the odometer. I'd say this engine is as durable as you can get.

thanks that's good to know. i'll def. be checking compression though before i buy one just to get an extra varification. it looks like it may be soon. i settled on a price with someone today and i hope he comes through

Oh yeah and as for riding like a car, I do it myself, short shifting and opening the throttle wide instead of revving at partial throttle. With my 18 tooth sprocket I average 70 mpg. I've seen as high as high as 85. This fireworks run was my new low previously it was 60 mpg or so. 51 mpg but that's with a headwind, uphill at full throttle most of the time running at 95-100 mph. So I think 51 being my rarest of rare occasions is pretty good.

18 teeth? isn't that 3 up? that sounds like a good goal for me to shoot for lol. that's exactly what i want. so where do you shift? 4k or so?

Quote from: KasbeKZ on June 27, 2009, 04:18:29 AM
18 teeth? isn't that 3 up? that sounds like a good goal for me to shoot for lol. that's exactly what i want. so where do you shift? 4k or so?

yeah, yeah, it is definitely 3 up... from 15T, but if you meant 3 up from stock then no, stock is 16T.
cheers

haha ok. 2 up.