What might cause a 10 mpg drop in my fuel mileage

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burkbuilds
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What might cause a 10 mpg drop in my fuel mileage

Postby burkbuilds » Mon Feb 14, 2011 12:24 am

I've put over 30,000 miles on my 500 since I bought it in May of 09, and it has been a very trouble free bike for me. I changed my gears out to 17/40 not long after I purchased the bike and I've been getting 58-60 mpg consistently since then up until about a month ago. My mileage dropped off to about 55 mpg and now I'm down to 50 mpg. I thought it might just need to have the valves adjusted, so I did that today and got them all set to mid values (several were on the tight side of the spec and one was loose) and although I felt like the bike had a little more pep than it has had lately, I just drove down to Atlanta and checked my mileage when I got here and I'm dead on 50 mpg. Now I realize that a lot of guys riding the 500 get that or less, but I've been getting almost 60 for a long time and now it has really dropped off. The only other thing I've noticed is that I've had to use the choke more lately. Until some time in January, I rarely if ever pulled it all the way out, usually the first detente was all it needed, but lately I've had to put it on full choke for about 30-45 seconds and then drop back to the first detente for the next minute or two. Otherwise, everything is running fine. No problems maintaining highway speeds and I really can't tell any performance difference at all other than my mileage drop. I just put new plugs in in January after I first noticed the fuel mileage drop, and that didn't seem to make any difference. I also replaced the air filter after I started noticing this drop in mileage and I change my oil every 3,000 miles and it's not due for another 1,000 miles and the oil level is fine.

Anybody got any ideas?

Thanks for any input.

Burkbuilds

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Triangles
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Triangles » Mon Feb 14, 2011 2:36 pm

do they do winter gas down there in GA? In Ohio they have winter formula gas to supposedly help with fuel line freeze up and other cold weather issues that cars have. The winter formula gas gets worse mileage. This coupled with increased drag due to more dense cold air I usually have a drop off in winter mileage, maybe not quite as extreme as 8mpg but that's in the ball park.

- I'd check both front and back brakes you may have a brake dragging.
- I've never had a wheel bearing go bad, but I suppose that could be a possibility too.
- Hows the wear on your chain/sprockets. I've read that those usually only last 20-25K miles before needing replacement?
- You could have a burned valve, but that usually only happens when you have a valve that is tighter than spec. Do a compression test on the cylinders.
- Has it been colder lately? The colder it is the more choke you will need to use. The other day when it was 4F here I went for a ride and had to use full choke for 3-5 minutes before I could bump the choke down.
- It could be that heavy car tire you've got on there. A heavier tire = greater rotational mass which generally = worse gas mileage.
- Not sure what it could be but something out of adjustment with the carb?

Bikerbill might have some ideas. He put over 100k on his engine and had burned a valve because he neglected a valve adjustment for 24k miles.
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JWR
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby JWR » Mon Feb 14, 2011 2:46 pm

I am a firm believer of the K.I.S.S. method.

I don't have any ideas on the why, but I do know that the right hand is good for a 10-12 mpg difference.

I am sure you will figure this one out.

Best of luck.

burkbuilds
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby burkbuilds » Mon Feb 14, 2011 10:16 pm

Thanks for the replies guys. They do have winter formula gas down here, so that could be part of it. I do my valves every 6,000 miles so I don't think I've had any problems there, never found them tighter or looser than the outside spec and I always set them to mid specs. I do have over 30,000 miles on the chain and that could have something to do with it, although I recently had it checked by a good friend that's a former service manager for Suzuki and he said it was in mint condition and there's no discernible wear on the sprocket teeth other than a loss of paint on the friction surfaces. I suppose the chain could be "tight" in the pins and that could be causing resistance that I haven't noticed. I do have a new chain and sprockets, so maybe I'll go ahead and replace mine now and see if that makes a difference. I even placed a brand new sprocket on top of the rear sprocket when I had the wheel off in December and I couldn't tell any visible difference in the shape or size of the teeth. It has been relatively cold down here, but last night was in the 40's when I drove in and that isn't really all that cold, certainly no where near 4 degrees. I will check my rear drum brake, but I haven't noticed any feeling of drag or anything and the front brakes seem fine. I put new bearings in the wheels in early December and they should be good.
I think I'll add some carb cleaner to the fuel this week and see if that makes any difference. I'll pull the air filter out when I get home next weekend and see if it's gotten wet or something is restricting the flow, but it is less than a month old and should be in good shape. I guess it could be a combination of several things adding up to a big drop in mileage. Winter gas, carb needing cleaning, and maybe some resistance from the chain on top of that.

We are having a warming trend down here this week. It was in the mid 60's when I got off work this afternoon and the forecast by Friday is around 70 degrees, yahoo!

If you guys think of anything else that I should check please let me know, thanks again.

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Triangles
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Triangles » Tue Feb 15, 2011 10:56 am

when I use carb cleaner it usually hurts my mileage, but then I usually use a whole bottle meant for a car.
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fastpakr
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby fastpakr » Tue Feb 15, 2011 3:33 pm

The next time you do an oil change, send off a sample to a lab. They can give you all the data on it, including fuel contamination. Could be very useful in determining if you have a fuel system issue.
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burkbuilds
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby burkbuilds » Tue Feb 15, 2011 10:42 pm

That's a great idea fastpakr, I think I will do that. I added techron to the tank a few minutes ago (not the entire bottle though), maybe that will help as well.

burkbuilds
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby burkbuilds » Fri Feb 18, 2011 10:48 pm

I just got back in from Atlanta and after adding 5 oz of techron to my tank on Wednesday I managed to get 56 mpg on that tank of gas. That included about 45 miles around town before I hit the highway, so I think I mainly just had a dirty carb. I hope I'll grab a couple of more mpg's with this fresh tank now that the carb seems to be back to normal again. Thanks for everyone's input, I really appreciate it.

JWR
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby JWR » Fri Feb 18, 2011 11:30 pm

Glad you are getting back to normal.

I checked mine on very easy riding(easy for me) at almost 60 mpg.
The next tank was a little harder than normal at 48 mpg.

The way I ride I will probably be around 53 mpg.

shayden
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby shayden » Sun Jul 24, 2011 7:09 pm

My milege dropped about 10 % as I approached 7000 miles. I had the dealer do a tuneup (I had wanted to just change my oil but decided to be cautious). My milage is back up and the engine runs better. I think it was tight valves. The mechanic said the exhaust valves were too tight. Could also have been the plugs, maybe they were 5 years old. Bike runs much better at 70 to 75 now.

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Turbojoe
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Turbojoe » Fri Nov 11, 2011 10:51 pm

I'm fighting a mileage drop right now too and I'm convinced it's the gas as we move into winter. I'm only losing about 5-6 mpg from average though and not 10mpg like the OP. Hauling my fat, flabby (240lb) ass around is now giving me 46 mpg where I used to get 51-52 regularly. The bike is meticulously maintained and runs fantastic. Most of my ride is at 70+ mph and it's the same ride to work day in and day out. I've tried using 3 different stations and the results are always the same. There are no REAL gas available here in Phoenix. It's all minimum 10% ethanol but I'm thinking they've been bumping that up a bit lately. :evil:

I've been using the "Fuel Log" app for my Android phone since I got the bike in May and my highest mileage was 56.21 mpg. Total average since May is 48.75 but it keeps dropping to the 46 I'm getting now. I'm coming due for an oil change but the full 6,000 mile service was done at 7,800 miles because I wasn't certain the original owner did anything to the bike.

Every weekend she gets a shot of SeaFoam, a chain clean, lube and adjustment check and an air filter check and clean if even remotely dirty. 2 weeks ago I did a re-check of the carb synch using a manometer and all was still good. Not much more I can do other than go back to the Shell Rotella 15w40 from the Valvoline 20w50 motorcycle spec oil that I used on the last oil change. I can't see the minor viscosity change bringing the mileage down THAT much seeing as is doesn't get terribly cold here in the Phoenix area but what the heck, Rotella it is for the next oil change. I'll keep an eye on mileage after that to see if it improves.

Joe.
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Triangles
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Triangles » Mon Nov 14, 2011 9:50 am

FWIW I did see a measurable drop in mpg when I tried thicker viscosity oils when I had a '68 VW beetle. While obviously not a bike, the engine is more like a motorcycle engine than a regular car engine. It's that bump up to a 50 weight oil that will hurt mileage. I've always stuck to 10W40, but Ohio doesn't see the heat that AZ does. My cooling fan only came on once this past summer. I was kind of happy that it did so I knew it still worked! I've tried a 0W40 synthetic to help with winter mileage drop but it didn't seem to make any difference other than it started easier when below 20F or so.

Speaking of oil make sure whatever oil you use doesn't have the star burst logo that says "ENERGY CONSERVING" This logo means the oil has friction modifiers that while good for a car engine, will likely muck up our wet clutch. With that said, I've never seen a 10W40 oil labeled as such.
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Turbojoe
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Turbojoe » Tue Nov 15, 2011 2:22 pm

Because we've had such a huge temp drop here in Arizona I'm sure the heavier weight oil will have some affect in mileage. I'm coming due for an oil change in another 400 miles (3 weeks) and I'll be going back to the Rotella 15w40. It'll be interesting to see if it has an impact on mileage. I sure hope so.

An interesting side note...I had done a Rotella oil change shortly after I got the bike with 6400 miles. I was never happy with the clutch lockup so at 9400 miles I poured about 6 ounces of SeaFoam in the crankcase and rode it gently for about 30 miles. During the later stages of the ride the clutch started feeling better and better. I changed the oil with the Valvoline and clutch operation has stayed perfect. Because the Rotella and the Valvoline are both JASO motorcycle spec I have to guess the previous owner used regular energy conserving car oil and the clutch was about to possibly suffer some damage. The SeaFoam seems to have cleaned everything up and saved the day. (And the clutch). NEVER use oil not motorcycle JASO spec!

Joe
The nonsensical ravings of a lunatic mind.....

2004 Vulcan 500

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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Triangles » Tue Nov 15, 2011 11:21 pm

To clarify, it should be "JASO MA" As far as I know the JASO MA spec simply requires that the oil doesn't have the friction modifiers (ENERGY CONSERVING logo) harmful to a wet clutch on a motorcycle. NEVER use JASO MB in your motorcycle! It has the friction modifiers I've never seen this in the wild, but I've read of it's existence.

With all that said, I have only used car oil in my motorcycles for the past 24K miles or so and have never had an issue. The only thing I've looked out for was to avoid the ENERGY CONSERVING logo.
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Turbojoe
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Re: What might cause a 10 mpg drop in my fuel mileage

Postby Turbojoe » Wed Nov 16, 2011 3:55 am

Yeah, I probably should have been more specific about the JASO rating but I've never run across the MB myself. In a motorcycle specific oil I'm sure the only place to find it is a Harley shop or one of the few brands that still use a dry clutch. BMW? Not sure. It's still worth noting that JASO-MA is the one to look for and anything friction reducing or energy conserving is a big no-no in our bikes.

Joe
The nonsensical ravings of a lunatic mind.....

2004 Vulcan 500


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