really low gas milage, where to start looking?

I just got a '85 maxium. It typically runs well enough until of course I run out of gas. This is my first bike and I am hoping I can do most of the work my self, but where should I start looking? I'm getting about 25mpg at the moment. Every review of the 700 I have read indicates I should get far better. What is every one else getting?

 

my 750 gets about 40 mpg highway, i commute about 60 miles one way, full trip costs me around $9. My car gets about the same as your bike, definately not right. I run the high octane stuff, seems to do a bit better, but not that much. What shape are your carbs in? How many miles does your bike have?

 

I'm assuming here that if my carbs where in bad shape the bike would not start or run as smoothly as it does..... I have about 20,000 miles on the odometer and I have been running with regular gasoline for the almost 200 miles I have put on the bike. Two asides, the bike did sit in my garage for about 4 months after I took possession of it before I started riding it. Also the 'your about to run out of fuel' light does not function. (jackncoke: I have a civic and it gets far better gas mileage than my bike!)

 

so you've only ridden it 200miles and you're worrying about fuel economy? Maybe you've got old fuel left in the tank, give it a couple of tnaks full before you worry too much about it

 

Sounds like a carb problem.
No issues other than milage...ay?
Idle is running normally?
WAS there old gas for 4 months?

Could just try the good old seafoam...Works just like snake oil!!!
...but less smelly

 

Check the air filter. If it dirty, blow it clean with compressed air from the inside out or strong vacuum on the outside. When clean you should see light though the filter. Welcome to the site alot of information from fine folks here.

 

The outta fuel light is the reserve, I dont even look at that gauge.
It is worthless, and might lead you down a dark alley.

 

As best as you can ... describe how the Bike is running.

Idle?
Sitting at a light?
Taking-off from a Red Light?
Highway?
What happens when you are in a lower (2nd or 3rd) gear and need to put the power-on to accelerate?

 

One thing that can cause poor mileage is brakes dragging, maybe the front brakes are not releasing all the way?! (due to the relief in the master cylinder getting plugged)

Ride that bike without touching the front brake for about 10 miles and then see if the front rotor is hot. (be careful not to get burned)

I have a 700N and get between 38 - 42 mpg
temperature and humidity are factors but not so much as you are looking at.

Fuel grade could play a role in this area too but I oNLY run Regular Unleaded in my bike, I have tried higher octanes but it does just as well on Regular.
Definatly install an inline fuel filter if you dont have one yet.

 

In order to be getting that BAD Fuel Economy ... Gas has to Pouring IN ... or, Pouring OUT.

If the Petcock isn't leaking by and the Oil isn't contaminated ... Do an Exhaust Pipe read.
Wipe the end ot the inside of the Exhaust Silencer and see if it Pitch Black and heavily accumulated.

Then, do a PLUG READ. Pull the Plugs and line them up 1-2-3-4 .. show us a photo close-up of the 4 Ceramic Electrode Ends of the Plugs.

I'm betting your Exhaust is sooty and the Plugs are on the hair edge of being fouled ... black.

You MUST be running RICH if there is NO Leak.
Be prepared to need to do a Diaphragm Piston Bores re-finishing and / or a re-setting of the Pilot Mixture Screws.

Bottom Line ...

You're wasting gas.
If there's NO Leak ... you are using almost twice as much Gas as you need to be.

The Gas goes in the Tank.
If it ain't leaking ...
Next stop is the Carbs ...
They must be needing some kind of Cleaning related -- Tuning related work.
To be running that RICH without "Wet Fouling" the Plugs has got me scratching the top of my rapidly going bald head.

Where's all that gas going?

That's a LOT of gas getting wasted, lost, burned or leaked-out.

Get the pix of them plugs on here and let's have a look at them!

 

Got me wondering because he says it runs sweet......... (1st post)

 

I would guesstimate that the vast majority of the Membership isn't Dialed-In right on-the-money.

Many people are very happy to have a Mid-range on Up and be able to ride.
Far too many riders are "Red-Light-Rever's" ... needing to keep the bike from stalling out at a light or needing to get the bike "Off-Idle" to get out-of-the-hole.

You shouldn't be happy with the way your bike is running unless you can let-go of the throttle grip and have the Bike Idle as steady as the Atomic Clock.

Wait for Red Lights with your hand in your rear pockets ... the bike Purring beneath you at 950 to a thousand rev's and have nothing to do but let out the clutch and put the power on to get away from the light.

You should have a "Double-Oh-X-J" License to TWEAK if you've been here and kept-up with the Tuning Related Posts.

The only way to get a bike running that good is to get-on with the job of Tuning it without making any compromise.

Once you get your Bike into the Zone of Fine-tuned ...
You turn the Key and Hit the Button and it Starts.
The Enrichment Circuit is lubes so you can orchestrate the Enrichment.
It's not an ON-OFF thing.
You can pull-up to a light and blow two-handed kisses to the people wanting to ride a bike that sounds that good.
You ain't the last guy to the next light because you GOT Throttle Control.

Sometimes your the first guy to the next light. That really pisses-off the guys on overpriced, loud, American Bikes.

Your bike is so well tuned ... that you don't hesitate to jump-on and go to Duncan Donuts ... or,

To go visit an old friend who lives three or four hours away!

 

Rick you spelled it out that tuned XJ is an awsome thing to hear and experience.

I just wondered why he lost so much economy, seems he must be runnung rich when at higher speeds. Dont think the he would use all that much at an idle!?

Leaky petcock could do it too, if all that gas is going into the oil!?

Another thing is to put the bike on the centerstand and try to turn that front wheel and see if there is any drag. Then try the back wheel.

 

Bad plugs and or wires as well... Not getting nough spark can cause it. Air filter is a very good idea as well.

 

If AdamLD is running that rich, I'd love to be behind him at dusk when he's downshifting heavily. That thing probably shoots flames out the tail pipes!

Awesome! (but bad on fuel mileage.)

 

Rick - beating a Hardly to the next red light is not a sign of a dialed-in XJ. It's a sign that you you are riding a motorcycle NOT manufactured in Milwaukee.

 

Ok, I just finished putting in new plugs! I pulled them out this morning and they where BLACK. Also they where NGK bR8es not the bP8es that the book calls for. I'm not sure on the difference, could any one who knows please take me to school on them? I checked the oil filter and it didn't look so hot even after blowing it out with my compressor, so a new one is on order. Then I put some 44k into the tank - Ive just found it to work really well in my car, and I didn't want to have to run into the autoshop a thrid time today for seafoam. I will try make time this evening to ride for a while and see if the front rotor is warm or hot from those breaks dragging. There is a little friction or drag on the rear wheel, but I am not sure how free spinning it should be. I can spin it easily, but its not like the rear wheel of my bicycle.
OK, all the other questions:
-petcock isn't leaking.
-the fuel was 4+ months old, but I had mixed stabil in when i stored the bike (and let it run through the motor a bit)
-The bike mostly starts fine, some times it helps to roll back the throttle a bit as I hold the start button (with the choke all the way open). With the choke all the way open the bike idles at around 4k rpm's. That being said, a few times I have experienced that even with the choke all the way open the bike idles initially at 1k rpm, then I have to roll the throttle back to 4-6k or so once or twice and and then I can push the choke all the way off and be at around 1k again.
-idles fine at lights
- I have plenty of power in all the gears for acceleration (so much so the first few times on the bike it was rather shocking - I used to have a vespa in college) & I can also go slowly or any other speed in between.

Thanks to every one who responded so far, there has been a ton of information and responses! I had a blast trying to sort through it all this morning and working on the bike!

(it does not shoot flames out the tail pipe)

 

You might want to replace the plug wires as well....

 

Cant replace just the plug wires unless you have an aftermarket coil, or unless you get those spark plug wire splicers, not sure if they would be worth the money/effort though. Probably wouldnt hurt to change the plug caps though and save up for an aftermarket coils.

 

I had no idea, well there go's my idea!

 

Now you have to determine if the Diaphragm Pistons are too slow coming down or the Pilot Mixture Screws are set-up too Rich.

I have a sneaking suspicion that you are going to have a combination of both.

Reduce the Pilot Mixture Screws ... (Turn them IN about the width of a Nickel)

Don't strip the heads off the screws ... Make sure you have a screwdriver that fits the slot with NO end-play!

 

OK, sounds like stuff I can tackle this weekend. Is there already a thread that addresses doing all this? What should I be looking/feeling/listening for as I adjust the Pilot Mixture Screws? And where are they? Same two questions about the Diaphragm Pistons.
-Adam

 

Adam, should you find that you do need to change out those plugwires, check out Daves XJ Page.
I'd send a link but I cant go to html sites out here at work. (blocked)
He has a very informative article there about changing plug wires.

You can change out plug wires but you will need to Dremel the coil housing and then reseal it with epoxy.

I'd drain out that old gas and put fresh gas in and Seafoam and run it around for about a weekend (1/2 tank or more) then I'd go for a highway speed ride and then pull those plugs and see what they look like then.
1st, if you haven't already... put on an inline fuel filter.

Good Luck

 

Oops, sorry forgot to mention: there is an inline fuel filter.

 

Adam,

I am watching this post very intently as my bike is NOT running on the far side of good and miles away from dialed in. I am going to check my air filter when I get home, but I hope that you using a compressor on your old oil filter was a joke as it would be very messy otherwise. I am commuting to work about 12-15 blocks depending on construction and I also have to use the choke to get it to warm up so it's running around 4K when it warms up, but on most days, the bike wants to quit at every stop sign until I am almost at work. Then when it does get warm it sits up around 1500 -2K. Not what a dialed in bike is described as! After my air filter I will be checking my plugs also. I mostly fear that a commute that rarely gets me into 3rd gear is just going to be hell on gas mileage. And I don't see the flames, but I bet I could attribute some of the soot on my pipes to that.

 

I've got some more info on the plugs,,,I happen to have b8es in the garage for the atv's...an did a comparison with the bpr8es I have also using the chart the p is a projected insulator an the tip is going to be closer to the piston, not sure what the results will be with it farther away but do know it's way safer than getting closer than stock to the piston.
the r is also not called for an some bikes don't like the added resistance,,,
but if somebody put nonresistor plug caps on then it would call for an r I believe,,,,have you checked the coils resistance yet
I beleive returning to the stock parts will help the boys help you.

 

The Diaphragm Pistons are covered by the Top Cover on the Carb. You remove four screws and lift away the top and the return spring.

They need to travel up and down in their bores without binding on oxidation on the cylinder walls.

The Pilot Mixture Screws are on the top, front, just below the top cover and to the side of the enrichment circuit valve. There's a hole with the top of the screw showing or a brass plug in the hole to be removed for access to the screws. The small hole plugs need to drilled-out and removed.

Careful with the drill because the head of the screw is just under the plug cap ans the top of the screw is soft brass and will be damaged if the drill bit contacts the top of the screw.

 

The NGK has a splendid part number breakout chart for your use. The R means resistor as dburnettesr pointed out which brings me to another point, your coils are meant to operate with a finite resistance built in. The addition of the resistor plugs can degrade your spark strength, leading to harder starting and less efficient power. Get the right plugs in there.
I would work out the fuel and spark plug issues before I would worry about the coil as a suspect. Check the coil primary and secondary resistances (2-3 ohms primary, 11K more or less for the secondary). If they are out of tolerance on the primary, don't waste the time rebuilding them. Coil restoration is possible for a very low investment ($20 for plug wire and a tube of JB Weld, be sure to get the copper core, not the graphite).
Best of luck!