Has anyone had success correcting high fuel consumption?

I'm back at it with my 85 XJ700N which is getting only about 31 mpg in town and 35 on the road at a steady 60 mph. The bike has approx 11500 miles on it, compression is in the 135-142 range, and as far as I can tell everything is stock except for the UNI foam air filter. I've done all the normal things and before I start over, I would like to have any input from folks that have been able to correct high fuel consumption problems. Chacal has the OEM paper air filter, but even he thinks that will not solve the problem, so I'm going to wait on that. I've seen many 700 riders state that they are getting between 45-50 mpg on the road, and I'd be very happy with anything approaching 45. Any suggestion or story will be appreciated.

 

What colour are your spark plugs if you do a plug chop at cruising speed? (need to warm engine to operating temp, then fit new plugs, then accelerate to cruising speed and hold it steady for a few seconds. Then simultaneously hit the kill switch & pull the clutch & pull to the side of the road & check plugs)

Obviously make sure you're safe to do this, nobody going to rear end you or pull you for erratic riding etc... The idea is to judge fuel mixture at a specific point in the bikes running, hence the need for new un-tainted plugs & to cut the motor and not allow it to coast down or idle before checking plugs.

Also, when you say everything's stock have you verified all carb jets & needles are correct/not worn or damaged and that float heights are wet set correctly?

 

I've been dealing with some high fuel consumption recently myself. In addition to the plug chop.... I would recommend going over your entire fuel system to be sure that you aren't leaking somewhere or dumping gas slowly in your crankcase. I had a float set a bit off and was dumping a little bit of fuel while running.

The plug chop will tell you the most information, but you should also check all the "stupid" stuff like cracked lines, just to rule that stuff out too.

 

I could have sworn I suggested going back to the stock paper filter a long time back, in one of your previous threads on the subject.

Did we also resolve the "shifting too soon/lugging the engine" possibility?

 

what are the optimum shift points for gas mileage BTW? :roll: Im a newb

 

Pull your Plugs.
Line 'em up ... 1, 2, 3 & 4
Take a pic of the business-ends.
Let's see how you are running.

 

Tabaka, I pulled mine up from mid 40's to above 50mpg, by valve adj, air box stock and cleaned, carb clean & synch, E3 plugs, several early oil changes with 20w50, brake overhaul, electrical contacts all cleaned, new tires 29psi, bearings repacked, and etOH free gas.

I keep thinking the key to your dilemma is in your pilot jet(s). One or more must somehow be dumping too much fuel.

High enough that your throttle response transfers to the rear wheel without lugging or a delay. Does that mean wind it out? No but believe it or not you will achieve better mpg if you keep the engine running near the 'sweet spot' or where torque is maximized.

But if you're not under load, i.e. not accelerating, fighting drag (over 40mph), or climbing a hill it's ok to rev down. Then if you're going back under load before stopping downshift until you get back to the SS.

 

You need to revisit the tuning process. Valve adjustment, float levels and carb tuning are critical for proper fuel mileage and preformance. Yes you should be getting better than that, my XJ11 does a little better than what you are currently getting.
Your riding habbits also have a effect on mileage. I have seen "lugging " the engine mentioned. Keep the PRMs up.

 

tabaka
If all of the above suggestions don't lead to significant fuel consumption improvement, consider loosing weight, lol!

On a more serious note, my mechanic told me he noticed a fair difference (close to 10%) in fuel consumption depending on the gas station. Price was the same at both stations. HE said gas is probably not the same quality.

 

I got a little burned out on this machine a couple of months ago, and took on another project to give my self some time to think about all the issues and recharge. I got a price on the paper filter from Chacal, but even he suggested that he didn't think that was the problem. So I've decided to start over this weekend. The first thing will be a plug chop, and I'll post pictures. Then I'm going to recheck the valves and do a carb sync and colortune. I'm running 10-40 Amsoil, and I'm going to fill up with non-ethonol gas and see what happens. If I still have problems, I'll pull the carbs and check everything under a microscope if necessary and get the paper filter. My brakes are new and not dragging and the wheels turn freely. I seem to have a good spark but don't have any way of checking it. The plugs are new and are the ones recommended in the manual. Thanks for all the suggestions so far.

 

Check your tire pressure too, although I'm sure you have already thought of it.

 

the first two pictures were taken after a 65 mph 8 mile chop. The last two pictures were taken after a 5 minute idle. The pictures are a little darker than I remember them. They don't look that rich to me, but I don't have a lot of experience reading plugs. What do you think?

 

I'd say they look on the black side... Have you got a Haynes manual? they have a plug reading chart, or possibly there's one online somewhere I'm not sure...

 

Rich, although it depends how much darker they are than what you remember then to be. "Light lunch bag brown" is just about right.

 

Hi len, could you have a look at the oil burning/inconsistent idle thread please? Wondering if you have the part the guy would need?

Cheers

Sorry tabaka [/hijack]

 

You're "In-the-zone"

That coloration is ** Safe **
Not too Rich -- Not too Lean

From there, ... you can TWEAK.
A TWEAK means you don't do much.
If a stopwatch shows 60-seconds, ... 15-seconds would be a Quarter-turn.

From where you are now, ... you are within +8•••••••0•••••••8-
Plus or Minus 8-Seconds from Finely-tuned.
You're good right there.

Run a tad Leaner and you'll intensify the "Burn"
A smidge Richer and you'll have a "Cooler" burn -- for long-haul running.

If you go Lean, ... you have to be very careful to NOT go Critically Lean.
If you go too Lean you can suffer a catastrophic failure.
Melting through the Piston.

Your adjustments from where you are now are a matter of FEEL.
Don't "Turn" the Pilot Screw.
Barely move it.
Tweak.
You can Tweak one Hole and leave the others alone.
Go by each Plugs "Read"

Lots of Old-school Tuners would look at those pics and give you an A.

Just be careful.
Real careful.
Because there is a temptation to Tweak ... Lean.
You wrist-open and the Bike takes-off like a bat-out-of-hell.
But an Aluminum Air-Cooled Engine can't handle the heat.

 

Thanks. I like the idea of tweaking one plug and comparing. I'll try that over the next few days and probably post some comparison pictures.

 

IMHO you're way too rich, pull any plug out of a late model Fuel injected vehicle and they won't look near that sooty/dark.

 

It's not a late model fuel injected car, it's a 30-year old Jap four.

HOWEVER:

You are running rich. But VERY EVENLY. Which means you've done good work. Don't tweak one carb. Whatever it is, it's common to all 4.

Now PLEASE change the bloody air filter back to stock.

Then get some new plugs and repeat the above processes.

Did we bet $5 yet?

 

Haven't bet yet--but what are you proposing? :lol:

 

You don't Tweak one Plug and compare.

You Tweak one Hole IF it needs it.



I've tried Tweaking my 4-Hole.
It looks like I have a bad Valve Seal.

 

:lol: sorry, that looked 50 shades of wrong when I first glanced through the thread! 8O

I'd tend to agree with that, you've obviously got everything even across the board so I'd change that filter first as its the cheapest/easiest thing to do,

then *if that doesn't cure it* I'd be looking at float heights (not as likely inaccuracy in your setting technique as much as innacurate reference point or height specs used) and finally, at replacing main/idle jets with stock (even if they are, in case they were enlarged somehow)

 

Ok--I replaced the Uni foam filter with a Yamaha paper air filter--thanks Chacal--tightened the pilot screws about 1/2 of thinness of a dime, filled it up with non-ethanol 89 octane gas and took a 20 mile ride and checked the plugs.
1. the bike is running richer than before--plugs are almost sooty.
2. If I engage the clutch and go to idle, it almost cuts off, and actually did a couple of times.
When I wet set the floats--this bike calls for 1 mm +/- 1--I purposely set it at 2. The pilot screws are somewhere between 1 1/2 and 1 3/4.
So my question is what is causing the almost stalling, and how far can I reasonably close the pilot screws? Or anything else you think I need to check.

 

OK I'm all for bad (enlarged or non stock) jets/needles now, otherwise I'm out of ideas if everything else is stock and all your float/pilot adjustments are on the lean side of spec :?

Anyone else got anything to add that I'm missing here? (tired, so, yes I am making excuses!

 

Altered, or non-stock, jetting seems entirely plausible.

 

The jets have the correct number on them, and I tried to measure them with the smooth end of a drill set and the mains appear to be correct. I didn't have anything small enough for the pilot jets. The needles also appear to be the correct ones. Any better way to measure the jets?

 

I first saw this online spark plug color tutorial on this site and still have it bookmarked: http://forums.bimmerforums.com/forum/sh ... ing-Thread

 

I forget now if this has been covered, but another thing to consider as well as enlarged jets.

Does the bike have good compression (what figures do you have?) and does it use any oil at all/how much?

 

are your jets in the right spot? that was my problem?

 

compression is in upper 130's and lower 140's. The jets are numbered correctly and in the correct place. I checked the mains with a drill set, but will check again if I have to go back into the carbs. For the time being I'm going to just continue to close the pilot screws and see what happens.

 

Just for shidds and grins, ...
Look at the AIR Jets below the Diaphragm Rubber.
(There may be a Baffle to remove to inspect them.)

AIR Jets are "Opposite" from FUEL Jets.
The Pilot AIR Jet is LARGE: [O]
The Main AIR Jet is SMALL: [o]

Be sure that they are correctly placed.
Three are three (3) threaded ports.
1) Pilot AIR: LARGE
2) Main AIR: Small
3) Threaded Hole for Baffle Fastener (If present)

 

So you wet-set the fuel levels at 2mm below the line?

It's "dumping" fuel somehow, and doing it evenly across all 4.

I'm beginning to suspect the enrichment plungers/mechanism.

 

I'll check them again just in case. I noticed that your picture mentions covering the screw hole. I know the baffle is not in any of them. Should I plug them?

 

I think "cover threaded hole" just means it's a threaded hole for the cover?

 

The plungers are seated and the forks are loose so they aren't keeping them open. Just for the h--- of it, last week I got it to a warm idle and then opened each plunger one at a time with a small screw driver and it definitely caused the idle to increase and each plug to soot up. How would I check this circuit if I have to remove the carbs again.?

 

The Threaded Hole for the Baffles Fastener is a Blind Hole.

 

Wife bought a horse, then a used trailer. So, I've been rebuilding a horse trailer for the last few weeks. Rode the bike about 10 miles today and checked the plugs--serious soot. Pulled out the colortune and adjusted the pilot screws to initial blue. All the pilot screws are now set at about one turn open plus or minus a bit. I read somewhere on the internet that if the pilot screws required less than 1 turn then smaller jets were required. The XJ700N has 36.5 pilot jets so that's about as small as they get. Before going back into the carbs I'm going to ride the bike and see how the plugs look and how it runs. This seems to be screaming high fuel in the bowls or perhaps leaking enrichment circuit. The enrichment plungers and the seats appeared to be smooth and shiny, and they are definitely not being held open. When I last set the floats I set them at 2 mm. The manual calls for 1mm =/- 1. Do you think that pilot screw settings this low could actually be ok?

 

The Pilot Screws regulate AIR.
Some Old-timers call them "Air Screws".

As you adjust the Air Screws OUT; more Air is allowed to pass into the Combustion Chamber.
This AIR ::: Siphons ::: Fuel from the Pilot Fuel Jet Supply.

Once the Air Screw is ::: Fully Open ::: the Quantity of Fuel is regulated by the Pilot Fuel Jet's metering of Fuel to the Passages.

Bench Sync the Rack with a FEELER that will let the Butterfly's be closed.
(3X5 Card Strips, Business Card Strips ... Strips of 35mm Negatives)

With the Throttles Closed; ColorTune for IDLE.
Blue.
Once you have each Hole >> Blue >> the Bike should Idle like a Sewing Machine. Nice and steady.

Tweak each Air Screw OUT until the BLUE just starts to fade-out with additional Richness.
Once you arrive at IDLE + sufficient Supplemental Richness to support NO Hesitation upon opening the Throttles, ... you should be within the width of a Nickel or Dime away from being spot-on.

 

Just a thought, if you are judging jets by their numbers, make sure they are not drilled out from original.

 

I did the bench sync with the card strips, then did a running sync. I have the idle setting just into the blue, but I'm just a little concerned about the pilot screws being open only about 1 turn. But it definitely isn't lean at idle.

 

I checked them once, but didn't have anything small enough for the pilot jet, so if I go back in I'll make sure I check them, even if I have to take them to a machine shop.

 

Well, I bought a parts bike and discovered that I had '86 carbs on my 85 bike. Still Hitachi 33's, but slightly different. Anyway, I cleaned the 85 carbs and put them on the bike and made an initial pilot screw adjustment. They are out anywhere between slightly less than 2 to slightly more than 3. The plugs are still a little dark, but the bike runs better than it ever has, and the initial check of mpg has added approx 4 mpg to about 39. Hopefully, when I get the pilot screws set correctly I'll be over 40 mpg or better.

 

Once you get dialed-in, ... the mpg's won't significantly improve.

The two main factors for gas mileage are:
• The overall "Health" of the Engine.
• How you ride.

 

Need to check your pilot fuel jets. The PO "drilled out" the 40s to a larger size b/c he had a 4 into 1 aftermarket exhaust. I could not get my seca 750 to not have sooty plugs until I swapped in pilot fuel jets from a spare rack of carbs. Here is a previous link describing the same problem I had. Worth a shot at ruling out drilled out jets still marked with original size.

http://xjbikes.com/Forums/viewtopic/t=31550.html

 

have you checked the microscopic o rings, washers, + springs under your pilot screws to be sure that they are good and seated properly?

Also, just for comparison, I'm getting around 35 MPG on my S. I live in between 5K and 8k.

Here's a random thought for your... reading your thread, I know you have both S (no vac port)and N (vac port) carbs, are the right carbs on the bike?

Here's another random thought for you..... are your coils original? My gas mileage (and engine response) improved slightly when I upgraded to dyna coils. Most likely from poor spark/inefficient burn

 

When I bought the bike it came with the non-port vac carbs which I am told are 86 or "S" carbs. I just replaced them with the vac port carbs (85 or "N") that came on the parts bike I bought. The o-rings are almost new and in good shape. Since I had just installed metal float seats and needles in the '86 carbs I put them in the '85 carb before installing. Other than that I cleaned them and used them as they came. Before buying the parts bike I had pretty much decided to change out the pilot jets in the '86 carbs since the po had installed a UNI foam filter which flows a lot more air and I figured that maybe he had drilled them. Besides, I had pretty much ruled out everything else. I like stock and so I'm running a stock filter now.

 

so we seem to be at pretty much the same in fuel consumption now.... I don't know what else to look at. I'd like to increase mine a bit more too. I haven't heard too many people claim the 45-50 figure though.... but I'd love to be in that range with such a tiny tank....

 

The small tank is a problem getting only 35 mpg. Stopping for gas all the time. I wish there was a larger tank available.

 

I think I have this bike as close to perfect as I can get it. I checked the float levels again and one was out a tad so I now have them all set at 2 mm. The range for my bike is 1 mm =/- 1. I then used the color tune plug and closed the pilots until I got some white and the idle slowed. I then opened the pilots until I got a good blue flame and a smooth idle. I then put in new plugs and tweaked the pilots until I got the plugs shown below. Since these pictures were taken I have tweaked the 1, 2, 4 pilot screws about the width of a dime, and the 3 pilot about twice that. The pilots are set between 1 and 2, and I think about 1 1/2 and the plugs look great. I am now averaging about 41 mpg in mixed--mostly town-- driving. Today I took a 73 mile road trip and used 1.7 gal, for about 43 mpg. A friend that rode with me on his 2008 Honda clocked 76 miles for the trip. If his miles are correct then I got 44.7 mpg, but even if I split the difference it's still almost 44 mph. The bike starts and runs great and I'm satisfied.

Before I had been tweaking the pilots from a rich setting and it was hard to really read the plugs since they had already been blackened in the rich setting. Starting from a lean setting with new plugs allowed me to easily read the plugs and tweak them to the current setting.

 

44 MPG is good and your plugs look fantastic. I typically get 37 in town and 50 on long stretches of highway. Well done.