24 MPG from my XX !!!?

[XXblitzkrieg]

First my XX never got great mileage best was like 35mpg. This winter I changed to a K&N airfilter and replaced the plugs (7500 miles on my 02). I must say I was underwhelmed at the performance difference and question if the bike was maybe slower. I realized I was getting only 120-140 miles per tank mixed highway and city....no 110+mph stuff either. I figured because it was colder weather 40-50 degrees that would account for the poor mileage. now it's been in the 80's and my last tank got me 24.3 mpg and only lasted 109 miles before reserve started to flash. My best guess is the plugs are shitty and defective or something.....anybody got any ideas? The bike seems to be running smooth and not missing or surging just maybe a bit rich and sluggish due to being rich...getting black soot on the tail pipe but not a huge amount (wouldn't pass a white glove inspection after cleaning and a subsequent 30min run)

Thanks, Brett

[Guest rockmeupto125]

Stock exhaust?

[XXblitzkrieg]

nope, erion slip-ons ....was getting 33-31 before with them on last season. tire pressure is good and nothing is dragging brake wise either. Chain is well lubed and in good shape...not to tight either. mileage seems to be getting progressively crappier with each few tanks of fuel...using mid grade 89 octane fuel.....One thing that I was thinking that I just checked was that I was sent IMR9C-9H plugs when I ordered IMR9A-9H difference being the A vs C for the 5th digit.....I phoned the parts company and they said it shouldn't matter......isn't that the heat range of the plug??? a A-H must be different than a C-H would this be the problem?

[BDAZ XX]

Thats about right, when I'm flogging it!

[XXblitzkrieg]

I'm going to be honest......I really haven't beeen driving much over 80 lately...just haven't had a safe chance to stretch the legs I usually keep revs between 4000 and 5200 RPMS just crusing around

[99Birdman]

I had been wondering about my mileage as well, since I was gettin high 20's when everyone else seemed to be getting mid 30's or better. The last week, I've conciously been shifting around 3500-4000 instead of my old 5500-7000. Guess what, I'm in the mid 30's now. Go figure. You might watch yourself and see if you started running the gears up higher lately even though your not doing high speed runs.

Also noticed I tended to let the bike warm up longer in the winter. Had a definite effect on mileage since I do a lot of short commutes.

[Northman]

NGK is very vague in what that digit means in the numbering system they use.

According to their chart, A,B, & C all mean "special design" in the firing end. It could be the cause of your problems, or it might be nothing.

Your bike calls for the IMR9A-9H's, so I'd tell the shop where you bought them that they sold you the wrong plugs, and they should supply proper ones to you. It's no problem for them to return the plugs as "defective", so they're just being stubborn pricks if they won't return them.

Have you removed the tank again, and checked for any disconnected vacuum lines or pinched hoses?

Was the IAT sensor left unplugged when you re-assembled?

I'd go over your installation again, and replace the plugs with the proper ones.

Let us know how you make out.

[gourmet]

Even flogging my bike hard I still manage about 20 26 mpg. Normal riding with some high end blasts I'm still in the 30 36 mpg range. Would plugs make that much of a difference to mileage? Possibly something not put back together correctly from the air filter install? I am not sure what but sounds funny to me.

Brian

[tgo63]

with abut 85% of highway riding, often in triple digits, I get regularly 39 to 40 mpg on my stock 2002.

[birdrunner]

Your bike calls for the IMR9A-9H's, so I'd tell the shop where you bought them that they sold you the wrong plugs, and they should supply proper ones to you. .

Pre 2001 models are supposed to use a CR9EHIX-9 according to NGK.ca's website : http://www.ngksparkplugs.ca/

Any idea what the difference is?

[Northman]

Pre 2001 models are supposed to use a CR9EHIX-9 according to NGK.ca's website : http://www.ngksparkplugs.ca/

Any idea what the difference is?

The CR9EHIX-9's are an update to the CR9EHVX-9's which were what the bike was originally equipped with. The "IX's" are iridium, and the "VX's" are platinum.

What I do know is that installing the IMR9A-9H's in your pre '01 will kill your mileage for some reason.

Been there, done that. :roll:

[birdrunner]

OK then, I guess I've been using the correct ones. Guess I'm gonna have ta go Big Bore to get the power I need.

[FloridaSilverBird]

I seem to be getting over 35 mpg when im not being conservative about my gas (using the 6000-8000 rpm range quite a bit, albeit just for getting up to speed). First time filling up the XX took about 4.6 gallons and I rode for about 160 miles, then filled it up again to about the same spot took about 4.25 gallons. So I figure 160/4.25=38 mpg.. Give or take some error..

Must have something to do with my 130 pound self?

[ZeeBeast]

This is kind of spooky. If the K&N is the culprit here, I sure as heck don't want one. Need a filter badly and was about to place a K&N in her. But if the milage is going to bottom out, I'll stay with stock. :?

[bartonmd]

I have a '97 with a K&N, stock pipes with punched baffles, and a Factory Pro jet kit and consistantly get 40-ish on my commute, and usually get 45 or so running corners doing "the pace." (or a hair less than 40 running hard, but I don't do long, high-speed runs, nor do I run REALLY hard)

Mike

Edit: You must also note that an internal combustion engine is a glorified air pump and a gas engine in particular is a glorified vaccum pump because you're throttling the air (you know.. intake manifold vaccum). Basically, the easiest way to get better mileage is to run a lower rpm with a higher throttle opening to get the same power (as long as you don't "chug" the engine). I usually run corners in 5th gear, or 4th if they're REALLY tight... This also does away with the dreaded mid-corner driveline lash...

Edit #2, I weigh 22lbs with my leathers on :wink:

[Guest rockmeupto125]

Don't forget to mention that you weigh about 22 pounds with your leathers on......

[EVLXX]

Sounds like a bad set of plugs to me as well.

One time I bought a new set of plugs, and spent the next week trying to figure out why my bike fekt slower.

I inspected the plugs a number of times always holding the electrodes up. That was the problem. The center electrode was broke from the factory, and when it was pointing electrode down, like it is in the motor, the center electrode would fall against the grounding electrode.

Now that being said.... maybe the ceramic has a crack in it. Or it could be something else.

... :?

[airborneXX]

My 97 with full Yosh exhaust, jet kit and stock air filter gets 42 mpg on the highway and 35 running it hard, and the plugs have 19,000 miles on them.

[Northman]

Basically, the easiest way to get better mileage is to run a lower rpm with a higher throttle opening to get the same power (as long as you don't "chug" the engine). I usually run corners in 5th gear, or 4th if they're REALLY tight... This also does away with the dreaded mid-corner driveline lash...

You mean "lug" the engine, right?

Your theory on fuel mileage I disagree with 100%. The best way to gain mileage is to decrease throttle opening, and keep vacuum at it's highest. That's why old timers have vacuum gauges installed in their motorhomes to save on fuel.

A lot of times, more rpm in a lower gear will result in better mileage as you have the throttle open less, and more vacuum.

Engines are fed fuel based on vacuum (lower vacuum = more fuel), so the more vacuum you can maintain, the better mileage you'll get.

[FiXXation]

As bartonmd stated, the vacuum pumping losses in a 4-cycle engine used to be significant enough to diminish fuel mileage back when a carburetor fed fuel based only on the volume of air going through the carburetor venturi. Running the engine at maximum load / minimum RPM, without preignition, was the most efficient way to get down the road (assuming a properly calibrated enrichment vacuum valve). Higher RPM, loaded or not, caused the ingestion of more air and equally more fuel.

However, I think with fuel injection maps, that's probably no longer true, as the fuel is metered according to many different inputs, and can be mapped to give efficiency at low-load, higher RPM conditions as well as lower RPM, higher load conditions.

[Northman]

As bartonmd stated, the vacuum pumping losses in a 4-cycle engine used to be significant enough to diminish fuel mileage back when a carburetor fed fuel based only on the volume of air going through the carburetor venturi.  Running the engine at maximum load / minimum RPM, without preignition, was the most efficient way to get down the road (assuming a properly calibrated enrichment vacuum valve).  Higher RPM, loaded or not, caused the ingestion of more air and equally more fuel.

However, I think with fuel injection maps, that's probably no longer true, as the fuel is metered according to many different inputs, and can be mapped to give efficiency at low-load, higher RPM conditions as well as lower RPM, higher load conditions.

Are you on crack?

Every fuel system made bases fuel delivery on engine load, which is a product of throttle opening. More throttle opening = more fuel.

If you were to build an engine strictly for mileage, you would tune the torque peak to exactly your cruising rpm resulting in the most efficiency.

A vehicle that pulls itself better will use less fuel.

[FiXXation]

Every fuel system made bases fuel delivery on engine load, which is a product of throttle opening. More throttle opening = more fuel.  

Welcome to the digital age. It ain't necessarily so any more.

Fuel is metered with input from the throttle position sensor as well as the ambient air temperature, engine temperature, oxygen sensor on catalyst models, barometric pressure via manifold vacuum at idle, PAIR valve position, and the computer map algorithm.

Actually, Northman, I was agreeing with you that with the aid of the fuel injection system, low load, higher RPMs and lower gears COULD give as good or better fuel efficiency. It depends on the FI mapping, as you say.

In the old days, the MPG champions crossing the country for fame and fortune used the high gears, low vacuum, low RPM method.

[Northman]

Fuel is metered with input from the throttle position sensor as well as the ambient air temperature, engine temperature, oxygen sensor on catalyst models, barometric pressure via manifold vacuum at idle, PAIR valve position, and the computer map algorithm.

On a mass airflow system (which is by far the most accurate), fuel is primarily calculated by the air volume entering the engine.

From there, it is fine tuned with the TPS, IAC, EGR POSITION, BARO, O2, etc.

On a speed density system (meaning no mass air sensor), fuel is primarily calculated by rpm & map sensor readings From there is again fine tuned with the above mentioned sensors as well as others, at least on a closed loop system.

Higher vacuum levels will result in higher mileage, regardless of what fuel system you use (except for diesel, you scrutinizing bastards in which case the opposite is true).

Running the engine at maximum load / minimum RPM, without preignition, was the most efficient way to get down the road (assuming a properly calibrated enrichment vacuum valve). Higher RPM, loaded or not, caused the ingestion of more air and equally more fuel.

Notice how I highlighted what you had previously written?

The power valve is held in the closed (lean) position by vacuum. When you lose vacuum, you open the jets more, and allow more fuel.

Go ahead and try this at home. Take a steep hill in your car in top gear. Take note of how far you need to push the throttle to maintain speed.

Now try it again in one gear lower. It will take significantly less throttle to maintain your speed in the same conditions.

Air only enters the engine through the throttle body/carburetor, right? Meaning less throttle opening = less air entering the engine, right?

Given an ideal ratio of 14.7:1 air:fuel, that would mean less air = less fuel.

An engine operating at a given load will have to make a directly porportionate amount of torque to maintain that load, regardless of the rpm in which you are trying to maintain it.

In other words, if you're trying to maintain 55mph on a steep hill @ 2000rpm with a full load, your engine will have to make a certain amount of torque to do the job.

Trying to maintain the same speed with the same load at a higher rpm (2500, for example), will require the same amount of torque, but the engine will be at a more efficient rpm requiring less throttle opening, and less air/fuel mixture to maintain that load.

Take a 4 cylinder car and tow a load with it (manual transmission preferred). You'll have to damn near floor it to maintain speed in high gear. Try it again in the next lower gear, you'll gain mileage & pull the load much easier with much less throttle.

Maybe back when cars redlined @ 3000 rpm & could idle @ 300rpm, the lower you kept rpm, the better mileage as long as you could maintain that speed with a high vacuum.

My original point was that lugging an engine killed mileage, and I stand by that.

Now, just to clarify we're on the same page here, I'm not talking about taking the same twisties Barton mentioned @ 8 or 9,000 rpm. I'm talking about taking them at a little more rpm than he mentioned, perhaps one gear lower. Gives you a little more rpm, and allows the engine to run more efficiently.

[bartonmd]

Chris,

The one thing you're missing is that, yes, the throttle is more open at lower rpm to make the same power, BUT the engine is also asking for less air, which means that it still is pulling in the same amount of air, and same amount of fuel... BUT the throttle is more open, which means less intake manifold vaccum.

On hi-po carb systems with a mechanical secondary, what you say is true, but that's why vaccum secondaries were invented... so the fuel/air ratio is always right (or as close as a carb can keep it).

The primary reason you end up getting worse mileage when leaving it in OD going up a hill, is because, especially on a FI engine in a car, they go open loop above something like 3/4 throttle, and as we know... open loop the computer says "this is how much air I have coming in at this temperature, engine is turning this fast, this is how much fuel I need, +20%, go."

Generally speaking though, a gas engine is, BY FAR, at it's most effecient when it's at WOT... and is more effecient at higher openings than at lower throttle openings. Example:

car 1 and car 2 are the same engine, same car, same everything.

It takes 25hp to move each car along at 60mph

car 1 is running 10% throttle at 5000rpm making 25hp

car 2 is running 40% throttle at 1500rpm making 25hp

cars 1 and 2 are using the same amount of air/fuel to make the same power to run the car at 60mph, but car 1 has to use more fuel/air to overcome the intake manifold vaccum created by the small throttle opening and the extra frictional losses.

car 2 is getting better mileage.

That is how it was explained to me when I worked at the engine control grad lab in college. Then they showed me on the engine they had on the test stand... Using Matlab SimuLink, you can see how much fuel and air is being put into the engine and how much power is coming out (because it was hooked up to an eddy current dyno).

This is also the reason the hybrid guys shift as follows:

WOT first

short shift to second

WOT second

short shift to 5th

WOT 5th up to speed

It also has to do with how much of the hybrid drive is being used on those cars, but those are the people who are the most concerned with fuel mileage. It is kind of off for the rest of us though, because if we go WOT, it goes WAY rich, and mileage goes to shit anyway... but these guys are closed loop all the time...

From here... http://www.insightcentral.net/KB/faq-effic...ml#acceleration

 

You'll get the best efficiency around town by accelerating with full throttle, and shifting up to the next gear quickly, before engine RPMs rise too high.  

There are two reason why this works. One is that the higher the gear, the lower the frictional losses. By getting to 5th quickly, the total number of engine revolutions is reduced, with a corresponding reduction in frictional losses. The second reason is pumping losses. This is the work done to force air past a partially closed throttle plate. The more closed the throttle is, the higher the losses. Accelerating quickly reduces throttle losses, because the throttle is open. In addition, engine speed is lower in fifth, so to generate the same amount of power, you have a larger throttle opening (and hence lower throttle losses) - this is another reason to get to higher gears as quickly as possible.  

By the way, I said specifically NOT to lug the engine (actually, I think I said "Chug" but you get the picture). Lugging the engine is hard on rods and bearings. I was simply saying to lower the revs a bit while still not chugging to get better mileage.

Mike

[Northman]

car 1 and car 2 are the same engine, same car, same everything.

It takes 25hp to move each car along at 60mph  

car 1 is running 10% throttle at 5000rpm making 25hp

car 2 is running 40% throttle at 1500rpm making 25hp

cars 1 and 2 are using the same amount of air/fuel to make the same power to run the car at 60mph, but car 1 has to use more fuel/air to overcome the intake manifold vaccum created by the small throttle opening and the extra frictional losses.

car 2 is getting better mileage.

In that case, yes, but I'm not talking about tripling the rpm to gain mileage.

I'm disagreeing with the theory that less vacuum is equated with better efficiency.

Now, don't confuse volumetric efficiency with mileage, either, which is what you're referring to with the "engines are most efficient at WOT theory.

Vacuum secondary carburetors were invented to maintain intake velocity. It doesn't matter whether it's two barrel, or 4 as far as intake vacuum goes.

FI engines go into open loop above 90% throttle, and they do run richer at WOT than they do during closed operation.

Running the engine at the lowest rpm it can reasonably do it's job in just makes sense, but lowering vacuum to gain mileage is totally wrong.

Don't the hybrid guys use full throttle to gain full benefit of the electric boost? That's one case where it makes sense.