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Discussion Starter #1
Ok so I ran a car tire for 20,000 miles. Didn't die, worked fine. Now I'm back on my Pilot road. Since the beginning this bike (unmodified) has averaged 43 mpg. Best ever 50mpg, worst 38 running hard.

2 weeks ago, changed rear tire, added new iridium plugs, cleaned air cleaner, replaced water pump O-ring.

Since then my mpg has severely dropped to 36mpg driving my normal droning commute. Tore it down and checked for leaks, nothing. Checked valve clearances -ok, carbs, nothing out of place. The only difference, other then tire and plugs, is the rubber plug on the airbox dropped out and I can't find it.

Will running it with the airbox not completely sealed cause this drop in mpg? I can't find anything else that may be causing this.

Oh, bike is almost at 50,000 miles now.
 

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I had to get one of those plugs from BikeBandit when I bought my bike as the PO had lost one too. I did it pretty quickly so didn't notice if that changed the milage. Does power feel the same? It doesn't have to be too much richer to really start dropping milage.
 

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Gee, when I run it hard I drop down to 28-29mpg..... and I also see the high 40s on the superslab, even getting a pinch over 50mpg now and then, but prolly averaging in the low 40s upper 30s...... I dont ride my ZX11 for mpg numbers.... if you are worried about mpg, buy another bike....

My D1 is well over 50k now....

Me thinks that running that Dozer rear tire for 20k has spoiled you on mpg, since you never could get on da power like a ZX11 needs to be....

Iridiums burn whatever gas you give them..... most likely you can back off the main jets just a bit....
 

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If you don't know where the airbox plug went, it's possible that it was ingested. Check cylinder compression and get the thing sealed properly.
 

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Discussion Starter #5
Ok the airbox plug was not ingested. I know I saw it fall on the concrete and roll away somewhere. I didn't get this bike for it's superior gas mileage. I keep a log of MPG for every tank to know when something isn't right. I know I haven't been riding the crap out of the bike but ....

Another fact - Ever since the MPG dropped nearly 10 points the bike has been running like a champ. These last few hundred miles it's been very strong. The car tire thing was just an experiment, it's over and I got what I wanted out of it. I know it works now and will be getting one on my touring bike.

So, my theory on the MPG is this. The ZX has always had a weak midrange-top end pull. It was probably due to gunk in the jets since this bike sat in the impound lot for 7 years with PO.

I'm thinking there could have been a clogged jet (or 2) and is now clear. I had cleaned the carbs out before but never did the pipe cleaner trick on the jets. Tire circumference may also play a small role. The Ct was about 2% taller which kept the RPM's a little lower on the slab.

This may be what is happening since...

1. Power is up
2. MPG is down to what I've read is normal for most other ZX11 owners
3. Nothing is is wrong

I don't know, maybe I'm way off. Just trying to find a reason but tear down the intakes this weekend.
 

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missing the air box plug could cause a lean condition.we all know that these bikes wont even idle right with the air box cover off so I would assume that any opening in the system would have an impact on performance. when they are lean, you compensate with a larger throttle opening for the same output ie you could use more fuel. I'd plug the hole and see.
Although Blaine is famous for the "if it aint broke right now,leave it alone" approach, (LOL)I would agree that a drop in mileage as large as you see means something though with all the shit going on with our fuel, I would'nt pass judgement on one tank.
 

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Discussion Starter #7
Has been 4 tanks so far. All averaging about 36mpg. I'll be duct-taping the hole. Lean + more throttle makes sense. When this started happening I had to adjust my idle way higher then normal just to keep the revs at 1000.
 

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If you must tear it down, pull the plugs..


Spark Plugs never lie.... if they are a light tan color, you are good to go....

and I have found the carbs on these bikes to be fairly touchy. Any kind of gunk in the jets would be very noticeable... Throw a can of Sea Foam thru a few tankfulls and call it good...
 

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been thinking........the average car tire in 205/17 or close weighs about 20lbs according th the tire rack. thats way more than a bike tire.That should mean that even with the larger diameter of the car tire, your mpg should have dropped unless all your riding was steady throttle,highway.It takes more power to accel the heavier tire.
I would plug the hole in the airbox and also check everything you touched while doing that service...air box sealed? hoses connected and not pinched ? ect.
Then there is also the possibility that now that your bike can function properly, you be usin that damn throttle more! :)
 

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Eww, don't put a car tire on any bike. You are severely crippling the handling and traction of the bike, and in an emergency that might be the difference between swerving and lowsiding the thing.

There are plenty of touring worthy tires that can get you well over 10k miles if you aren't riding aggressively. Hell, I am just running PP2CTs and there is over 5k (thats just what I put on them, plus the PO) on the back and I am sure I will get another 5-6k out of them.

But if you insist on trying to save money by using them, go nuts.

At any rate, its been two weeks. Two weeks is not enough of a sample size for mileage even with as much as I ride (50+ miles per day average) to call it accurate. If you are doing 43 average, then surely you have tanks that are lower or higher, and the fact that you mention it having more power (probably due to the cleaned air filter and new plugs) likely means you have been playing with that newfound power too.



And if you are looking for a nifty little tool to clean out carb pilot circuits, pick up a "tip cleaner" from the welding supply section of whatever local hardware store that has them. They are little packs of different sized wires that work perfectly to clear those holes out.
 

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...I keep a log of MPG for every tank to know when something isn't right. I know I haven't been riding the crap out of the bike but ....
Me too. MPG history can tell you lots about the bike's health when it changes dramatically without cause. You can have Fuelly.com keep track of your MPG results then compare them with other bikes of all makes and models.

As for your hypotheses, who knows. If the cleaning did jog something loose, MPG drops, but HP is improved? Oh well. That's a simple trade off we all live with. And it makes sense.
 

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Discussion Starter #12
Eww, don't put a car tire on any bike. You are severely crippling the handling and traction of the bike, and in an emergency that might be the difference between swerving and lowsiding the thing.

There are plenty of touring worthy tires that can get you well over 10k miles if you aren't riding aggressively. Hell, I am just running PP2CTs and there is over 5k (thats just what I put on them, plus the PO) on the back and I am sure I will get another 5-6k out of them.

But if you insist on trying to save money by using them, go nuts.

At any rate, its been two weeks. Two weeks is not enough of a sample size for mileage even with as much as I ride (50+ miles per day average) to call it accurate. If you are doing 43 average, then surely you have tanks that are lower or higher, and the fact that you mention it having more power (probably due to the cleaned air filter and new plugs) likely means you have been playing with that newfound power too.



And if you are looking for a nifty little tool to clean out carb pilot circuits, pick up a "tip cleaner" from the welding supply section of whatever local hardware store that has them. They are little packs of different sized wires that work perfectly to clear those holes out.
Yeah, not going to touch the car tire topic on this site anymore. But, I do agree with about the new found power enticing me to hit the throttle a little harder. My daily ride hardly changes. Same droning ride to/from work every day. Same traffic patterns, same stop lights, speeds, etc.. so when I fill up it's almost always the same 43-46 mpg. Lately it's been on the 43 side. I attribute the slight drop to winter blend gas.

So, when it suddenly dropped to 36 I flipped out. I'm sure it's a combination of things. Normal tire, missing airbox plug, new plugs, clean filter, and crisper throttle response causing me to yank it open a bit more.
 

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A normal bike tire should not be giving you lower mileage than a car tire, it should be the other way around. A motorcycle tire is going to have a lot smaller contact patch and likely will have lower rolling resistance, combined with weighing FAR less.

So I seriously doubt that has anything to do with it.
 

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Discussion Starter #14
alright, it looks as if this was a combination of things working together. This last tank I tried not to yank the throttle so much. Last night took it apart, pulled the plugs. Nice and tan. Plugged that hole with duct tape for now. Checked all lines, cables, vacuums and made sure everything fit back how its supposed to be. Checked tire pressure, rear was 29psi (must have gotten used to the funky feeling car tire to not notice this). Pumped air to spec. This morning filled the tank and hit the road. Just got home. Still haven't hit reserve and I'm at 190 miles. That's more like it. Still not where I was but much better. I'll fill up later to get exact mpg figure but i can tell it's at least 40mpg now.
 
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