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Discussion Starter #1
I am having TERRIBLE fuel economy on my 636. I've had to fill up twice in ~85 miles.

The bike has a had a sprocket change, -1 +2. No aftermarket electronics. FMF exhaust.

When I'm riding and I come to a stop with the clutch in, the bike will randomly die sometimes. Also when I rev it at WOT it'll stop for a quick sec at 4k, then go to redline. Then it spews black smoke and sometimes pops flames.

Any ideas? Am I running too rich/lean? If so, what do I do?
 

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that sounds like you're running really rich. another thing you can do is start your bike and stick your hand at the end of the exhaust and see if you get any droplets and if you do, take a whiff. if it smells like fuel then you're running rich.

but your other symptoms are already kind of leading me to you running on the rich side.

the 03/04 Zx6R's are fuel injected so you very well could have a faulty injector that is either injecting to much fuel or sticking open.

pull your plugs and see what they look like as they can give an indication on whats going on and if one doesn't match the others then that can pinpoint your problem injector if in-fact you're having injector problems.
 

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I am having TERRIBLE fuel economy on my 636. I've had to fill up twice in ~85 miles.

The bike has a had a sprocket change, -1 +2. No aftermarket electronics. FMF exhaust.

When I'm riding and I come to a stop with the clutch in, the bike will randomly die sometimes. Also when I rev it at WOT it'll stop for a quick sec at 4k, then go to redline. Then it spews black smoke and sometimes pops flames.

Any ideas? Am I running too rich/lean? If so, what do I do?
First of all, how long have you owned the bike?

Second, has this changed since you have owned it?

How many miles on the bike? When was it last tuned up? Valve adjustment? Spark plugs?
 

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Discussion Starter #4 (Edited)
Yeah, I'm getting a bit of soot when sticking my hand behind the exhaust. And I recently did do the plugs since it wouldn't start before. They were fouled to shit.

I've owned the bike for maybe a week, and it's been like this since I got it. The bike has 26k and I don't know the last time the previous owner serviced it. He changed the pistons and transmission since he was a motorcycle tech.

Should I take it in for service after I check the plugs again? What causes a bike to run rich?
 

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I wouldn't put too much faith in what the previous owner did or didn't do. But most likely the later especially if he's a motorcycle tech who failed to change plugs but claimed to do major internal work??? I'd suggest start with what maint you can do and seek help on how-to on the rest if you're comfy with it.
 

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I dunno if that's a straight fueling issue. 85 miles on 2 tanks? I don't care how rich the fuel is running, that's way low. With the smoke and the flames shooting out, you must have one or even a few cylinders that are not burning the fuel inside the cylinder, which points to a spark plug problem. You need to check the spark plugs to make sure each of them is sparking and determine from there what the issue is (maybe bad stick coils)

Could be blown exhaust valves also which would be the result of the valves not being properly adjusted. When they get too tight from neglect, they push up against the other moving engine parts and eventually may break.

But honestly, a bike with 26k that's had and having this many issues, you're in for a rough ownership. That bikes had MAJOR issues and 26k is nothing on a bike. I mean replacing pistons and a transmission at 26k is really bad.
 

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Discussion Starter #7 (Edited)
He's a nice guy and actually gave me all the parts that were swapped out so I do believe him. Plus his garage is filled with bikes and he was rebuilding a CB750.

But the plugs probably failed the first time when it was in my possession, due to it running so rich. When the owner rode it to my house, it fired up fine, then the next few times I tried, it wouldn't start.

I already changed the plugs and the oil, but I don't know how to diagnose why its running so rich.

And how do I check to see if each plug is sparking? About how much does a valve clearance cost as well?
 

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You have to do a resistance test on the stick coils. See the service manual how to. You can YouTube videos for extra guidance.

Valve clearance check varies widely depending. From 200-700 I've heard various members claim to pay. But if it's not a spark and it's a broken exhaust valve that's causing the fuel air to not compress and shoot out into your exhaust where it burns up, that's going to be much more expensive.

You know the guy better than I do but if he did the bear minimum to get the bike back running and didn't check valve clearances after he installed new Pistons, it's possible the valves started hitting off of the piston heads and broke. Most likely it would be an exhaust valve. Which would go right in line with what's happening with fuel burning up in the exhaust.

And I gotta say once again, you're talking about getting a quarter or a third of the normal gas mileage of this bike. I just don't see how it's possible to run that rich that you're getting such low fuel mileage. I mean I guess anything possible but anything running that rich to the point of essentially running ~10 miles per gallon probably wouldn't be running at all.
 

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Discussion Starter #9
A valve clearance check is definitely on my list of to-dos.

I'm going to test the stick coils and check the plugs tomorrow. I'll try to get a video of the bike idling and show you an example of the bog at 4k when revving.

Also, how badly would an improperly sealed gas cap affect mpg, if at all?
 

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A valve clearance check is definitely on my list of to-dos.

I'm going to test the stick coils and check the plugs tomorrow. I'll try to get a video of the bike idling and show you an example of the bog at 4k when revving.

Also, how badly would an improperly sealed gas cap affect mpg, if at all?
Is there no chance you can get your money back on this bike? Is there a lemon law in NV?
 

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Is this your first bike?

Stupid question, but are you sure you're filling the gas tank completely? Are you refueling after the gas light turns on?
 

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Discussion Starter #12
It's an 03, no turning back lol

And yes it's my first bike, pain in the ass so far. But I love it for some reason. After I check the coils, I'm going to ride it more to see if my 85 miles in two tanks is accurate.

The speedo is off, so I assume the trip is off as well. I'll do more calculations after I get more data.

I think I'm filling it up all the way. I've been using cash and putting in about 3-3.2 gallons after the light turns on. I'll use a card to make sure fill it up all the way next time and give you guys an update.

When people say they get 120~ miles a tank, do they mean until NEAR empty, or when the fuel light turns on?
 

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My light turns on usually at 130 miles. I'll fill up at around 150 miles and fill back up with 3.5 gallons.
 

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When people say they get 120~ miles a tank, do they mean until NEAR empty, or when the fuel light turns on?
Depends on the person, just try to fill it to the same visible level on the tank each time and check the fuel pump for how much you put in. If need be use google maps to determine how far you've actually ridden. The gas pump fuel gauges aren't always perfect, but they are calibrated at least yearly so they're usually pretty accurate.

As I recall I'd get about 40 to 50mpg on my 2004, so you shouldn't be far off if the bike is running properly.
 

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Discussion Starter #15
I've seen people post screenshots of apps that tell them where they traveled and how many miles they did. Do you guys know of any apps that do that? I'm trying to look for a free one but I cant find one.
 

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Discussion Starter #18
Yeah I'm getting only about 75-80 miles until my fuel light turns on. The bike spews black smoke only when its in the high rev range and it smells like fuel. When it comes back down to idle, it nearly dies and I have to give it some gas so it doesn't. It doesn't smoke when riding normally.

It's not giving me any codes, so would it be the fuel pump or the injectors?

I tried looking in the manual and I couldn't find how to diagnose whether or not an injector is leaking. How do I check for that? Would it be the audible test?
 

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Discussion Starter #19 (Edited)
The bike isn't spitting out any codes.

Here's how it rides. I have shitty gas mileage, idle is a bit choppy, when I'm in first and I'm letting the bike roll, its as if I'm blipping the throttle slightly. It sounds a bit rough when I'm riding steady at 4-5k rpm. Backfiring after I let off the throttle sometimes. And there's black smoke that smells like straight fuel after revving high rpms. Sometimes when I pull in the clutch, the bike will start to dip below 1k and will start to die if I don't give it throttle.


Also I recently replaced the plugs after the bike wouldn't start because they were fouled, now they're black again, all of them. So all of the cylinders are getting spark.

I'm thinking it amy be the fuel pump. Any ideas?
 

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I'm not sure if it matters with these bikes ( not sure how the fuel system is set up?) but I had a fuel injected truck that the fuel pressure regulator messed up on. It would start up and run like crap, turned out that it was locked with the injectors putting as much fuel in the cylinder as it could. It was actually washing past the rings and was entering into the oil. Mechanic said it had a extra quart of oil/gas in the pan and was a ticking bomb. Not sure if this is even possible on these bikes but might want to keep an eye on it if you are still riding.
 
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