Surging at between 4-5k RPMs - 2003 VFR800

I am a relatively new owner of a 2003 VFR800. I noticed that in 3rd gear between 4-5k rpm's, particularly between say 4500 and 5000 rpm's, the bike seems to surge a bit. I don't hear any change in the exhaust sound, which is the most overpowering sound at the time as my exhaust is gutted. Its almost as if its losing power for like a spilt second, and then its back, and then its gone again, and its a random pattern. It happens in other gears too, but seems to be more noticable to me in gears 1-3.

I have never checked the plugs, and I am concerned perhaps it runs rich as I have the gutted exhaust. Would fouled plugs cause something like this?
I have no Power Commander, its on my list of things to get (with a dyno tune), perhaps this is the likely culprit?

The last thing I am very concerned about. I noticed my rear rotor is "very" rough. I mean I can really feel the ripples in it.....thing is toast. I was told when it was at the dealership that the rear pads had only about 25% left, but they never mentioned anything about the rotor, but in all honestly I think they didn't look over the bike very well (it was a general "check out" after purchase of this bike used). I don't use my rear brake much, but after pulling in tonight, I noticed the rotor is HOT. This combined with its ridges on the rotor has led me to believe something is going on back there. I do hear it rub when I turn the wheel, I thought this is normal.....
The reason I bring this up, is perhaps its my rear brake dragging causing this surging? Not sure why it would be more pronounced at lower speeds (gears 1-3), but I don't spend a lot of time below 4k RPM's in those gears, so that may be why I "notice" it more between 4-5k RPM's. I was going to tackle replacing the rear brakes and rotor, but now that I notice its hot, which probably led to the demise of my rotor in the first place, perhaps the caliper needs to be re-built and I have never done that before so I will probably just take it to a shop and have them do a total check-out on the brakes and put the new pads/rotor on. I don't want to install the new parts and then have them get hosed from some issue with the caliper going on.

Anyways, any other usual suspect things I should check out as far as this surging? It's not drastic like yank your neck or anything like that, its a very subtle but you can tell its happening.

 

Hard to know, but the surge at that RPM is fairly common with the stock EFI. It is cured with a PC and Dynotune, along with the other mods that address fueling.

The rear rotor may be a separate issue.

 

1. Minimum thickness is stamped on the rotor. The roughness can be machined off the rotor if you don't go below the minimum thickness. Check this with a dial caliper or micrometer.
2. Check the operation of the brake caliper. This may need cleaning. Remove the brake pads and make sure the pistons move freely. They may have to be removed and cleaned. After all is done you will probably have to bleed the brakes.

 

Prob won't help your surging issue, but one thing you might add onto your to do list is to block the pair valve. I have an 03 as well and it really helped throttle response even out. Bike became immediately more rideable.

Also- I think an open exhaust would create a lean condition- not rich?

 

A worn out chain can do it as well. Check for tight links.

 

Regarding the rotor, are there really places that will turn a motorcycle rotor? I figured those didn't get turned. In any case, the ripples on it are pretty bad. I have already ordered a new stock rotor, so perhaps if I can turn this old one I leave it as a spare. Also if I remove the brake pads, pull the caliper out, and clean it real good, say with a brush, and compress the pistons , work them back and forth a bit, and finally put the brakes back in, why would that require bleeding the system, shouldn't the system stay sealed at that point assuming I don't push a piston all the way out?

 

I have the pair blocks on order (I am going to rip all that pair stuff out and just put in the block plates nice and clean). I am not sure if gutted exhaust creates more of a lean or rich condition, for some reason I thought it created more of a rich condition. I can't wait to put a PC in with a dyno tune.......have been quickly sinking money into this bike, I wont be happy until it purrs.

 

to do that would I remove the chain? I have never removed the chain, I will google on how to do that. I did measure the slack, and it was a "bit" over recommended, it is suppose to be like between 1" - 1 3/8" and I think mine was at about 1 1/2". Perhaps I should tighten things down closer to 1"

 

No need to remove the chain! Put the bike on the center stand, put the transmission in neutral, and check the chain play like your owner's manual describes. You can check the entire length of the chain for uneven wear (tight sections and loose sections) by turning the rear wheel to expose different sections of chain. Keep checking until you have checked the entire length of the chain. Alternating tight and loose sections could be causing a surging sensation at constant RPM. It means your chain is shot and you need to replace it, along with a new countershaft sprocket and rear sprocket.

Hope that makes sense?

 

Oh, and if your chain is shot, make sure you don't over tighten it while you wait for your replacement chain kit. If that is the situation, check back in here on how to adjust a shot chain . . .

 

Sorry about the late reply. I don't know of anybody in my area that actually does machine motorcycle rotors but any machine shop has the capability. It would involve talking them into doing it. You could try a brake shop and see what they say. The hardest part is to find a way to properly hold the rotor.

As far as bleeding if you remove the pistons you will have to bleed.