1995 ZX-6R F1 flutter on hard acceleration

[knucklebuster01]

Hello all, my first post here so a big hello and thanks in advance for helping out.

1995 ZX-6R F1 series with 34k on it. I just bought it used a couple of months ago and, though I doubt it's been loved like it should've, I don't think it's in bad shape. No smoke, clutch seems pretty tight, ect. Needs some upper gaskets but nothing too major.

Work I've done so far;
oil change & filter
plugs
air filter
petcock rebuild & fuel lines replaced
seats re-covered and driver's seat xtra foam added

The bike runs really nice at idle and low speeds, and at acceleration to about 5-6k you would never really know there was a problem. However, if I get down on it and blast it up to 10+k it really gets fluttery (best word I can think of to describe it) between 6.5 - 9k rpms. I've been told this could be due to the machine running thin(that's what it feels like to me). I have plans to get the carbs tuned at the shop(never done tuned multi-carb machine), but I just want to do all I can first so that I know the carb tune needs to be done and will help. It was leaking fuel like a civ before and that's why I rebuilt the petcock and replaced the fuel lines(which actually helped performance at least a little). I'm also curious if it could be the valves as I noticed a disgusting amount of build-up on the top of them when looking down through the carbs. I also read lots of posts before posting this question which suggested valve adjustment should be needed at the current milage. I can run the bike over 100mph easy. It's not backfiring or stalling really, it just gets a weird miss with hard acceleration at the specific range or 6.5-9k rpms. I've been riding since I was 14 and I'm 32 now. I've owned many bikes and worked on them all myself. I'm also a decent auto mechanic so I know I can do what needs to be done, I just can't identify the exact problem on this deal. Any suggestions will be greatly appreciated.

[MagicNinja]

Well there's no question you should have your valves checked. Who knows if Mr. Previous Owner had them check. But its probably not your problem. The valves are in the head of the engine. What you're talking about seeing through the carbs are the pistons. They are probably covered with lots of carbon.

Fluttery feeling ususally means its running lean. A wet or bogging feeling means too rich. Try cleaning your plugs and then then re-installing them and running the bike only where it feels fluttery for a while. Then pull the plugs. The color will help determine whether its rich or lean.

Its probably lean, and since its running bad between 6 and 9 grand your mid range will probably need adjustment. You can shim out your needles with washer to give it more gas at midrange, or if you have a jet kit you can move the clip down the needle.

Also check your float levels. These limit how much gas gets in the carb bowls, if they are set too low the bowls will not fill and you could starve the bike for fuel. Though the setting may be ok if you can run good at wide open throttle.

You said you rebuild the petcock. Make sure you are getting adequate fuel from the tank to the carbs it may be just that simple. I always have a see-through fuel filter inline on the gas hose after the petcock so I can monitor the fuel at all times.

[knucklebuster01]

Thanks MagicNinja. I did check the fuel flow from the lines post petcock, and the fuel was flowing freely in both on and reserve positions. The plugs are brand new, but the old ones were on the light side, kind of greyish brown for lack of a better description. I still have them and will post a pic later. There was a lot of leakage in the fuel lines and petcock so I'm afraid they will give some false info. As for the valves, I'm 100% sure where, and what the valves are and look like, and I was looking through the top of the carb down onto the intake valves which reside directly below the induction ports. I could see through to the piston heads as well, and they weren't as built up with gunk as the back side of the valves, from seat to stem. I have a see thru filter in the line as well, it's just almost impossible to see without removing the tank. My bike is a F1 series and, as I'm sure you know, there are many variations of these bikes and thier setups. I think I'll just have the shop tune the carbs for me and let them tell me if the valves need to be adjusted, which I'm 99.9% sure will need to be done. I just can't afford to have the bike down at this time. I need to re-seal the forks and they want a pretty nice chunk to do it. I've been reading on it here, but just not sure I want to risk doing it wrong.

[MagicNinja]

I missed where you said F1 series. I can't see my valves through the carbs, unless maybe I took them off and used a telescopic mirror or something. If you have the money take it to a shop. The carbs are difficult to tune and get them "just right" but easy to work on. Forks are a PITA but can be done if you're a decent mechanic. As long as you make note on how you took them apart, you can get them back together. My 250 had a bad leak, the only issue I had was compressing the springs to get the bottom bolt in, and I had to rent a seal driver. You should be able to pull it off and save some cash.