Gpz900 stutter at 6k and lack of high end power

 greetings everyone I have Been bringing my 1985 GPZ 900 back to life. I posted before because I was having trouble with the carburetors and I bought a jet kit and installed it and it is running a lot better! I have no low RPM stutter and they bike idles perfect and has more power now. However I have perfect acceleration till about 6000 RPMs and then it stutters and then I have a lack of power till Redline it will accelerate the red line but I can tell it's not at full power.  Should I go up another jet size? I have 145 main, 42 pilots, and clip on the needle is 4th from top, which is 1 richer then stock. 2.5 turns out on the carbs. Bike has after market exhaust and air pods. I have 155 main jets I can try, or should I adjust the needle clip 1 more richer ? Maybe go to 3 turns out on the carbs?  Thanks in advance. 

Have you following my advice.

kzrider.com/kunena/2-engine/608956-troub...h-gpz900-rpms#787815

A valve check/adjustment is necessary if you try to optimized your carb setting.
If not it´s a waste of time to go into a carburetor/jet fine tuning.
Do you a favor and do the mechanically basics first...

Hey thank you for your input again and sorry for the late response. I have been on vacation. I did do the valve adjustment a few of the valves were slightly off but after the adjustment the result is still the same. I even pulled the valve cover a second time and verified all the clearances were correct. I don't know if this matters but when I pulled the carburetors off today after a test ride to try a different Main Jet size there was a little bit of extra Fuel and fuel Vapors coming out of every cylinder and a little bit of smoke. I'm not sure what else to try. Now the bike Only pulls till about 5000 RPMs and it runs absolutely perfect till then. But above that it struggles it will go to redline but it's sputters the whole time. My instinct tells me main jet, but it's already got a 140,and the jet kit i bought came with 145s and 155s. I upped the pilot jets to 37.5s. I'm out of ideas and kinda getting tired of this old bike, unfortunately.

Have you checked the float level in the carbs? I had same symtoms, problem for me was the float needle and incorrect height.

Are your carbs running on pot filter or stock air box???

I'd be curious to see the result of a plug chop test. Google search the term and then implement it if possible. It would suck to hole a piston before you find the trouble.

I'm assuming you left the baffle in the pipe, if not put it back in or get one. Also, if the pods haven't been oiled then oil them unless the manufacturer explicitly says not to. Oil restricts the flow of air... Not a lot but it might be a simple quick test or at least a clue as to what is it isn't happening.

Thank you everyone for your responses. The bike has pod filters. It ran great last year with the Pod filters. I did not oil the air filters so I do not know if they have oil. I will try some oil and see if that helps. I did leave the baffle in the exhaust pipe. But like I said before this bike ran 90% last year without changing any parts. I will Google the plug chop test and see what I can find. The system does not seem lean because the spark plugs are a little on the dark side on the electrode. I have not checked float level in the carbs I will research this and get back to you . Thanks again

This post intrigues me on a few levels. The assumption that some bigger jets and/or a needle setting will be the panacea for an ill running motor is wrong headed. I'm not saying it's impossible to achieve but let's take a closer look at what is reality in this particular situation.

The motorcycle manufacturer together with the manufacturer of the fuel delivery system produce an engine that performs well under a certain set of conditions that are well rounded for daily riding. Some owners want to alter this for whatever reason and that's fine but not without considerations. Installing aftermarket pipes and freer flowing intake filters changes what the manufacturer intended and to find the new well rounded sweet spot might actually not be achievable anymore.

With carburetor the fuel is sucked up by engine vacuum with what is called the venturi effect. But if the engine vacuum now pulls more air in than fuel (simply because it's easier) then you have a lean condition instead of an optimum fuel to air ratio. Installing a bigger jet and allowing more fuel to come up may not be an adequate solution because the correct atomization might not occur so the fuel droplets that are mixed with air might not burn fully.

It's one thing to get more air and fuel for a racing application but for the street you take the risk of not being pleased. Of course if you have a pit crew and engine builder in your employ then that's different.

I'm not saying not to install them, and finally arriving at the elusive sweet spot after much trial and error can be a challenge and a rewarding experience. But if you would rather have everything go smooth without so many problems then you might want to stick with the stock set up.

They are on the dark side because you took them out after the bike was shut off at likely an idle. The plug chop will reveal what's happening at higher revs. This will be a fun one to figure out.

Also, as Scirocco mentioned and we've discussed before, knowing basic engine health, ie; compression ratio and valve clearances is really helpful if not essential to a good diagnosis.

Thank you for your response. I'm sorry I did not make it clear in my first post but I bought the bike this way from a friend. I rode this bike a little over a year ago and it ran really great with just a tiny stutter around 2,000 rpms. However it pulled really hard the whole way to Red Line in every gear. With the pods and exhaust. The reason I bought the jet kit is because I was thinking maybe when the mechanic rebuild the carburetors he replaced the Jets and maybe used stock Jets. My friend barely rode it in the last year because he has a different bike. He would start this one weekly let it warm up and ride it around the block. He didn't like the low RPM stutter so he took the carbs to be rebuilt and after bringing them back and installing them the bike runs like this. I acquired this bike 3 weeks ago.