High end troubles

My 78 KZ650 runs pretty good at low end, but the high end leaves a lot to be desired. I can get up to around 60 MPH in 3rd gear toward the higher end of the RPM range, but 4th and 5th gears only get me about 10 more MPH as the bike starts to surge and bog all while the RPMs still go higher. When I let off of the gas down to about 5k it will pick back up a little but around 6500 RPM the bike just loses all power even though the it is still revving at a higher and higher rate. I am thinking this is a jetting issue and it is only starting to come up because I don't go on the freeway very often and rarely get above 60 MPH. Any thoughts?

I have Pods and do not own an airbox. Currently my mains are at 118, but the same thing happened when I had 110s in. The difference for the jump was because I got the 118 with a stage 3 jet kit. Also when I had the 110s in the mid range RPM (4k - 7k) got very high pitched.

I always end up suggesting a complete tune up , but what do the plugs look like ?
Dave

Dave here are the plugs. I did the timing about a week ago so that is pretty good. The plugs look a lot like I'm running rich. I think I may need to grab some sub 110 mains if that is the case and go from there.

You might want to lower the needle valves a notch too. Put new plugs in so you can read them
Dave

Unfortunately I cannot lower the needles, they are on the first notch. I thought I would start there and see how it went. So, I am going to have to lower the mains altogether. I bought some 107.5s and I still have the original 102, but if I recall correctly the 102s were very lean on the top end, but then again I could be completely incorrect about that.

118 mains where did you get them because they aren't Mikuni jets.

I'd start with 17.5 pilots 117.5 mains needle one notch up from the bottom
looking at the needle as it's in the carb.meening point down.

Looks like oil to me. Making it richer just made it worse. New plugs and look for oil. Go back to stock set up and start again.
Dave is right. You want Mikuni jets. The others are drilled differently. I put in new 125's and pulled out the Miks I thought were 127.5's. They were Mik 125's the others were another brand. Instantly I had a huge flat spot. Wouldn't run for ST. I compared the two and they were different, way different. I put my old jets back in and are running them today.
Steve

For the life of me I can not see any reason in a non race bike.... where you would have to move the needle position more then one groove up or down from the stock slot.
However, be careful here because amateurish recommendations or novice carb and ignition tuning can get you into this kind of dilemma....
Sometimes a tweaker has to back up the boat and start from the stock settings again and this time, a little at a time...

From my friends at the KZ650 info page:
forums.kz650.info/index.php?topic=1853.0

]When my 900 did that it was a restricted fuel filter. There is also one on the inside of the tank on the fuel valve

zukdave wrote: 118 mains where did you get them because they aren't Mikuni jets.

I'd start with 17.5 pilots 117.5 mains needle one notch up from the bottom
looking at the needle as it's in the carb.meening point down.

This is where I was with the stock motor and pods/Header and with my new set up..... was running very good although a hair rich stock and about perfect with the 700 kit ...... the 118 mains that come with the carb kit I "think" I read somewhere are equal to 110 stock jets and the nettle is different too....... hopefully someone will chime in on this.

You should leave the needle in the middle position. That is meant for minor elevation changes and fine tuning the mid range. I mentioned oil because when I was burning oil due to bad valve guide seals, I had to go with smaller pilots. I basically had a 2 stroke so to speak. When I did my valves, it was too lean so I went larger jets. Something to think about.
Steve

swest wrote: You should leave the needle in the middle position. That is meant for minor elevation changes and fine tuning the mid range. I mentioned oil because when I was burning oil due to bad valve guide seals, I had to go with smaller pilots. I basically had a 2 stroke so to speak. When I did my valves, it was too lean so I went larger jets. Something to think about.
Steve

In a 2 stroke, too much oil makes the mixture run too lean, not the other way around. I wonder if in a 4 stroke mixing oil in like that would simulate too lean too. ?