KZ440 slowly tops out to only 60

Hello! I was recently given a 1981 KZ440 LTD A2 that had been sitting for 5 years and was not in running condition. It had 11,500 miles on it and is in good shape besides being a little dirty. I put in quite a bit of work to get it running and my first time out I could get it up to 85 fairly easily. Now 2,500 miles later it tops out at only 60-65 and it take a while to get there. It idles perfectly once its warmed up. It will go to redline in the first 3 gears, but in the last 3 it won't make it all the way there and by the time I get to 6th it can only make it to about 5,500. Here is a list of what I did when I first got it:
Checked compression, it is at 125psi after 3 cranks and will get up to 150psi by 6 cranks.
adjusted value clearance
changed spark plugs
cleaned carbs very well and used a rebuild kit while doing so
replaced the carb diaphragms
put on new carb boots
cleaned the air filter
changed oil and filter
put in a relay to raise the voltage to the coil
replaced the chain (At 12,500 miles)
new tires
rebuilt the forks
replaced the clutch cable
lubricated all the points outlined in the service manual including the timing advancer
lubed the chain every 300 miles

I started to notice the drop in the acceleration and top end at around 12,000 miles and it seemed to get worse after replacing the chain. I'm now at 14,000 miles and I just changed the oil and filter again and cleaned it up a little. I checked the compression again and it has not changed. I did notice my oil level seemed to be slowly dropping since my last oil change and there are no leaks. I'm confused as to where it is going because I don't see any blue smoke coming from the pipes even at high revs. In the air box there does seem to be an oily residue and I figured that was from the crankcase emission control system. From the service manual, "The system eliminates the release of crankcase vapors into the atmosphere. Instead, the vapors are routed through and oil separator to the intake side of the engine." Could there be something wrong with the oil separator and could this cause any performance issues? I also have some exhaust leaks around the baffles due to rust, but that has not changed since it was able to hit 85.

Any help anyone can give would be fantastic because I'm starting to get pretty frustrated. Thanks!!

I may be off-base, but my first thought turns toward the fuel system. When getting the bike back on the road did you put an inline filter between the petcock and carbs? If so, maybe it is dirty and it should be changed / cleaned. If not, maybe some crud from inside the tank has gotten into your carbs in which case they may need to be cleaned again and an inline filter installed. Also, have you checked the screen on the petcock? It is possible that it has become partially clogged from crud in the tank. Ed

I replaced the fuel lines, but I did not put in a filter. I also cleaned the tank with a degreaser and a short piece of chain to knock lose anything. I then removed any rust using electrolysis. When I was done Rinsed the tank with fuel before even putting it back on the bike. That being said I have not checked the screen since then and I have not pulled off the carb bowls in quite some time, so I could see the possibility of a clog there. If fuel isn't getting to the carbs fast enough should I notice a sputtering when it tops out or even in the lower gears? It seems to still run consistently when I get it up to 60 and it doesn't seem to make a difference between 3/4 throttle and full. I'll pull off the carbs and petcock and check for any clogs just in case.

Valve clearances checked? If not way overdue. I'd start there.

I checked the valve clearances when I first got it. Is it possible they got vary far off in 2,500 miles? is that something I should be checking every oil change or more often?

Lubing the timing advancer was a good idea.

If not already done, would use a timing light to view and confirm that the timing advancer is functioning properly by quickly moving back and forth as rpm is varied by blipping the throttle.

Good Fortune!

I worked on one of these bikes once that would not get up to speed and finally found that a magnet had come loose in the stator.

Try other suggestions first before removing the cover.

I pulled off the carbs today to take a look in the bowls and the fuel lines for any clogs. It all looked fine till I tested the diaphragms and they snapped shut with no seal at all. I'm glad I can pretty confidently say this is whats causing all my issues, but its weird that my brand new diaphragms would only last 2,500 miles. The last two pictures are two different tears in the same diaphragm.

Thanks for all the help and suggestions!

KonfusedKZ wrote: I pulled off the carbs today to take a look in the bowls and the fuel lines for any clogs. It all looked fine till I tested the diaphragms and they snapped shut with no seal at all. I'm glad I can pretty confidently say this is whats causing all my issues, but its weird that my brand new diaphragms would only last 2,500 miles. The last two pictures are two different tears in the same diaphragm.

Thanks for all the help and suggestions!

Yuk! :sick:
Will the company you bought those from warranty those, maybe have a better quality set for you? The OEM ones lasted for So many years, and those new ones, well are Junk.

KonfusedKZ wrote: I pulled off the carbs today to take a look in the bowls and the fuel lines for any clogs. It all looked fine till I tested the diaphragms and they snapped shut with no seal at all. I'm glad I can pretty confidently say this is whats causing all my issues, but its weird that my brand new diaphragms would only last 2,500 miles. The last two pictures are two different tears in the same diaphragm.

Thanks for all the help and suggestions!

The Keihin cv34s on the KZ750/4 ( h/LTD and e/standard ) use the same slides.
Find yourself a rack of four and have 2 spares.
I have no idea if the cv38s off the KZ750b ( twin ) or the cv32s off the later KZ650 will swap or not.


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