TOPIC:

Picked up an '82 KZ440-G1 back in February as my first bike. Been running great, only replaced a tire and changed the oil on it, and has ~22,000 miles on it. I've noticed though that it really struggles on the freeway, barely holding 60 in 6th gear at WOT, and 65-70 in 5th with near WOT buzzing at ~6200RPM. I get that it isn't the biggest of bikes, but, I found it hit it's top speed of maybe 73-74MPH at redline in 4th with WOT, and, for a bike that was rated at going over 100MPH according to the manual, there must be something wrong with it to be unable to maintain freeway speeds gracefully.

I've not done any real work to this bike since I've bought it since its always started up without issue and seems to have decent power getting around town. I have no real basis on what to compare this bike against, so, I don't know what speed and acceleration is normal. Engine sounds healthy along with the transmission, so, no worries there that I can tell.

Any suggestions on what to check on this bike? I can't find a service manual for this year with the electronic ignition, so, I'm not really sure what to check beyond setting the valves and checking the plugs. It does have the typical torn carb boots for a KZ400/440, but, I can't feel any air being drawn in, so, I've discounted that so far.

Replace your carb boots. If they are cracked and not leaking they soon will be.
What condition is your air filter in? Pics?


.

Check the spark advance and lube it if needed.
Steve

dakiato wrote: Picked up an '82 KZ440-G1 back in February as my first bike. Been running great, only replaced a tire and changed the oil on it, and has ~22,000 miles on it. I've noticed though that it really struggles on the freeway, barely holding 60 in 6th gear at WOT, and 65-70 in 5th with near WOT buzzing at ~6200RPM. I get that it isn't the biggest of bikes, but, I found it hit it's top speed of maybe 73-74MPH at redline in 4th with WOT, and, for a bike that was rated at going over 100MPH according to the manual, there must be something wrong with it to be unable to maintain freeway speeds gracefully.

I've not done any real work to this bike since I've bought it since its always started up without issue and seems to have decent power getting around town. I have no real basis on what to compare this bike against, so, I don't know what speed and acceleration is normal. Engine sounds healthy along with the transmission, so, no worries there that I can tell.

Any suggestions on what to check on this bike? I can't find a service manual for this year with the electronic ignition, so, I'm not really sure what to check beyond setting the valves and checking the plugs. It does have the typical torn carb boots for a KZ400/440, but, I can't feel any air being drawn in, so, I've discounted that so far.

Admittedly, I am a little guy at around 5'6" and 140lbs dripping wet but, I had no trouble getting my KZ400 up to 80-85mph in top gear when in good tune.

Have you checked the valve clearances?

I am 6' 3" and 220lb and could easily maintain freeway speeds on th kz400 I used to have.

I had similar on my new '84 440. Turned out it was only running on the right cylinder!
Easy test - start it and then pull a plug cap off. If the engine starts to struggle or dies then you know that cylinder's at least doing something. No effect and you know that that particular cylinder wasn't contributing much to the party.

I don't know if this will help?

My build blog

I hope that's allowed.

Dan

Many thanks for the assistance everyone, much appreciated.

New boots came in and I installed them today - Made a huge difference on choke and idle, no longer races up and down and warms up in a reasonable-ish time now. 6th gear now just about holds 67-70MPH with WOT, and the bikes top speed remains at 75-78 at 8000RPM with WOT, which lead me to think there's something else worn on this bike too. Checked all 4 valves whilst I had the tank off, and, all seemed within spec with my feeler gauge.

I inspected the timing mechanism and it's advancing and retarding with the throttle without issue, and the weights extend all the way out at 3k+ RPM, so, I think that part is good. Greased it up as well just in case, but, noticed no difference in power. Also regarding the air filter - When I bought the bike I found the original air filter element had gone rock hard and crumbly, so, I replaced it with a lightweight foam. Tried running the bike without it and noticed no real difference.

So, I ran a compression test on it after a good run on the freeway (Probably 30 minutes after I turned it off), and, saw quite depressing results. Cylinder 1/Left is reading ~65 psi, and 2/Right is reading ~80 psi. Unless I'm measuring this wrong and there's some special procedure needed, this bike is reading remarkably low. It's not blowing any smoke or burning any oil that I can see, so, I'm quite confused on why the compression is so low on this bike at only ~22,000 miles. Certainly explains the lack of power however.

Quote != edit

dakiato wrote:
So, I ran a compression test on it after a good run on the freeway (Probably 30 minutes after I turned it off), and, saw quite depressing results. Cylinder 1/Left is reading ~65 psi, and 2/Right is reading ~80 psi. Unless I'm measuring this wrong and there's some special procedure needed, this bike is reading remarkably low. It's not blowing any smoke or burning any oi that I can see, so, I'm quite confused on why the compression is so low on this bike at only ~22,000 miles. Certainly explains the lack of power however.

When you did the compression test did you have the throttle at wide open or the carbs off the bike. WOT makes a big difference.
Doubt the bike would run with 65 and 80 psi

JR wrote: When you did the compression test did you have the throttle at wide open or the carbs off the bike. WOT makes a big difference.
Doubt the bike would run with 65 and 80 psi

Ah, you are correct, never done a compression test on a bike before. Ran it with the throttle all the way open and they both read 150psi exactly. I suppose the only thing left now to check is the carb itself - Perhaps the jets or seals have gone after all these years.

Click on the "Articles" tab above and check out Carb Cleaning 101 and 102 for some usefull tips.

Also www.kz400.com/index.html will have some usefull stuff with photos

Good luck

You put in a foam filter. Check your plugs. Might be too lean. Pics.
Steve