83 KZ440 won't rev, loses power, runs away

Hello all,

Warning - long post!

I have an odd problem with my bike - it's a 1983/4 kz440ltd. When I bought it it was only running on 1 cylinder - jammed float.
Anyway, I've taken both carbs off, rebuilt them with new jets and components and she now starts up and runs on BOTH cylinders!
I've also put on new spark plugs, caps, HT leads, battery and the bike has a full tank of new fuel. Standard airbox. The following problem may or may not be two unconnected ones - just to keep you on your toes! (and me)

The problem - up to 6.5ish RPM, it pops and bangs a little but it's generally alright, pulls well as you'd expect it to up to 6.5k then suddenly it loses ALL power under load. I don't mean it's no good above 6.5 k, I mean it's lost everything all through the rev range that it had a second ago. It'll rev freely with the clutch in, but you have to rev it and slip the clutch like hell to get it limping along at walking pace. If you pull over for a minute or two and let it tick over it'll be fine again up to 6.5k. I'm sure it's not just dropping a cylinder, I've ridden it back home on 1 cyl and my girlfriend's 125 so I know what that bike feels like as a 220cc single. It's a gutless but functional vehicle - this is far worse.
If you suddenly snap the throttle open it'll accelerate as it should (up to 6.5 of course). I thought it might be sudden throttle movements but clearly not. I tried going slowly up to 6,5 and I had an almighty bang when it got there and the engine started trying to rev itself to pieces (that's twice that's happened now, but the first time was under different circumstances, that was when I was limping home as above). Though all the other times I got it to 6.5k it's just died like above.

I've lubricated the advance mechanism and it moves pretty freely now (not perfect, but pretty smooth). Carbs have been rebuilt, though I noticed the diaphragm had a repair (maybe both?). Oh, I also changed one carb boot - couldn't get the other one off. My next port of call will be new diaphragms, which might solve the popping and banging, but I can't imagine they're responsible for everything?
Oh, in case the fuel tap facuum wasn't letting fuel through I ran it on Prime as well and had the same problem.

Losing ALL power when you hit a certain revs is something I've never come across before. It's so predictable I can do it at will.

Sorry for the rambling post and thankyou in advance for any advice.

Dan

Check to ensure your fuel line does not have a kink or any sharp bends in it. Ed

Bad diaphragm will indeed cause running issues especially at higher RPM. Now you can probably change the diaphragms with the carbs still mounted to the engine but If it were mine I'll pull the carbs again and go through them. Make sure the last thing you do is to set the fuel level with a clear plastic tube as per the FSM.

Hello,
Thanks for your replies, they are appreciated. I'll get the diaphragms on as soon as I'm fixed. At the end of the aforementioned test ride she threw me off while I was trying to keep the runaway revs down with the brake and lost the front end in the wet. So I'm a little sour at the minute! I'll post back how I get on.

Use penetrating oil and impact driver to get that other boot loose and replace it. The 440s are notorious for leaky boots.

I had issues in those rev ranges with my 440 and it was a combination of leaky boots and a locked up advancer.

I completely tore down the advancer, polished it up, lubed then reassembled and haven't had any problems since.

I hope you were not seriously injured. That is a pretty sucky way to ring in the new year.

dom2570 wrote: Use penetrating oil and impact driver to get that other boot loose and replace it. The 440s are notorious for leaky boots.

I had issues in those rev ranges with my 440 and it was a combination of leaky boots and a locked up advancer.

I completely tore down the advancer, polished it up, lubed then reassembled and haven't had any problems since.

Usually you can get one screw out and the other is stuck. Remove the screw you can get out and hit the boot in a counter clockwise direction. Most of the time the screw is stuck to the boot and spinning the boot will loosen the screw.

Hope you get well soon and you weren't too injured. That just sucks!

If new diaphragms and cleaning the advance mech doesn't fix it, I'm going to have to get the carbs off again. I've replaced the right boot but couldn't get the left one off. I was hoping that if I was too stuck to move it was too stuck to leak. More fool me!

Thanks for the concern - nothing broken on me, arm's not quite got all the movement back yet and I can only wear toecap boots because my toenail's gone black and hurts squeezing it into normal shoes. But I'm generally OK now. Word to the wise - I was only going up and down the road on the test run so considered not bothering pulling on my full bike gear. Luckily I did so - I'm not sure how I'd have fared in ankle boots and jeans!

crofty1984 wrote: If new diaphragms and cleaning the advance mech doesn't fix it, I'm going to have to get the carbs off again. I've replaced the right boot but couldn't get the left one off. I was hoping that if I was too stuck to move it was too stuck to leak. More fool me!

Thanks for the concern - nothing broken on me, arm's not quite got all the movement back yet and I can only wear toecap boots because my toenail's gone black and hurts squeezing it into normal shoes. But I'm generally OK now. Word to the wise - I was only going up and down the road on the test run so considered not bothering pulling on my full bike gear. Luckily I did so - I'm not sure how I'd have fared in ankle boots and jeans!

Glad you are okay, I've been thrown off both my 440s screwing around in the dirt. Gear or no gear, it is never fun.

The boots on these bikes are strange, mine appeared to be fine, but once I got them off I discovered big cracks. The JIS screws that hold them on are certainly a pain in the ass to get off.

If the screws are stuck, soak them in Kroil or a 50/50 mixture of acetone and ATF for a few days, applying a little more once or twice a day. A good JIS bit in a hand impact driver is pretty handy, too. If you cannot locate a JIS bit, you can modify a Phillips bit to fit the JIS screw heads. Do a search here for a post by 650Ed on how to make the modification.

Here is a source for JIS screwdrivers
www.gofastinnovations.com/


Here is a thread with more links
www.kzrider.com/forum/21-tools/598060-ji...drivers?limitstart=0

TexasKZ wrote: Here is a source for JIS screwdrivers
www.gofastinnovations.com/


Here is a thread with more links
www.kzrider.com/forum/21-tools/598060-ji...drivers?limitstart=0

I think the guy who owns gofast is a forum member. I've checked around and he by far has the best price on JIS screwdrivers.