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Hello all,
A couple weeks ago I picked up a 77 KZ400. It ran fine when my buddy and I went to look at it. He drove it 80 miles back to our place with no major problems. We did notice however a stutter almost like a rev limiter around the 4500-5000 rpm mark. Took the carbs apart and cleaned them. They looked very clean inside to start with. After putting them back on it idled fine but stuttered when throttle was opened and held making it unrideable. It revs fine if you turn the throttle quickly. We reset the idle based on the instructions in the owners manual but still had the same problem. We then realized that there was a small tear in both of the vacuum diaphragms which we did not notice previously. I bought two new slides with diaphragms from Kawasaki. I put them in today to replace the ripped ones and the issue still remains. The bike does have some dumb straight pipe mufflers on it and I do believe the jetting is stock. Does anyone have any ideas what I should try next? I am kind of at a loss. Thanks!

Get some mufflers. Does it have the stock aribox and filter? Removing the mufflers or removing the airbox and installing individual filters will cause the engine to run quite lean. I hope it did not get too hot on the trip home.

I just re-read your post. What do you mean by straight pipe mufflers? The term straight pipe refers to pipes with no mufflers.

Thanks for the quick reply. It does have the stock air box and filter. Hopefully it didn't get too hot on the way back... I have blown up an engine before due to detonation (long story lol). I have seen people say they put steel wool in the pipes. Would this work for the time being until i could get some mufflers? I am not sure where the best place would be to get some stock ones or at least some that would fit properly on the bike.

I suppose steel wool would work temporarily. The real challenge will be to get the right amount in each pipe and the find a way to hold it in place. Finding decent stock mufflers may be a challenge. If the pipes were cut really short, you may be looking at buying a full system. One of the other 400/440 owners around here may be able to help you out. You can also troll fleabay.

By the way, most of the members here are pic-aholics. You may want to post some pics new before they come along and taunt you.

In the mean time, you should check the timing advancer to be sure it is moving as it should. Crud and rust can lock them up, preventing the timing from advancing in the mid and upper rpms. Also check the plugs and plug wires.

Also in the mean time, you really need to get hold of a copy of the genuine Kawasaki service manual for your exact year and model. The aftermarket manuals (Clymer, Haynes, etc) are better than nothing, but not as complete and specific as the real deal.

I have checked eBay for exhausts. I have seen a couple possibilities. I do not believe that my pipes were cut. It looks like it has some sort of slip on pipes. I will have to take look at the timing advancer. The plugs are new. We changed them the day after we cleaned the carbs thinking that may help the problem. The old plugs were black so I am assuming it was running rich. It did smell kind of rich when it did run ok. I have been trying to find a service manual for my bike. I was actually looking at eBay earlier today haha. I don't have too many pics of it yet but here are a couple that I have... The Street Triple R is my roommates.

Nice little bike. Those look like Jardine side drafts. They will work. They have fiberglass packing in them. Youi'll have to jet for them though. Pics of the plugs? Tex covered the things I was about to suggest.
Steve

Thanks! I went down and got a few more pics. Here are some better ones of the exhaust. I never realized it had some sort of packing it it. Thing is pretty damn loud lol. And here is a pic of the plugs that I just put in a week or so ago and this is all from just trying to get it to run right. Looks pretty rich to me.

Problem must lie elsewhere. Valves adjusted?
Steve

No we have not adjusted them yet. We will give that a shot tomorrow thanks.

Those Lu Hao silencers are very inexpensive and may not have any packing, hence their loudness. On the upside, they should be bolt-ons. If so, it will be simple to replace them with something less obnoxious.

The blackness on the plugs could be oil from bad valve seals, but first things first. Check valve lash and insure proper carb adjustments.

With a bike tat old, many problems are possible; I had the exact same bike exclusively serviced my me for 25 years, and here's my thoughts;

1; most likely it's the timing advancer, it gets stuck. The good news is that it's an easy fix.
You'll need a timing light to readjust the timing when you're done anyway; so get one, point it at the timing marks under the right cover, and start the bike. When you rev it up a little, you should see the timing mark move up to the advance marker on the timing plate. If it doesn't, pull the plate off and take out the advancer by removing the center bolt.
Take off the springs and slip the cam off; put a little rubbing compound on the shaft and fit it back together. rotate back and forth by hand for a few minutes, then take it apart and clean it well before greasing lightly and reassembling.

2; the carb diaphragms.
They're 40 years old unless they've been changed; if one has a crack, you've got a real problem on your hands. Maybe someone here knows where to get a replacement.
I changed mine when the bike was just 20 years old.
take off the tank, then unscrew the top plates of the carbs; CAREFULLY peel up the edges of the diaphragms, then pull them out with the slider and jet.
inspect it for through cracks, especially around the edges.

3; not likely, but could be water in the carbs. take out the drain plugs and catch the fuel in a plastic cup to check.

Of course there's a lot more, but that should give you a start.