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77 KZ400 runs rough when throttle opened 15 Aug 2016 04:55 #738718

  • ThatGPzGuy
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I had those same mufflers on my 400 and they were gawd awful. I replaced them with some MAC skip-ons.
Jim
North GA
2016 Yamaha FJR1300ES
1982 GPz750 R1
1974 Kawasaki H1
1976 Kawasaki KZ400
1979 Yamaha XS650 cafe'
2001 KZ1000P
2001 Yamaha YZ426
1981 Honda XR200 stroked in an '89 CR125 chassis
1965 Mustang
1967 Triumph GT6
1976 Bronco
"If you didn't build it, it's not really yours"

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77 KZ400 runs rough when throttle opened 15 Aug 2016 10:56 #738762

  • nodakkz
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Ok so we adjusted the valves this morning then put the carbs back to the stock idle spec per the owners manual. It still has the same issue. It does idle slightly better. I looked at the timing advancer and could see it seem to expand when i rev the engine. I did not take off the points plate yet. The diaphragms were changed yesterday with some brand new ones from kawasaki. Anything else I should try? Is it possible my coil is going bad? Or maybe I need to readjust the points and timing? Or should I skip that and go straight to a compression test? Also I was looking at those mac mufflers or some emgo mufflers. They don't seem too bad for the price.

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77 KZ400 runs rough when throttle opened 15 Aug 2016 11:16 #738765

  • TexasKZ
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Is it possible my coil is going bad? Or maybe I need to readjust the points and timing?

Those seem like reasonable culprits.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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77 KZ400 runs rough when throttle opened 15 Aug 2016 11:58 #738768

  • nodakkz
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I just decided to do a compression test before I keep spending money on parts. The right side came out to 125. The left side was 140. I believe that is just over 10% if I did the math correctly in my head. However, I did not put any oil in the cylinder yet to see if that raised it to check to see if it was the rings. Do you all think this would be enough to cause the problem it is having?

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77 KZ400 runs rough when throttle opened 15 Aug 2016 13:25 #738783

  • TexasKZ
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That is more variance in compression than you would like to see, but that will not cause the problem you are having.Have you checked to see that you are getting good spark? You can remove the plugs, then stick them back in the boots with the threaded part of the plug on the engine so it can ground, away from the spark plug hole. Turn on the key and hit the starter. You should see a fat, blue spark from each plug. If the spark is weak and yellow, you are not getting enough power to the plugs. If the boots and secondary wires are really old, they may be broken inside, or the insulation may be badly cracked, both of which will prevent good spark. The boots are easy to replace. If you do, avoid resistor boots. Sometimes the ends of the wires where they go into the coil can be bad. You should be able to remove the wires (typically there is a threaded cap holding them in) and cut off about 1/4 inch and reinstall. If the wires are molded in, you are stuck with them.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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77 KZ400 runs rough when throttle opened 15 Aug 2016 15:10 #738796

  • mark in Portugal
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agreeing with Texas, and adding;
check that you have good fuel flow. Rust from the tank could be choking fuel supply.

Change the point, plugs, and condenser You have to do that just to rule them out.

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77 KZ400 runs rough when throttle opened 16 Aug 2016 11:40 #738890

  • nodakkz
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Here is an update. I checked the spark here is what it looks like. Looks kind of weak to me... Here is a video of it and a picture of the coil I have. What would you guys suggest for me to do next? Thanks!

Attachment IMG_6122.JPG not found



Attachment IMG_6121.MOV.mov not found

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