KZ400, one carb running rich, fouling plug.

  • Kymasabe
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KZ400, one carb running rich, fouling plug.

10 Jun 2011 02:06
#456457
I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust. We've got the air mixture screw turned out 1.5 turns and tried at 1.25 turns out and makes no difference. Is there anything else I should be looking at?

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  • Nebr_Rex
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Re: KZ400, one carb running rich, fouling plug.

10 Jun 2011 02:13
#456458
Needle and seat leaking?
Float set to high?
2002 ZRX1200R
81 GPz1100
79 KZ1000st daily ride
79 KZ1000mk2 prodject
78 KZ650sr
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81 KZ750e
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77 KZ400/440 cafe project
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  • bountyhunter
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Re: KZ400, one carb running rich, fouling plug.

10 Jun 2011 04:17
#456463
Did you install new inlet valve needles and seats?

I would definitely check the fuel levels in the bowls with a clear tube and adjust as necessary.
1979 KZ-750 Twin

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  • Polar_Bus
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Re: KZ400, one carb running rich, fouling plug.

10 Jun 2011 08:38
#456471
Kymasabe wrote: I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust. We've got the air mixture screw turned out 1.5 turns and tried at 1.25 turns out and makes no difference. Is there anything else I should be looking at?

If everything seems to check out ok with the carb, the next simple check would be a compression check. If you have low compression in that one cyl this will cause a "rich" condition.
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  • treitz
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Re: KZ400, one carb running rich, fouling plug.

15 Jun 2011 17:09
#457441
Kymasabe wrote: I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust. We've got the air mixture screw turned out 1.5 turns and tried at 1.25 turns out and makes no difference. Is there anything else I should be looking at?

I've been working on getting my 400 to run right for a few months now. If you had the mixture screw at 1.5 turns and it was rich, 1.25 turns would be MORE rich. In is rich, out is lean.

At least from my experience and understanding. As you turn it out, you are letting more air into the air/fuel mixture.
1979 KZ400 - 2-1 Manifold - Mikuni VM34

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  • Patton
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Re: KZ400, one carb running rich, fouling plug.

15 Jun 2011 22:21
#457517
Nebr_Rex wrote: ...Float set to high?

Agreed.

If not already done, would perform the clear tube test to assure fuel levels are within specs.

A too high fuel level can result in an excessively rich mixture, regardless of carb settings being otherwise correct.

Good Fortune! :)
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  • loudhvx
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Re: KZ400, one carb running rich, fouling plug.

16 Jun 2011 00:02
#457536
First step is to verify fuel level (as was mentioned).

Second is to verify the jet plug is installed and sealing properly. This is critical on those early Keihins. It's the littl eblack rubber plug that gets held in by the little metal bracket in the float bowl. If it doesn't seal, you get too much fuel.
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  • Tmiron
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Re: KZ400, one carb running rich, fouling plug.

30 Jun 2018 13:07
#786162
wouldn't it just overflow? or would it run rich without overflowing?
1978 KZ400 B1

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  • TexasKZ
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Re: KZ400, one carb running rich, fouling plug.

30 Jun 2018 13:17
#786163
Tmiron wrote: wouldn't it just overflow? or would it run rich without overflowing?
If the fuel level is too high, the mixture will be rich. It will not overflow unless the level is ridiculously high or the float valve is not seating properly.
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  • loudhvx
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Re: KZ400, one carb running rich, fouling plug.

30 Jun 2018 17:47
#786186
If the rubber plugs are missing, it will run rich, but not be overflowing. The rubber plugs do not affect fuel level. They affect flow through the jets.

The fuel float valves control fuel height.

Both need to work properly.
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  • Nerdy
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Re: KZ400, one carb running rich, fouling plug.

01 Jul 2018 11:11
#786225
Kymasabe wrote: I have a '75 KZ400D, we've pulled the carbs, put in new rebuild kits, cleaned everything, and been thru them about 3 or 4 times as we've been battling a running problem with the bike. Seems like the left side carb is running rich, fouls a plug after only 5 minutes of running/riding. Pull the plug and it's wet, stick in a new one and left side cylinder comes back to life, smokes from the exhaust.

What color is the smoke?

blue = burning oil
black = too much fuel/too rich
1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1980 KZ440B
1981 Yamaha XT250H
1981 KZ440 LTD project bike
1981 GPz550
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