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TOPIC: Lean Idle

Lean Idle 3 months 1 week ago #23330

  • Frank833
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Got my carbs back together today. They were on my welding table which I needed to get cleared off to do some welding.

While apart, I replaced the O-Rings, pulled/cleaned the idle air screws (which seemed to be the crux of my issue), did the choke mod (used rivet bodies), checked the float levels (all where perfect) and bench sync'd them (set butterflies with a feeler gauge).

The bike starts well now. But idle is way lean.

The carbs are clean. They had already been "rebuilt" when I got the baskets of parts. I have taken them apart and cleaned them, but other than the idle screws never having been removed/cleaned, they where clean inside. The three little holes for the off idle transition are clean and flow well.

The AFR at fast idle (1200rpm) bounces between 18 and 20. I have an O2 sensor installed in the DG post collector/pre muffler. Tried another O2 sensor and re-ran the calibration, even though it 'acts' lean so I had no reason to suspect an O2 issue.

I have tried going +/- 1 turn on the pilot screws with only modest changes in the AFR.

The relevant bike changes are:

- No air cleaner (I am planning on going with custom filter housing and a 240z Filter240z filter )
- DG 6-1
- 1400cc Big Bore kit

I am thinking I probably just need to go to larger idle jets.

Thoughts?

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Lean Idle 3 months 1 week ago #23341

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Frank. No hands-on experience with re-jetting for a Bore-Kit but agree with the increase in idle-jet size. (One size up...?)
You may also find the need to raise (richen) the main-jet needle 1 notch, as well.

Your final choices/solution/results, will be interesting and informative.
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !

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Last edit: by scotch.

Lean Idle 3 months 1 week ago #23342

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Agree on moving the needle. And will see about the Main. But I am going to get the idle reasonably sorted first. Right now it has a hard time transitioning off idle, but with the idle so lean that does not really mean much.

To save me having to pull the carbs before ordering jets... is stock 42.5? These are the BN/Super BN jets, correct?

And just because posts should have pictures....
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Lean Idle 3 months 6 days ago #23354

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I ordered #50 low speed jets. I skipped all the way to 50 because it is so lean now. The air bleed screws seemed to have about 1.5-2 AFR points of adjustment. So I am guessing that each jet step is something similar. From 20 to 13-14 is a long way to go... 50 is three steps which I am hoping will get me close to 14. It's $30 in jets and shipping for each 'try'.

Have to say I am used to having a box of jets with a wide selection. But when you need 6 of each size, that would be a killer!

It was tempting to order an appropriate size drill set and just drill the existing jets out. But I am sure factory jets flow better/more consistent than ones manually drilled. Especially in these smaller sizes.

The jets should be here by Monday....

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Lean Idle 3 months 6 days ago #23355

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www.kz1300.com/index.php/forum/carburato...vs-old?start=6#20926

Smart move to order NEW jets Frank - drilling-out jets is NOT recommended - Not even to "Test" a theory !

keep us informed - This is interesting !
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !

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Lean Idle 2 weeks 2 days ago #24130

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Got back to this after spending all my free time the last 8 weeks or so racing or prepping for racing.

I think I messed up. The bike idles leaner with the larger jets.

It looks like these jets are metering air, not fuel. So I should have gone smaller.

Can someone confirm?

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