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Hesitancy upon take off 1 month 1 week ago #30211

  • McBoney
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Hi all,

Old thread, but still an issue.

I have given her the first 1000 mile service and looking at the oil coming out, all is well.

However, it is still hesitating on idle and running very rich. Exhaust has some baffles in the middle and some small ones at the rear, and I have blocked off two of the four air pods (I have a similar set up as Pete in his pic). I have rebalanced the carbs (they were fine) and attempted to set the mixture using Colortune. I just can't get it lean enough and it idles rough-ish and after a minute or so dies. Oz said to reduce main jets to 105 (?), so that is what I am going to try now, but any other advice, please let me have it.

Above 2000 RPM it runs very nicely indeed, but my exhaust tips are very sooty!

Cheers
Paul
Six-Pot-Cafe in the making...

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Hesitancy upon take off 1 month 1 week ago #30215

  • Kawboy
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Mikuni put out a great write up on setting up jets. if you want to better understand carbs, then you should read this. It's a really good read. (And I should add, the fundimentals are not exclusive to Mikuni's)
Mikuni carb tuning doc Basically, choosing the main jet size comes from running the engine full out hard for 15 or 20 seconds and then taking a plug reading.
Once the main has been selected, deciding on throttle needle sizes and notch positions can be determined.

You're problem has nothing to do with the Main Jets. Pilot Jets and pilot needles are only in operation below 1500 rpm. Float height will have some bearing on the pilot circuit but not as much as its affect on the Main Circuit.
These engines run fine on the stock jets and the needles in the middle notch irregardless of the exhaust options. Period. Scotch has proven this time and time again. He runs a DG pipe I believe and stock jetting. his latest reporting is 52 - 55 MPG (Imperial).
I have yet to see issues with the idle/low speed operation related anything other than either a vacuum leak or problems with the transition ports and I'm talking any carburetted engine and I'm also talking about 300-400 engines over my lifetime. I've been tuning engines for 50 years.

Maybe Scotch will add his 2 cents as well.
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Last edit: by Kawboy.

Hesitancy upon take off 1 month 1 week ago #30223

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1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !
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Last edit: by scotch.

Hesitancy upon take off 1 month 1 week ago #30224

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Further to and very relevant is something I discovered a while back.  "Old" jets with deteriorated surfaces not only disrupt an otherwise smooth and steady flow of fuel but will also cause a disruption to the draw of required "Mixing Air".  This mixing-air is drawn in to the jet tower by the flow of fuel.  The mixing-air port is immediately above the idle jet and the with a correctly functioning Idle-jet, this air presents itself within the jet-tower in the form of a steady flow of uniform  and very small bubbles.  A "rotten" idle-jet disrupts the flow of fuel and creates various size air bubbles at an inconsistent rate which can make adjusting the mixture correctly ......impossible. 
Modifying the pilot screws makes the "adjusting range" of the pilot screws much narrower which in turn makes using a "Color Tune" far more accurate by providing a very definitive "Blue" range.  This eliminates the need to "Hunt" for the "Blue".
1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !

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Last edit: by scotch.

Hesitancy upon take off 2 weeks 5 days ago #30271

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Thanks both,

I have replaced the main jets with 105's and it runs leaner now, also helped by the fact that I closed off two of the four air cleaner pods. Not soo sooty at the exhaust ends.

However, idle is still rough/spluttering and initial take-off is hesitant still. So as the jets were not changed, I will order six new pilot jets and put those in. See what gives.

I'll update when I have done it.

Cheers
Paul
 
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Hesitancy upon take off 1 week 6 days ago #30299

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Ok, I've done some 75 hard miles and this is what the plugs look like now. A little twist in on no 1 and out on no 6 and I think we are there.



However, it idles ok, but taking off and at low revs it is still quite lumpy.... as though running on less than 6 cylinders.

I think I may need to either clean the pilot jets or order a few new ones. 

Considering I have increased the air flow by modifying my air intake to two air cleaner cones, will I need to change pilot jet size as well?

Paul
Six-Pot-Cafe in the making...
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