Re-tuned Idle Mix, Hesitation When Rolling On Throttle - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 5 (permalink) Old 07-16-2018, 10:12 AM Thread Starter
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Re-tuned Idle Mix, Hesitation When Rolling On Throttle

I've had my bike for 2k miles now. I haven't had any major running issues with it. Some suspected POOGs that was actually an electrical problem combined with the lean-running tendency of a low gas tank. Otherwise it starts and runs well. It pulled well and was quite drivable. If I was really picky, it seemed slightly reluctant to come off idle. I'd describe it as the following sentence, where | marks cracking the throttle.

putt-putt-putt|pow-pow-poW-POW-POW-POW

It would take about 3 revs for the power to kick in and rev up off idle. I just chalked it up to the characteristic of a CV carb, having never owned a CV carb engine before.

I decided to re-tune my carbs since I'm running open pipes after the goat. I suspected I might be slightly lean from the removal of the baffles (well, entire mufflers). My front carb was at 2.5 turns. My rear carb was at 0.5 turns!!!

So I re-tuned them by adjusting both to 2.5 turns as a starting point. Warm/hot engine and no choke. I then adjusted both a half turn in the same direction and listen for a rising idle. (I should state that I used 1500 as idle speed, so that I had a line for the Tach to point to. This made it easier to detect rising/falling idle). I found idle peak was between 3 and 3.5 turns. My second test was to crack the throttle and listen to the characteristics as it settles back to idle. If it dropped below idle and recovered, it's lean. If it was slow to come down, it was rich. 3 turns was the quickest fall, with 3.5 turns being a bit slower to come down. I settled on 3.5, to err on the side of being rich. I am still (to my knowledge) running stock slides/shims/jets. I readjusted the idle speed to 1200 after tuning.

The results:
Cold and hot starts have improved. Throttle response off idle has improved.
(putt-putt-putt|poW-POW-POW-POW). It pulls well (perhaps better? Hard to say). The only thing is now when I'm coasting and roll the throttle back on, it hesitates before power comes back on. I also notice it during leisurely gear changes. Quick gear changes don't have this. It's only when I'm off the throttle for 3/4 second or more, and reapply, that I have this.

Too rich?

Side note, my friend says that my exhaust smells better now, or rather smells less. He said it smelled bad before. He couldn't describe it other than to say that it was "bad" and wasn't rich smelling.


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
22490.0+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
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post #2 of 5 (permalink) Old 07-20-2018, 02:17 PM Thread Starter
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Anyone?


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
22490.0+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
post #3 of 5 (permalink) Old 07-20-2018, 02:31 PM
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Hard to say, I can't remember how exactly an at-speed fuel mix test would run, especially with a CV carb. Is the fuel mix behaving well otherwise?

Earshave+Rejet (38/135) NGK Iridiums MCCT Conversion Slipstreamer S03 Windshield Custom Extended Backrest Custom Highway Bars MOSFET R/R LED Underglow Volt+USB In-Dash Two-Wire & Blue-Wire Mod Satin Black Engine Paint Dampers Parts - Jets: Main=99101-393(#132 stock)/Pilot=n424-22 Pilot(#38 stock)
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post #4 of 5 (permalink) Old 07-20-2018, 03:24 PM Thread Starter
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It otherwise seems to run well.

Strong pull from idle to 8500 rpm. Steady idle. Good throttle response coming off idle. Transition from part to full throttle is fine. Easy hot starts. Reasonable/expected use of choke on cold starts.

Only issue is the transitioning from decel/coasting, to throttle, has hesitation.


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
22490.0+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
post #5 of 5 (permalink) Old 07-20-2018, 06:33 PM
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Dirty pilot jet(s)? Makes transition to the main jet horrible. You twist the throttle, nothing much happens except it gradually builds rpm, then the power comes on all at once. It's a lot worse if the pilot is completely plugged off.

Also check the slide diaphragms for leaks/cracks. If one is slow to react, it can cause hesitation or even bogging out if bad enough.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
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Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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