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 Air screw sync question

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1Wingman1
Maxi-Scooter Rider
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Number of posts : 125
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PostSubject: Air screw sync question   Air screw sync question I_icon_minitimeSat Jul 09, 2022 9:48 pm

I want to know if anyone knows the set point (number of turns from fully screwed in) for the #1 screw that the Honda factory uses.  I understand fairly well how to make the adjustment and have vacuum gauges and experience on mostly 4 cylinder bikes so I am not looking for detailed instructions.  Thanks for your knowledge.


Edit:

I am trying to improve a rough idle problem and have tried all the conventional remedies. The adj. procedure on 5-61 of my manual seems to me to mean that the screws will be turned out 1.5 turns or less. I found both of mine at 2.25 turns. I tried turning both in equally after balancing with gauges but I couldn't perfect the idle. At this point I think that one must simply set #1 screw wherever the best idle can be obtained with #2 in balance without regard for the number of turns.
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zrx212
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeSun Jul 10, 2022 1:56 pm

Unlike other motorcycles the SW synchronization is air bleed or bypass throttle valves, not mechanical, the recommended 1.5 turns limit is probably to meet emissions specs., etc. They where probably set at 2.25 to give a better transition, i.e. less lean mixture ??, is kinda catch-22 because you have to compensate with idle screw, I can remember exactly my settings, but the #1 throttle body A/S should be considered the base/master, set both to air screws to same X number of turns, then only use the only the other T/B air screw to balance, then adjust idle as necessary, don't move #1 A/S. I used my old mercury sticks, just adjusted to be balanced, no actual vacuum reading, IAC the difference in position of air screws was hardly noticeable, mine idles great at approx, 1300rpm, changes slightly depending on OAT, but is very steady.
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zrx212
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeMon Jul 11, 2022 1:20 pm

Well, out of curiosity/boredom decided to synch my throttle bodies, both my screws were previously set at approx. 2 turns, initial balance was withing 10mm on mercury balance sticks, after fully warming up scooter to "fan on/off" and with a box fan to cool down. Made a reference mark with a fine point sharpie at 1.5 turns on throttle body, then reset both airscrews at 1.25 as a starting point, IOW under the 1.5 turn limit to have some adjustment range. Had to turn idle screw in/up about 1/8 turn after starting, as idle was low.  I only adjusted the left screw very slightly to match right cylinder a close as possible. As final adjustment, I opened both screws another 1/16 inch (re-checked balance), still below the 1.5 turn limit/reference mark. Removed mercury sticks, restored, etc. and adjusted idle slightly to 1,300.  
Idles better and runs/drives good Cool

Air screw sync question Img_2010
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1Wingman1
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeMon Jul 11, 2022 8:18 pm

I started tweaking mine again today. I was very surprised to learn that the Silver Wing will idle fairly well with both air screws fully closed. There must be some extra passages. I now have a pretty good idle with #1 at 1 7/8 turns and #2 at 1 3/4 turns. I could not work it out below the 1.5 reference.

Thanks zrx212 for your help.
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zrx212
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeMon Jul 11, 2022 10:20 pm

" Silver Wing will idle fairly well with both air screws fully closed. There must be some extra passages. I now have a pretty good idle with #1 at 1 7/8 turns and #2 at 1 3/4 turns. I could not work it out below the 1.5 reference. "

Yes, I actually had both screw all the way closed at one point also scratch, even though mine where set lower the difference/spread was almost identical at 1/8 inch, I just raised/adjusted my idle back up slightly with idle screw to compensate, IAC did a longer 15mi road test thru some traffic is all good. Idle is very smooth/steady. Doing a long trip soon will see if it affects mileage, etc.
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Terry Smith
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeTue Jul 12, 2022 12:39 am

The engine idle speed is controlled by how much air enters through the various passages. At idle, the butterflies are fully closed and idling air comes via the bypass system. The idle screw and the fast idle wax unit control one air bypass passage, and the balance adjusters have a separate bypass passage. So you could possibly have the balance adjusters mostly closed and the idle adjuster more open, or the balance adjusters more open and the idle adjuster closed down a bit, and have the same amount of air entering the engine.

The image is of the system on a VTX Honda but the general layout will be the same.
Air screw sync question Vtx10110


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zrx212
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeTue Jul 12, 2022 7:36 am

That's a great explanation and diagram, sometimes the Honda shop manual is "kinda" lacking on info/clarity, that diagram should be on all shop manuals IMO, I do believe that the limitation of 1.5 turns on air screws is for a reason, maybe it predetermines the position of throttle plates at idle to fall withing the values the "TPS" and/or other sensors are looking for ??
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Pindar
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeTue Jul 12, 2022 11:07 am

Quick question, which of the two is #1 air screw adjustment ...... Ref as if sitting on bike....thanks
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1Wingman1
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeTue Jul 12, 2022 2:14 pm

Cylinder numbering is done left to right as you are on the seat. Therefore, I called the air screw on the left #1 as you sit on the seat. I dug around in manual some but could not prove it.

To zrx212: I decided to plunge in a little deeper and found that I have less than 1/2 the amount of fuel flow that the book calls for. I will work on that and then my idle might improve. I will test the fuel pressure to make sure the pump is up to par and then I might need a fuel filter to eliminate some restriction to the fuel flow. I have a group ride tomorrow during which I can use up some of the fuel in the tank.
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zrx212
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PostSubject: Re: Air screw sync question   Air screw sync question I_icon_minitimeTue Jul 12, 2022 3:30 pm

" Cylinder numbering is done left to right as you are on the seat. Therefore, I called the air screw on the left #1 as you sit on the seat. I dug around in manual some but could not prove it. "

Ditto here, but really as both throttle valves are attached to a single common shaft, there's really no master IMO, IAC is 360 crank engine, pistons move together, loss spark/single ignition coil.

IME on most engines with overhead cams the #1 cylinder is next to timing chain sprockets, RH side on SW600, where you will be able to easily see the cam lobes position, alignment marks, etc. for ease of assembly.

Check the fuel pressure regulator(FPR) vacuum hose, cap off at manifold and apply vacuum to FPR with a brake bleeding tool, etc. to see if it holds vacuum and if idle changes while running. Worth checking before tearing into fuel tank, Good luck.
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