SuzukiSavage.com - Idle A/F screw backing out by itself

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Idle A/F screw backing out by itself
03/11/15 at 15:06:19

OK I did my searches and scanning but apologies if this is already answered. On my ride today the idle kept decreasing and the engine getting 'rougher'. I kept turning up the throttle stop screw to keep it running. My A/F screw was set at 2 turns from lightly seated a few days ago. When I got home from the ride it was at least 10 turns out (but not lost on the street thank goodness). Removing the screw I was struck by how lightly it turned. I was expecting some sort of internal spring under it to keep its threads under tension. Nope, there is just a washer and an O-ring on the shaft just behind the threaded part. Is this screw-coming-out phenomenon something well known? Is there a fix?

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verslagen1 YaBB Moderator ModSquad Offline Where there's a will, I want to be in it. Posts: 28886 L.A. California Gender:	Re: Idle A/F screw backing out by itself Reply #1 - 03/11/15 at 15:22:17 There should be a spring in there too. it may be that due to some cleaners, your o-ring may became mushy too. shouldn't be gummy soft, just a typical rubber o-ring.
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jimthecanoeist

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Re: Idle A/F screw backing out by itself
Reply #2 - 03/11/15 at 16:45:52

That was fast and thank you very much. O-ring looks fine but no spring in there (I can chalk this one up to "the prior owner"). I guess I will take a second look, do some measuring and go find a spring to engineer). This is where I wish for a buddy with the same bike. It would be so easy to note his setting and then pull out his adjuster to see what's behind there.

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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Idle A/F screw backing out by itself Reply #3 - 03/11/15 at 18:42:41 Look at ball point pen springs.. or call Suzuki,, what could they charge? The local hardware store has springs..
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verslagen1 YaBB Moderator ModSquad Offline Where there's a will, I want to be in it. Posts: 28886 L.A. California Gender:	Re: Idle A/F screw backing out by itself Reply #4 - 03/11/15 at 19:06:10 SPRING 13271-93011 $2.74
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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Idle A/F screw backing out by itself Reply #5 - 03/11/15 at 19:40:33 Bingo..
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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 18099 Camp Springs, Kentucky Gender:	Re: Idle A/F screw backing out by itself Reply #6 - 03/12/15 at 03:22:26 Whenever you need to know what you are missing or how things go together....go online and look at a parts diagram. Look at # 41, 42, 43, 44.....you are missing # 42.....the springy thingy. http://www.hondaofflorence.com/fiche_section_detail.asp?section=432120&catego...
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jimthecanoeist

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Re: Idle A/F screw backing out by itself
Reply #7 - 03/12/15 at 11:21:31

Thanks to all. This is a definite "prior owner" fubar. When I took out the screw there was only the washer and O-ring on it. I can see no other explanation except the spring got lost by a prior 'mechanic' and put back without. Months of pain for the current owner (my daughter) who was told about the backfiring - "It is set up for California".
Thank you for the part number and exploded view diagram. I have it bookmarked. Totally knocked out with the response and knowledge here.

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jimthecanoeist

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Re: Idle A/F screw backing out by itself
Reply #8 - 03/14/15 at 11:14:11

modified the lightest ballpoint spring around the house and used to temp assemble while waiting for new spring and O-ring from HSK. No more idle screw backing off but will put in proper spring later. BTW, I hear this referred to as an air screw. Isn't it really adjusting the fuel metering? No big deal but getting my head around backing it out = richer?

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Steve H Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 1223 Spartanburg, SC Gender:	Re: Idle A/F screw backing out by itself Reply #9 - 03/14/15 at 17:50:41 Yes, it is a fuel metering screw. It allows you to fine tune the amount of fuel the pilot circuit supplies to the engine. The idle speed screw on the side of the carb that actuates the butterfly is what regulates the amount of air.
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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Idle A/F screw backing out by itself Reply #10 - 03/14/15 at 18:19:12 I never tried the pen spring, never had a problem with mine,,, glad you won that.
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Dave

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Re: Idle A/F screw backing out by itself
Reply #11 - 03/16/15 at 03:31:05

jimthecanoeist wrote on 03/14/15 at 11:14:11:

BTW, I hear this referred to as an air screw. Isn't it really adjusting the fuel metering? No big deal but getting my head around backing it out = richer?

The stock carb on your bike has a "fuel" screw for the idle mixture. The fuel passes through the pilot jet (with no bleed holes) and is mixed with some air in the carb body, then the fuel mixture screw adjusts how much of that flow goes to the engine.....the fuel screw is on the engine cylinder side of the carb body. Turning the screw out increases fuel flow and makes the engine richer - beyond 3 turns the flow is maximum and it is time to install a larger pilot jet and start the mixture adjustment over again.

The Mikuni VM Round slide that some of us install as a replacement crab has an "air" screw. The fuel passes through the bottom of the pilot jet, and the air enters the sides of the pilot jets through the bleed holes. The air mixture screw controls how much air goes into the bleed holes, and turning the screw out makes the mixture leaner....the idle air screw is located on the air cleaner side of the carb body. The ideal setting is about 1.5 turns out...more than that and you need a leaner jet.

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