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Message started by TheCaliKid on 09/16/08 at 18:56:59

Title: Help with S40 Backfire fix
Post by TheCaliKid on 09/16/08 at 18:56:59

Hi All,
I have just bought my first bike, a used 2007 S40 with 2800 mi. Loving it except for the backfiring. I enjoy the odd one here & there, but I live in a hilly area and when engine braking on steep ones it gets annoying. I would like to adjust the fuel/air mixture, but I need some detailed instruction. Brass plug on the RH side? Drill it out? Which direction to turn screw? etc.
Thanks,
Mike

Title: Re: Help with S40 Backfire fix
Post by YonuhAdisi on 09/16/08 at 19:29:45

Check out this thread. It is the index for the tech/ref section of this site.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1181745927

Title: Re: Help with S40 Backfire fix
Post by verslagen1 on 09/16/08 at 20:30:47

also check the torque on the header bolts, 15 to 20 ft-lbs on a cold morning, no start till checked.

also check the muffler clamp, anytime, but I suggest cool to the touche. :o

Where are you?

Title: Re: Help with S40 Backfire fix
Post by firetruckredbike on 09/17/08 at 03:00:05

I just took Thump in for scheduled maintenance / tuneup and now the backfiring is gone. *weeping* I liked his little backfiring. It was useful when someone was following too closely, and I also truly enjoyed his final comment when pulling him into the garage for the night. But to each his own. :'(

Ride safe,
Amy

Title: Re: Help with S40 Backfire fix
Post by TheCaliKid on 09/17/08 at 07:25:50

I'm in Hollywood CA

Title: Re: Help with S40 Backfire fix
Post by verslagen1 on 09/17/08 at 07:31:08

I work in beautiful downtown Burbank, you have any troubles...

Title: Re: Help with S40 Backfire fix
Post by up4fishin on 09/17/08 at 17:49:28

good links to the tech reference site, but the step by step for the brass plug removal could use some pictures. seems different people have different techniques. also seems people drill too deeply and mess up the screw under the cap. pics of a successful removal would be really helpful. thanks! :-/

Title: Re: Help with S40 Backfire fix
Post by TheCaliKid on 09/17/08 at 22:16:11

Thanks for suggestions. The bike has been down a few times compliments of prevoius owner, so maybe the Header/muffler do need a tweek. I don't have many tools (ei. Torque Wrench), and am a bit afraid of damaging the bike by drilling etc. I've only had the bike 2 weeks, and I'm guessing like most others out there, I'll be dabbling soon...

Title: Re: Help with S40 Backfire fix
Post by John Winston on 09/18/08 at 13:50:07

Ok Calikid ...here's what you do for that backfire. You are going to need a drill and drill bit, large screw, large screwdriver, pliers and small screwdriver. here's what you do ... Drill the middle of the brass plug on the right side of the carbureator ... do not just send the drill bit thru because you do not want to damage the gas adjustment screw behind the brass plug. You want the hole just big enough for the large screw ... with the screw and large screwdriver turn it into the hole you have drilled ... you want to just get the screw stuck in the brass plug but not go all the way thru to damage behind it. Get your pliers, grab hold of the screwhead, leaverage yourself and pull the brass plug out. Take your small screw driver and turn the adjustment screw a half a turn counterclockwise ... stop. That's it.
I have the 2007 stock bike ... pipes and carbureator and did this adjustment ... the engine and muffler runs and sounds so much better.

Good luck.

Title: Re: Help with S40 Backfire fix
Post by 07S40rider on 09/18/08 at 14:30:38

My understanding, from reading what seems like hundreds of posts about the air/fuel mixture screw and the brass plug, is that from the factory the S40 is set for maximum fuel economy (super lean maybe?) and while adjusting the A/F mixture screw will correct the backfiring - it also will most likely cause gas mileage to decrease. Correct? If so, given current gas prices I thought this might be something CaliKid would want to be aware of. If I am incorrect, please straighten me out before I spread this crazy propaganda any further~! ::)

Title: Re: Help with S40 Backfire fix
Post by John Winston on 09/18/08 at 15:01:00

The brass plug is meant to keep you from adjusting the lean setting ... when you hear and see the difference from the minor adjustment I explained YOU WILL LIKE IT ... the engine and muffler sounds like it is supposed to be. My judgement ... and take it for what it is worth ... you want your bike to run like this and not on the lean setting. If you feel uncomfortable with the adjustment ... just turn the screw clockwise a half a turn and you are back where you started. I have not gauged the gas factor after the adjustment yet ... I can tell you I will not set it back to run like it was on the lean setting. I am not a technical guru like the others here when the talk about in the long run your bike running lean makes it run hot ... and will wear out parts sooner. The bike runs better with the minor adjustment ... the tech at the dealership shop told me this is what he does when customers complain about the backfiring. I did it ... I love it ... I put the information here if anyone wants to try it.

Title: Re: Help with S40 Backfire fix
Post by verslagen1 on 09/18/08 at 15:14:47

True Mikuni stated that mpg is dependant upon the idle jet setting as once a sable speed is attained, the throttle setting will be in the range of the pilot jet. Which explains why even though I've gone up a couple of sizes in the main jet my mpg hasn't changed alot.

For best carb adjustment procedures, see the tech section. ;D

Title: Re: Help with S40 Backfire fix
Post by EssForty on 09/18/08 at 18:24:05

656B6E696C6D7A080 wrote:

It's documented on my blog with pictures that should answer all your questions. It is really an easy mod to do.

Here's the link:

http://essforty.blogspot.com/2008/09/idle-mixture-screw-adjustment.html

Title: Re: Help with S40 Backfire fix
Post by justin_o_guy2 on 09/18/08 at 19:20:28

I was in the shop the other day, just shooting the bull;, hanging with the mechanic. He was going thru some carbs. Grabbed his drill, poked a little hole in the brass cap, then reached into his toolbox & grabbed a plastic box with odd tools in it. Came out with a drywall screw, set it in the hole & torqued it with the screwdriver, grabbed a pair O dikes & found a good spot on the carb for a fulcrum & lebered it out. Easy Peeeasy! Just dont be pushing on that drill. The cap is thin. Be ready to yank back on the drill & some tape wrapped on the bit will help stop it, too. Just 1/8th back from the tip, a few wraps..

Title: Re: Help with S40 Backfire fix
Post by EssForty on 09/19/08 at 02:44:53

That's exactly how I did it. Here's the pics of drilling, then the drywall screw in the brass plug, then the screw adjustment.

http://4.bp.blogspot.com/_2NU0p82vl5Y/SNL8XpdlbBI/AAAAAAAAADo/S8o1YoKEm9U/s320/DSC_0018-1.jpg

http://2.bp.blogspot.com/_2NU0p82vl5Y/SNL9WoJH5tI/AAAAAAAAAD4/7n8P69S7OiI/s320/DSC_0020.jpg

And then this shows the exposed idle mixture screw being adjusted.

http://2.bp.blogspot.com/_2NU0p82vl5Y/SNL9xpurtlI/AAAAAAAAAEA/YEjeh9P5q90/s320/DSC_0022.jpg

I documented it in more detail on my blog since I had to post the pics there anyway. I've also posted it in the tech docs section as well since I did not see any pictures in the existing thread.

http://essforty.blogspot.com/2008/09/idle-mixture-screw-adjustment.html

Title: Re: Help with S40 Backfire fix
Post by T Mack 1 on 09/19/08 at 05:47:53

0403670004465D505146340 wrote:

No, the mixture was set for pollution emissions off the factory floor. Being lean to the point of becoming inefficient. Inefficiency means that you could get a tiny bit more mpg by adjusting it a tiny bit ....... key word.... tiny bit...

For most, the "fun" factor takes hold and most people tweak it to most instant power (means centered or slightly rich)........ AND then "fun" factor causes more WOT and that lowers MPG....

Note: the super lean tune will, over time, cause the engine to start polluting more as the parts get damaged from the extra heat produced..... but it passed the EPA std's when made... Now, I will say that it is a very fine line to get the perfect tune, and most people don't have it perfect. I know mine is running slight rich...... avg city riding 47-49 mpg.

Title: Re: Help with S40 Backfire fix
Post by up4fishin on 09/20/08 at 18:21:17

thanks EssForty--these pics pushed me over the edge and I took the plunge.

i backed out the screw 1/2 turn from it's original setting per your directions and observed no change. now it is out a full turn and still backfiring. do others on this site have a comment about how far out to back the screw? my bike is an 06 in case that matters. thanks.

:-?

Title: Re: Help with S40 Backfire fix
Post by serowbot on 09/20/08 at 19:38:32

only to say, as you probably already have read elsewhere, that you don't want to be more than 3 full rotations out. Any more than that and you risk the screw coming loose. To reduce the "backfire", which is really an afterfire, you might also try increasing the idle speed a little. See if that helps....

And,..an afterfire is a "ka-bang!" kind of gunshot sound.
Little "whump,..pop..blat...wooble, wooble" sounds on deceleration are normal for a big thumper, and are harmless, and kinda' cool.

Title: Re: Help with S40 Backfire fix
Post by BurnPgh on 09/20/08 at 20:18:15

try turning the idle down when tuning the mix screw. If I had my idle at the spec RPMs when tuning it made no appreciable difference in engine speed. I only got it tuned after someone told me to turn the idle down.

Title: Re: Help with S40 Backfire fix
Post by mick on 09/20/08 at 20:30:41

I got mine screwed out one and a half turns,it still backfires,but runs great :)

Title: Re: Help with S40 Backfire fix
Post by seviersavage on 09/20/08 at 20:58:15

I think the white spacer mod in combination with the idle mixture adjustment made the real difference for me.
Seviersavage

Title: Re: Help with S40 Backfire fix
Post by Oldfeller on 09/21/08 at 03:58:27

Clarify the start solenoid adjustment conditions, please. Too tight is ???? Too loose is ???? Solenoid adjustment doesn't play, mis-assembly was the culprit. Reason why this is so ????

Your post is interesting, but I cannot connect it to the "normal" solenoid adjustment parameters which may affect many bikes.

Title: Re: Help with S40 Backfire fix
Post by EssForty on 09/21/08 at 04:36:10

Deleted prior post suggesting it may be related to the decompressor linkage. I had backfiring due to misassembly so it may not be a good example. If he is in the normal range of play it is simple enough to rule out by checking it. I would not have normally brought it up, except for the fact that it mirrored some of his symptoms.

Also, after I figured it out, I did find a good writeup of the decompression linkage assembly on page 92, whereas I was working around page 55.

So . it may not be relevant at all, but you never know. File it under "stupid things you can do to make backfiring worse" ;)

Title: Re: Help with S40 Backfire fix
Post by coachchuck on 09/21/08 at 22:14:51

I bought a 2005 S40 on September 12. Very nice motorcycle with low mileage and no corrosion. Made purchase with no test ride (cautious seller). Have put on 150 miles since purchase and very happy. But noticed the backfiring. Started research, including this site. Today, I removed the brass plug and adjusted low end mixture. Also, removed the spacer on the slide needle. All went well.

I removed the brass plug by drilling it out with a drill bit slightly smaller than the casing around the plug. I was careful not to let the drill bit touch the head of the adjustment screw. It really was a 'piece of cake." By the way, there was a small hole in the middle of the brass plug. I stuck a needle through the hole and determined that there was about a 1/4 inch space between the outer face of the plug and the face of the adjustment screw.

As suggested, I turned out the low end mixture screw until idle speed peaked. A half turn counterclockwise. During test drive, noticed an increase in power and smoothness in acceleration. Backfire is less but still offers a minor "pop" now and then just to let me know it's still happy. :)

Other than having to remove the seat and the tank, this was an easy fix. No need to remove the carb. Just be careful working in and around the diaphragm, especially during replacement of the spring and cover.

:oTwo day later - In my previous post, I recounted my "success" with removing the spacer on the jet needle and adjustment of the idle mixture screw. In the past two days, my "success" has proven less so. My engine started running lean, not rich! Yes! That's correct! Leaner! More pronounced backfires and weak acceleration, especially from idle. I progressively richened the idle mixture with no improvement. So, today, I replaced the spacer (Smart not to have thrown it away!) and now it runs just fine. And the idle mixture adjustment seems to make a substantial difference. Consequently, I don't recommend removing the spacer. Leave it alone. BTW, the brass plug in my carb was 9/64 thick.