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In agreement with the points that Easy Rider is making. Am running way behind here but will offer some possibles before getting on with the day.

Checking the air filter is a good place to start as mentioned. A blocked air filter can obviously reduce the amount of needed air for the proper air/fuel mixture. And on these bikes with the EPA gear, it's not uncommon for folks to find that the air filter is saturated with oil. You're correct that black exhaust smoke indicates too fuel rich. Oil smoke is usually grey, but if the oil were excessive, the exhaust smoke would be a blue/black color.

What do the spark plugs look like ? Black, wet & a smell of gas ?

Also as mentioned, if a gravity feed petcock is left open, fuel can continue to enter the carb while the bike is off and eventually find it's way thru the intake and into the combustion chambers. A "vacuum actuated" petcock is only supposed to allow fuel flow either when hitting the starter button or while the bike is running. These types of petocks can sometimes fail and essentially act the same as an open gravity feed type. I forgot to shut off a petcock one time (after that experience, one tries to insure that it doesnt happen a second time). Wasn't getting black smoke, but it did fuel wash the cylinder bores and the excess fuel got into the crankcase, which diluted the oil. Potentially disastrous situation unless caught in time. You could probably remove the oil filler cap and see if you get a whiff of gas or not.

I realize that we touched on possible choke probs earlier in the thread and we both agreed that the choke seemed to be working properly. We might want to revisit that as a possible at least.

As Easy Rider points out, the needle valve might not be cutting offf the flow of fuel into the float bowl. Also not uncommon if the needle valve seat o-ring has deteriorated.

This is a real long shot.........the old Triumphs have a main jet holder that's removable. Had one vibrate loose completely, which essentially negated the main jet. Point being, it's rare, but at least possible for jets themselves to come loose. If by chance the pilot jet were loose, one can imagine how much more fuel could be getting dumped into the mix.
 

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Discussion Starter #22
Ok, pulled the carb again, dismantled, cleaned again. Checked the plug. Had some carbon but nothing close to fouled. Cleaned it. Now I can get it to idle fine, but choke needs to be pulled out to first click to run. Starts fine with choke all the way out. Dies if pushed all the way back in. First notch while pulling back out, it will keep running. No more black smoke. I suspect that the fuel level in the carb bowl is too low. Raising fuel height is my next course. Am I assuming correctly?
 

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don't want to beat you up over this, but when you clean the carbs do you blow carb cleaner thru all the passages and can you see light when you hold the jets up and look thru
 

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https://www.partzilla.com/catalog/suzuki/motorcycle/2006/boulevard-s40-ls650/carburetor i looked on partzillafor a 2007 s40. the parts diagram says for part #18 pilot jet it's 52.5 and the main is 45. in your previous posts has 55 pilot and 150 main.your having problems in the low rpm range but if it runs better with the choke one quarter out and i'm suggesting your pilots to rich doesn't make sense. the other thing is i'm not an expert on carbs so here it is, wouldn't a low float bowl affect wide open throttle where the demand on fuel is greater than low rpm's
 

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This is interesting. Before pulling/cleaning the carb this last time, it seemed like the symptoms indicated a too rich condition. Now it appears to be a bit on the lean side. If you removed then re-installed the choke plunger during the carb cleaning, guess it's possible that the choke plunger might have been off somehow and it got corrected during re-installation ?

You're right, Nick, about the float level having more fuel demand at higher rpm's altho' at idle there would be at least some demand for a proper idle. With the bike running, the vacuum pulls fuel into the venturi, creating a mist for the air/fuel ratio. Lower rpm's, less vacuum, demanding less fuel. Higher rpm's, higher vacuum, demanding more fuel. Would think that if the float level is at factory spec, that part would be good to go.

Your stock jetting of 52.5 pilot, 145 main should be fine. Having to open the choke 1/4 way out would indicate a need for more fuel. Also, when you open the throttle, it lifts the slide/piston inside the carb body which allows more air into the venturi. More air when it's possibly too lean to begin with may be causing the prob when opening the throttle.

Earlier, you mentioned that the air/fuel mixture screw was 1 1/2 turns out, with factory spec calling for 3 turns out. You might try turning it out to factory spec to see if that provides the needed fuel that the choke is currently compensating for. It might also allow the proper amount of fuel to balance out the mix when opening the throttle and having the slide allow more air in. You're CLOSE and might nail this down soon. Keep up the good work!
 

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Discussion Starter #28
I've gotten pretty good at pulling the carb. Lol. I just pulled it off again, took it down to everything that can come off, clean it out, every passage and orifice. One of the jets up top, under the diaphragm may have been clogged. Looks like a new carb now. Checked float height at a hair over 1 inch. In spec. With clear tubing, checked fuel height. Just under top of bowl. Within 1/2 cm. Fuel flows freely through petcock. Everything is totally back to stock. That's where I quit. Will see what happens tomorrow. This has been a real head scratcher. Thanks for all the input..
 

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Will see what happens tomorrow. This has been a real head scratcher. Thanks for all the input..
Sounds like you have now gone from WAY rich to a bit lean......which is normal for late model bikes.

First, be sure you have the air filter ON, that there are no manifold vacuum leaks, and let it warm up good before you convince yourself that there still is a problem.

It is normal to need one click on the choke for it to idle cold......and maybe another click if you want to actually ride it before it warms up good.
 

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Discussion Starter #30
Yesterday when I could get a good idle, I let it run for probably 5 minutes. Good and warmed up. Still wouldn't run if the choke pushed all the way in. Anyway, gonna try again today
 

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There's no shame in farming it out. I'm about to do the same with a project that's been beating me up, more than tired of beating my head against the wall. To your credit, you've given it your best shot in spite of the ever present frustration. While thinking about your situation and trying to figure it out in my head, the solution continues to stay hidden from us. Something's not cooperating, but what is it ???

Not gonna try to talk you out of your decision because I know this has been frustrating beyond words. Only out of curiosity and nothing more, did you try turning out the air/fuel mixture screw more than the 1 1/2 turns that you mentioned earlier ? If that didn't do it, I'm out of ideas as well. One way or another, it'll get done and you can move forward again from that point on.
 

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Discussion Starter #33
Yeah, I've tried multiple screw setting. About to wear the starter out. The really frustrating thing is, I got it to idle nicely yesterday. Can't even get it to start today. Got friends at the Suzuki dealer down the road. They've fixed bugaboos for me before. One of these days I will post pics of the project. Thanks.
 

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Sounds like a plan. The best course of action when a mechanical issue hits the wall is to put down the wrench and simply walk away. Patience never having been one of my strong points, it took me quite awhile to figure this out. LOL!

And as you well know, getting in the wind does wonders for clearing the head. ENJOY the day and Ride Safe............
 

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Pulling out choke to first notch got the bike running without problem, but it won't run once warmed with choke disengaged. Sounds like it may be related to your rejet job, sounds like it needs to be set richer. Yes, a pro mechanic familiar with rejetting bikes with modified exhausts would be someone to help.

Sorry, can't be of much help as I've never rejetted a bike. I left my 1987 Savage with stock exhaust and with the sea level jets ran fine at the higher elevations, even 8,000 feet. It had enough torque to pull stumps, a really fun bike on the rural back roads. Some years back, showed up at a rally in Chama, NM 8 hours and 400 miles away, got comments about being a "real" biker and how I could "ride such a tiny thing".
Then I'd remind them that a 650 was a big bike in the 1960's and 1970's.:lol4:

Hope you get it all sorted out, you'll enjoy "living the legend" on your S40, a real fun, no nonsense bike. :bluethum:

Oh, and BTW, I installed a Drag Specialties electronic mini-tach for a 2 cylinder Harley-Davidson on my Savage. It worked perfectly. The LS650's are double fire ignition (fires every crankshaft revolution), why it worked. This is the accessory that Suzuki left off. I found it very helpful to select my shift points, and watch my rpm's on the open highway. Also, it served as my speedometer when its cable broke, until I could repair it. My wide ratio 4 speed transmission gave me 5,200 rpm at 75 mph, only 1,300 rpm less than redline at 6,500. Your S40 with 5 speed is about 300 rpm lower than mine.

Another caveat to the 650 single is that when the weather is very hot, you'll use more oil. This is not oil burning, just the nature as this air cooled runs hotter than the water cooled's. I'd be adding about a 1/4 quart every other fill up when temps were above 95 deg F. At cooler temps below 75 I would be hardly adding anything. Some have ruined their valve train by not maintaining proper oil level on rides. (Heard the same about the Kawasaki KLR650, which interestingly is a water cooled.) Anyway, FYI.
 

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Discussion Starter #37
My friends at the shop set me straight. Turns out I did not have the required washer on the main jet and I had the spacers on the wrong side of the jet needle c clip. Oh, dopey me! Anyway, they are in the process of setting me up right with a proper jet kit including tapered jet needle. The S40 comes from the factory some what neutered, running very lean. I already knew that, but did not appreciate that more was needed than just a jet swap. So, I'll be able to post pics soon, but we're supposed to get more snow so may be a while. Thanks for all the input. Now, if you see another in my predicament, here's some items to point out.:D
 

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That's GREAT news! Your buds did right by you. The causes they found explain why we were scratching our heads in not being able to find the solution. Congrats!

Not disputing your buds suggestion to re-jet, etc........just find it interesting that the re-jet is necessary when just changing the exhaust and keeping the stock air box. Oh well, live 'n learn. It's all good.
 

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Not disputing your buds suggestion to re-jet, etc........just find it interesting that the re-jet is necessary when just changing the exhaust and keeping the stock air box. Oh well, live 'n learn. It's all good.
Re-jetting is necessary when changing exhausts, when there is a change in back pressure. A reduction will require en-richening the fuel mixture, because reduced back pressure will cause the bike to run lean. To meet emission standards, the bike is already lean tuned. Putting a less restrictive, freer flowing muffler without carburettor adjustments will cause the bike to run further lean, not good.
 

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Agreed on the need for the proper back pressure. Phil mentioned that he eliminated the muffler by using a slip-on. Depending on the shape of the slip-on, his back pressure was either retained or compromised, sometimes even lost entirely. I've had good results in maintaining back pressure when using EMGO Shorty style slip-ons, even when removing the baffles they come with. No re-jet required in 3 different machines. Running straight-thru SE1's slip-ons on the Harley and did have to enrichen the mixture via adjusting the air/fuel mixture screw, but no re-jet.
 
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