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Discussion Starter #1 (Edited)
Just joined this site. I just modded a 2006 Suzuki S40. Muffler elimination with slip on. Rejet with 150 main. 55 pilot. Now I can't get it to start. Will turn over and occasionally fire. Maybe even run for a couple secs. Opening throttle kills it. Battery is good and replaced spark plug. Good spark. Fuel flow good. Fuel in carburetor bowl with in half centimeter of top. Should mention that bike ran before mods. I have a Suzuki dealer up the street but would love to solve this myself.. Currently own 2008 C90T Boulevard, and 1974 Kawasaki F9 (aka Bighorn 350).
 

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Certainly sounds like it's too lean.
Since you've had the carb apart, there might be an air/vacuum leak somewhere.

You made no mention of using the choke or of having a stock air filter in place.
Both probably are important.

It usually is NOT necessary to re-jet just with a change to the pipes.
 

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Discussion Starter #3
Choke is out. Stock air filter. Where should I look for vacuum leaks. I like to think that I was meticulous in carb work, but maybe I overlooked something?
 

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Agreed on normally not having to re-jet when just changing pipes, especially since you've also kept the stock air filter. I'm guessing that with the re-jet, it's now too rich.

You might try putting the stock jets back in and see if that does the trick. If it fires normally, you might getting some minor exhaust popping, usually on decel, but that can often be alleviated by adjusting the air/fuel mixture screw.
 

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Discussion Starter #5
Ok. Just put stock jets back in. Fired up but won't idle. Runs with throttle open , main jet takes over. I had lost the idle mix screw and picked one up from my friends at the Suzuki dealer. Could I have the wrong screw even though it looks like the old one? And would that be the problem?
 

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When you cleaned the carb and were intending to re-jet, did you place the stock pilot jet aside without cleaning ? If so, it's possible that it's got sediment in there blocking proper fuel flow for idle.

There's usually an idle adjuster thumb-screw (small, round knob for turning in or out) and a seperate air/fuel mixture screw. Typically, the air/fuel mixture screw is pre-set from the factory and covered with a blanking plug, usually small round brass plug, so's we don't try to adjust 'em ourselves. If your's is still blanked, then that shouldn't be an issue. IF the blanking plug has been removed, then it's definitely possible that the air/fuel mixture screw needs to be dialed in again. If that's the case, turning it in until j-u-s-t lightly seated and then backing it out 2 turns (usually) is a good ball park setting to start from. (More on this later if this is the case)

If the idle mix screw you're referring to is the idle adjuster thumb-screw, can you turn it clockwise or counterclockwise to achieve a proper rpm idle ?
 

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Discussion Starter #7
Jets were cleaned and inspected prior to installation. Like I said, stock fuel air screw was lost. Installed one I got from dealership that looked correct, but maybe not. Turning it seems to make no difference
 

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Just covering the bases here, new mixture screw had the friction fit O-ring, yes ? Other than going back to the dealership to insure getting the right one, are you sure that the choke is working properly ? If it's hanging up and not closing when supposed to, that excess fuel from the choke being open could interfere with the mixture screw's ability to adjust.
 

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Discussion Starter #9
O ring and spring, yes. Pretty sure choke is working properly. Starts with it out, only runs with throttle open when pushed in. Black smoke on start up, rich? Bike only has about 4000 miles. Never burned oil or smoked before., I'll be visiting the dealership tomorrow. They're good and have helped a lot in the past. Just hoped I could resolve this
 

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You're right, it does sound like the choke is working properly. The black smoke would indicate rich, but that might be related to the funky mixture screw and should be fine once that's sorted out. You should be able to resolve this yourself once you've got the right mixture screw and can pick the brains of the dealership crew tomorrow to see what else they might add. Good luck & please do keep us posted.
 

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Black smoke on start up, rich? Bike only has about 4000 miles. Never burned oil or smoked before.,

Some folks get upset when I advise people with no prior training or experience against messing with their exhaust, intake or carbs.
But THIS situation is a big part of why I do that.

More of those operations go bad than you might expect because a lot of people are embarrassed to admit that it went bad.

I hope that you get things running again.
And I hope you are pleased with the end result.

I've been doing this bike thing for about 50 years now and have NEVER heard a thumper with straight pipes that sounded good (meaning any pipes without true baffles).
 

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Discussion Starter #14
Thanks again all. I picked up this S40 for my son to ride but he kinda lost interest. I decided to play with it after seeing Ryca kits. So, I changed the contour of the seat, which I find incredibly uncomfortable, with the help of my wife who can upholster anything. Bought some "standard" handle bars on Ebay for $10, bought a no name stainless steel slipon with baffle (not much of one IMHO), and removed muffler and wrapped the pipe. I may relocate the foot pegs later, but that's a maybe. Anyway, I'm doing this for fun. I do like the way the bike handles except for the stock drag bars, and now with wider bars and higher seat, it at least feels better even though I haven't ridden it yet. Jetting mod was a suggestion I'd seen elsewhere. I have done a top end and carb rebuild on my 74 Kawasaki F9, but that's a 2 stroke and different animal, and my daily ride is a 2008 Suzuki C90T which is unmolested except for Mustang seat and 4 inch handle bar risers. Will post results soon. Thanks again!
 

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You've seen the Ryca kits so you already know that a lotta folks are building some very nice looking bobbers, cafe racers and even scramblers from the S40 platform. Don't blame you one bit for having fun with it since it ended up in your stable anyways. Almost bought a 1987 about 10 yrs. ago, when they were still called the Savage. The potential for building a bobber out of it made it real tempting and the price was right ($800)

With the way of the world these days, we have to find ways to have fun and keep from being distracted by the obvious buzz kills. My passion/focus is motorcycles and I'm more than good with that. ENJOY the project and personalize it to your own aesthetic vision. Good stuff right there.
 

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and my daily ride is a 2008 Suzuki C90T which is unmolested except for Mustang seat and 4 inch handle bar risers. Will post results soon. Thanks again!
Good for you.

This is an ENTIRELY different situation than those who tear apart their only ride and then cry when it doesn't run right anymore.
 

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Discussion Starter #17
Ok, got the proper mixture screw. Of this I'm certain. The original had like a two step tip. Anyway, it still just tries to fire upon starting with black smoke from the exhaust. I only have the mixture screw turned out 1 1/2 turns. Factory spec is 3. All stock jets are back in the carb. Not getting enough air flow through filter? And opening the throttle still kills it.
 

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with black smoke from the exhaust.
Mixture WAY too rich.
Try it with the air filter OFF and see what happens.
Could be float too high, allowing too much fuel into the bowl.
Could be a gasket leak or a crack in carb body allowing raw fuel into the throat.

I think I even remember hearing about a failed diaphragm in an "automatic" petcock allowing gas directly into the manifold.
 

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Discussion Starter #19
Mixture WAY too rich.
Try it with the air filter OFF and see what happens.
Could be float too high, allowing too much fuel into the bowl.
Could be a gasket leak or a crack in carb body allowing raw fuel into the throat.

I think I even remember hearing about a failed diaphragm in an "automatic" petcock allowing gas directly into the manifold.
thanks. that's what I'm thinking. weather here has not allowed me to tinker much except in the garage, so taking it out to start has been limited. i'll check the air filter first of course and let you know what I find. I do know float height is correct.
 
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