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Discussion Starter #1
Hey every one, I got a Z and since i got it back from my dealer about last year been having a rev-idle prob. after been riding or hot ill rev it up in neutral and let off quick and it stays rev-ed high for a second or two then back to normal idle, thinking i have a jetting prob the shop didn't do right or something else, appreciate the help....
 

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You are experiencing a "hanging idle" If it has done it since you got it back, then yes, they did it wrong, probably because they tried to set it at the factory spec, instead of where it works good.
What happened, is that they set the fuel screw too lean, which makes the idle weak. Then they had to speed the idle up to compensate. What you end up with is a unstable idle with the throttle blade open too far causing the hanging idle...


Long story short, what you need to do is open the fuel screw 1 turn, and slow down your idle speed to normal after that. As soon as you open the fuel screw up some, (richening it back up to where it runs decent), the idle speed is likely to go high. Then you set the idle speed back to normal and your good to go.
 

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Discussion Starter #3
thanks CFM , ya they did my jetting on it and put the Yoshi pipe on and even forgot to put a exhaust clamp on it , got a uni ilter on too. That problem explain the popping I'm getting after i let off on the throttle. By the way they went out of business :)
 

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I haven't messed with a 250, pretty much where it sounds normal. Yes, being lean on the fuel screw will also cause a backfire when you let off.

If you find you are beyond 3 turns out, and are still having those problems, then either your pilot is too small, or is partially plugged. Usually any 4 stroke with a stock pilot needs to be right at about the limit (3 turns out) You might have better results with one size bigger pilot jet, and less turns out of the fuel screw.
 

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Discussion Starter #6
Thx man ill check all that out and and more unlikely have to adjust the fuel screw and probably give it a cleaning, it will be my first time taking the carb apart , is their a site were i can get a schematic for a 2006 ltz250. and the do's and donts.
 

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First I would try adjusting the fuel screw. Im not familliar with that carb, but it should be in front of the fuel bowl, sticking straight down. There may be a plug blocking access to it. (Your tax dollars wasted by our lovely EPA)

Your best bet is probably to loosen the clamps and tilt the carb so you can see good.

If there is a plug blocking access of the fuel screw, you can drill it, thread a wood screw into it, and pull it out, so you can get to the fuel screw. I would take it right to 3 turns out, because the stock pilot is usually borderline small.

The EPA doesn't want us tuning our own carbs for some reason, which is rediculous, because they get dirty and out of adjustment, and end up making worse emissions unless we can get in there and fix the problem. The bottom line is the EPA is not as smart as they think they are... Thank god they are in charge of making it more difficult to keep our machines running properly :rolleyes:
 

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Discussion Starter #8
sounds good ill give it a look see , my buddy is having a carb issue 2 , its leaking gas out of the over flow tube so ill take it over their and give a good looking over thx CFM, ill let you know how it turns out.
 

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FYI

Both my stock z carbs leaked from the overflow tube at one time or another and the fix for both was a new 0-ring on the needle valve.
 

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I have a z250 and it does the same thing. I guess I neglect it. I never got around to fixing it. I know it's running lean on the idle circuit. Nothing a couple jet sizes up won't fix. I'm at the end of my adjustment on my idle mixture screw. To the op, I'd change the pilot jet by 5 sizes higher. That should give you your adjustment range on your mixture screw.
 

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Keep in mind that everything leaks from the overflow tube when you shake it. If it leaks sitting still, that is a problem. Usually needs a needle valve, or like mentioned, an o-ring if it uses one to seal the seat to the carb body.

And I have never seen any powersports engine respond favorably to more than 1 size pilot change. You will get a rich stumble up to 1/8th throttle. Not a huge, deal, but not "tuned" either. You are better off taking it 1 step at a time with pilots.
 

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Discussion Starter #12
Thx guys, ya my buddies has to turn off his gas 400ex and run it till it eats the gas in the bowl then turns it off and then he has no leak but if he stops turns it off it leaks pretty much every time. but ill try and go up one pilot jet and 3 out on fuel screw.
 

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I've been looking for this answer for months myself. I also need to rebuild my carb on my sons 04 ltz250. Should i stay oem or upgrade? I am looking to get more throttle response and dont know where to start.

If anyone is wondering I also took my fuel pett WooterWooterWooterWooter off and put the same year yamaha raptor fuel WooterWooterWooterWooter on. Plugged my vaccum hose with a bolt and tied it up to frame. This gave me a off position and bolted up perfectly.

If anyone has info or a thread taht talks about beginnig mods for ltz let me know.
Thanks guys.
 

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Discussion Starter #14
rev issue

ya their is a mod I heard about that im not gonna do my self is take a ltz400 carb and put iton a 250, Man im 325 pound dude and i have z250 2006 and only have a slip on yoshi jett kit and a dual stage UNI filter with ITP trac stars all around and aftermarket handle bars and this bike I can say is a trooper and gonna get a hot cam in it when i rebuild it . Its been a real tuff bike even with my fat A** on it:p. besides a port polish and new piston with higher commpresion ratio, and titanium valves and all the goodies its not worth it get a bigger bike , this company frogot the name of it sorry , told me send him my motor and carb he will put a bigger iston in it valves , a cam they make for it and port and polish and their jetting witch i think they put a z400 carb in it and gonna cost me between $1,400 and $1,600 for all that when i can pay $3,000 for a 400 or $3,800 for a older 450R. so dont spend alot of time upgrading the 250 just do the basics and put some wheel spacers on it and it will do you right.;)
 

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Discussion Starter #15
Hey cfm , I got it going good for a real short time then started to back fire on deceal and going down hills with no throttle, put a shindy carb kit in it and a 138 main jet with a stock 20 pilot jet and my plug is white with about several rides on it its a dr7ea which is the hot plug gonna put the 8 back in it, but it had a real light spot of tan on it. stock jet sizes are 125 main and 3rd clip and needle and 20 pilot jet
my altitude is a little above 3000 feet like 3100. and their where flames or some thing what look like fire when it back fired when rev to limiter, and been threw like tons of posts and links about lean and rich. just trying to get a full understanding about carb adjustments to get a head start on getting in to MMI here in phx,az. been learning alot since last post and rebuilt my 1990 dodge Plymouth sundance motor runs great with new crank. People say back fires on deceal means gas is burning in header and lean backfires on acceleration and my plug should look tan to dark brown and some say that it don't matter. that's another reason for going to MMI besides a career.Gonna adjust my valves Saturday hopefully , my friend is gonna help me do it so next time I can do it my self.
 

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Hey cfm , I got it going good for a real short time then started to back fire on deceal and going down hills with no throttle, put a shindy carb kit in it and a 138 main jet with a stock 20 pilot jet and my plug is white with about several rides on it its a dr7ea which is the hot plug gonna put the 8 back in it, but it had a real light spot of tan on it. stock jet sizes are 125 main and 3rd clip and needle and 20 pilot jet
my altitude is a little above 3000 feet like 3100. and their where flames or some thing what look like fire when it back fired when rev to limiter, and been threw like tons of posts and links about lean and rich. just trying to get a full understanding about carb adjustments to get a head start on getting in to MMI here in phx,az. been learning alot since last post and rebuilt my 1990 dodge Plymouth sundance motor runs great with new crank. People say back fires on deceal means gas is burning in header and lean backfires on acceleration and my plug should look tan to dark brown and some say that it don't matter. that's another reason for going to MMI besides a career.Gonna adjust my valves Saturday hopefully , my friend is gonna help me do it so next time I can do it my self.

Popping on decell can be either a lean condition between either the fuel screw, pilot jet, or an intake leak, OR it can also be caused by an exhaust leak. Check your exhaust for leaks, I bet something is coming loose.

Forget trying to read the spark plug, it will mislead you. If you really want to read the plug, you would have to kill it at wide open, and cut the threads off to see what you need to see anyhow. Throw that hot plug away too. That's a good way to detonate the thing. Did you get rid of the hanging idle?
 

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Discussion Starter #17
Looked for leaks and the exhuast had one since back from the dealers like 4 years ago they frogot the clamp for it so put another one on it with some copper gasket sealnt for it, looks good now,well two months now the head gasket look good too so does the intake, hanging idle is gone , dirty carb, cleaned it and was good to go for a week and a half then all this back firing is going on trying to see if i should get a bigger pilot jet tommarow or wait till the valves are adjusted to where i know that their good cause the shop i took it to did the vavles to so im scared to look at em,lol. they had a 116 for my main jet when they did it, and i beleive they messed up big lower u go the higher the altitude , higher the number the lower altitude. so they messed up right im at 3100 feet stock size is 125 have a 138 now with a 20 pilot.whats the next pilot i should go up?or what do you think i should do first like a trouble shooter guide.
 

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The higher you go in elevation, the leaner you need to set it up. At 3000' you only need to lean it a size or so from what is recommended. That shouldn't be messing up your pilot any either. Some debris might have gotten in the pilot or something.

Exhaust leaks can be tricky to find. I've never tried it, but a candle or lighter next to an exhaust joint while you hit the gas should show you an exhaust leak that you might not otherwise find. Just don't catch anything on fire.
 

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Discussion Starter #19
just cleaned it this last weekend but 138 from 125 to much then cause i heard dyno does their jetting numbers differently from other manufactures like a 125 mukuni is equivalent to a 130 dyno-jet kit. Im gonna do a water bottle test around the intake again and the flame for the exhaust . ill try that. and get the spark plug here later today. go back to the dr8ea.Ill keep ya informed man let ya know what comes out of this learning experience,lol.
 

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Yeah, dynojet and mikuni are on different scales. There's a chart posted somewhere around here comparing them. I think we stickied a topic about it.

Good luck, don't worry, it gets easier.
 
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