ZS250 GS cutting out strangely

[darealestspigguh]

Well my bike is starting (only with choke) and running strong without choke.  However i run into a problem when i first start to ride the bike.  It will run indefinately while at low to middle revs and through all five gears . But heres whats confusing when i hit higher revs it will get there and stay there, but comming off the throttle it will not go back to idle, it just cuts out.  If i still have speed i can clutch it back on... sometimes, but most of the time i have no luck.  Last night i ended up pushing it a couple blocks back to my house because the battery died trying to restart it after it cutout.  Could this be caused by improper float adjustment causing the bowls to empty as opposed to filling constantly while at high revs? If this were the case, why doesn't it cut out while im still revving? This right now is my only theory so i think i'm gonna pull the carb today or tommorow. Also, it seemed last time i rode (previously to last night's fiasco) that once i got it going, it stopped having this problem all together, it did do it a few times while the engine was still warming up.  I also might pull the plug, see if im fouling the shiny new iridium  

[leemoore01]

Where did you get the adjustments for the carb and what is the process for adjusting

[darealestspigguh]

various places, but i kinda just winged it with the float, move it a little, then try it in the engine until you get it just right. It wasnt working well at factory 15mm since i added K&N filter and removed EGR.  I got it to run a little leaner now by moving the needle clip to the top position since it was fouling the 8 plugs which are also factory spec when i ran it at open throttle for 5 minutes (needle adjustment).  I just got a 7 which is one heat range lower and once the 8 iridium that i have in there fouls out i'll throw it in to see if i can get better ignition without causing detonation.  She runs good now, though not as strong as with the rich mix.  I posted another topic about a third jet hole in the carb with a rubber stopper in it.  Since i'm still only reving to about 9000, i am guessing this is where the main jet should go so as to get better power at WOT.  If anyone can confirm or deny, that would be great, cause im just conjecturing.  i really feel like drilling that sucker out and putting a jet in ther to see what happens, but i'll wait for the facts.

Where did you get the adjustments for the carb and what is the process for adjusting

process for adjusting starts with making sure you have a regular spark and an engine that will turn over.  Once you have the engine running, i would start by using a new plug in it for a good 50 miles.  Then you can pull the plug and it will tell you how your engine is running (lean or rich) and at which throttle position it becomes rich or lean.  From there it is as simple as movinng the jets in or out or moving the needle up or down.  Float adjustments are usually not necesary but if you think it is causing your problem, use a vernier caliper to check that it is at factory spec:15mm.
If you have never done any of this and it sounds confusing, dont fret.  Neither had i before i got this bike, just check youtube and other sites for free tutorials (videos are best) and you'll be able to figure it out, so long as you can use a screwdriver...

[darealestspigguh]

No more cutting out at high engine speeds, at least not while it's warm.  I took the carb off yet again and adjusted the float very slightly.. I also turned the main jet 1 and a half turns out, it was all the way in before and it would cause the lean condition at high revs.  So now i am at the top clip for the needle, idle screw about three turns out and main jet 1 and a half turns out.  This setup seems to be the sweet spot with my K&N filter and debaffled exhaust.

[darealestspigguh]

ok so last night's adjustment didnt flood the engine like previous adjustments have, but it seems when the engine is cold, it may be a litte lean or rich at the lower rpm's, there is some hesitation when i give it small amounts of throttle such as when taking off in first in a parking lot.  Heavy throttle is great though, second is going even a little past 9000 now with no sputters but the little 230 sounds like it's gonna pop.  I'm, going to try some idle screw adjustments to see if that helps.

[darealestspigguh]

Well i moved the needle clip down one so it's now at the second from the top.  The top seemed fine until i tried to get some real speed with quick shifts, it started popping and hesitating in 4th and 5th, so much so, it tried to cut out in fifth.  However, if you're not racing around town, and you can keep it under 6-7000 the top should be fine.   

[z250gs]

No more cutting out at high engine speeds, at least not while it's warm.  I took the carb off yet again and adjusted the float very slightly.. I also turned the main jet 1 and a half turns out, it was all the way in before and it would cause the lean condition at high revs.  So now i am at the top clip for the needle, idle screw about three turns out and main jet 1 and a half turns out.  This setup seems to be the sweet spot with my K&N filter and debaffled exhaust.

Seems like your having a few probs since the new setup. I don't see what exactly you mean here by "main jet was fully in and is now out 1.5 turns". From memory when i pulled the carb apart, there is a main jet that is affected by the slide position, which in the case of these CV type carbs has a needle operated from the venturi air pressure. The throttle doesnt act on the needle directly like with normal slide carbs. The main jet is screwed down fully and is not to be unscrewed otherwise it will vibrate its way out and cause big problems. Next to the main jet is a pilot jet-also firmly screwed in. These two jets can only be replaced. You mustnt unscrew them and leave them loose.

 On the outside of the carb is a small spring loaded idle speed adjustment screw, that should be turned out about 2 turns from the "fully in" position and adjusted for the low speed running. It won't affect the high speed running.  

With your new setup the normal condition due to the unrestricted air flow filter and exhaust pipe would probably mean the mixture is now leaned up. Moving the clip UP is making it more lean.
    
I would have thought you would maybe need to alter the clip position a notch or so in the Down direction, but probably will need to richen up the mix by rejetting (the main jet) for a slightly bigger, maybe 1 size up only to get the right high speed running.

By the way, when you pulled the carb out did you check the diaphragm is installed ok with no gaps around the edges and no perforations? Apparently that can be a source of problems in the medium and high speed setup.

P.S. yeah your bike looks neat in black from your pic there. I notice in US they only sell one color-silver.
Down in Asia they paint them in Silver, Blue or Red but that black color u did looks ok from the distance. Is the finish nice and smooth or did u get runs in the paint?

[darealestspigguh]

No more cutting out at high engine speeds, at least not while it's warm.  I took the carb off yet again and adjusted the float very slightly.. I also turned the main jet 1 and a half turns out, it was all the way in before and it would cause the lean condition at high revs.  So now i am at the top clip for the needle, idle screw about three turns out and main jet 1 and a half turns out.  This setup seems to be the sweet spot with my K&N filter and debaffled exhaust.

Seems like your having a few probs since the new setup. I don't see what exactly you mean here by "main jet was fully in and is now out 1.5 turns". From memory when i pulled the carb apart, there is a main jet that is affected by the slide position, which in the case of these CV type carbs has a needle operated from the venturi air pressure. The throttle doesnt act on the needle directly like with normal slide carbs. The main jet is screwed down fully and is not to be unscrewed otherwise it will vibrate its way out and cause big problems. Next to the main jet is a pilot jet-also firmly screwed in. These two jets can only be replaced. You mustnt unscrew them and leave them loose.

 On the outside of the carb is a small spring loaded idle mixture screw, that should be turned out about 2 turns from the "fully in" position and adjusted for the low speed running. It won't affect the high speed running.  

With your new setup the normal condition due to the unrestricted air flow filter and exhaust pipe would probably mean the mixture is now leaned up. Moving the clip UP is making it more lean.
    
I would have thought you would maybe need to alter the clip position a notch or so in the Down direction, but probably will need to richen up the mix by rejetting (the main jet) for a slightly bigger, maybe 1 size up only to get the right high speed running.

By the way, when you pulled the carb out did you check the diaphragm is installed ok with no gaps around the edges and no perforations? Apparently that can be a source of problems in the medium and high speed setup.

P.S. yeah your bike looks neat in black from your pic there. I notice in US they only sell one color-silver.
Down in Asia they paint them in Silver, Blue or Red but that black color u did looks ok from the distance. Is the finish nice and smooth or did u get runs in the paint?

The paint looks good from far like you said, but when you inspect closely you can easily see where Miaimi left it's humid little marks under my paint (i.e.cracks and fisheyes).  I understand what you are saying about jetting, and i have corrected any mistakes, but i don't see how a jet kit would stop my floatbowl from emptying so quick, it seems the only way to fix that is to get a bigger carb, meaning a bigger floatbowl it seems a bigger jet or two bigger jets would worsen my problem.  My diaphragm is one thing i make sure is done right every time i install my carb. However you mentioned the idle screw should not affect high speed operation, however it  seems to change how quickly my revs drop back down to idle from giving full throttle.  How do i accurately adjust for quicker return to idle?  Also if i wanted to rejet myself, i would need to pull the current jets to compare right?

[z250gs]

My bike is completely stock, so anything i say here is only guessing .

What makes u think the float bowl is emptying too quick? I can't see how the increased airflow you've created could alter the air/fuel ratio that much that you could drain the bowl. The needle and seat setup in the float bowl will easily compensate for the extra fuel you might be using after altering the needle clip height. If the fuel is too low then you may have a partly blocked fuel line or clogged screen in the fuel tank. Maybe check that.

If the carb is getting the fuel ok then what i think may be happening is as the engine comes rapidly off high revs, the mix goes briefly too lean, stalling the engine because the low speed carb circuit (pilot jet inside the float bowl) is too small for the increased air flow at low revs.  

I think you need to read the plug color, as you mentioned you were doing, to find out what the high speed circuit is doing (rich or lean or ok). Then the same for the low speed circuit. Drive at high revs for 5 mins, hit the kill switch and pull in the clutch. Pull over and check the plug. From your earlier post it sounds like the fuel is lean, popping and stuttering, You'd expect that after your K&N filter and new pipe. Then drive around for 5 mins at low speed, say less than 3000rpm and stop engine and check plug color.

Another quik test is :When the engine stalls after being warmed up fully does it restart better by pulling the choke on a bit? If so it sounds like it is lean at low speeds so the rejet of the pilot may be the way to go. Also, can you start the engine from dead cold without the choke? That could indicate the low speed circuit is too rich.

If you need to get new jets they should only cost a few dollars each, but where you  get them from I don't know.  May be best to check with a carb or bike shop there. Our bikes use TK (Teikei) carbs (type=MV30P-1J on mine) that are similar to the carb used on the Yamaha TW200 bikes - but they use a TK MV28 carb. So Yamaha dealers may be a source for parts. There is a US (Ohio?) website, http://www.endlessjourneycycles.net/  has a few posts about rejetting and general carby stuff. It may be worth ringing this guy for advice based on experience. Otherwise you may just spend a lot of cash and time and end up with a badly running bike.

Re the jet size, should be stamped on the jets, hopefully. May need a magnifying glass. I think someone put a post on this site about the jets but i can't find it.

[darealestspigguh]

My bike is completely stock, so anything i say here is only guessing .

What makes u think the float bowl is emptying too quick? I can't see how the increased airflow you've created could alter the air/fuel ratio that much that you could drain the bowl. The needle and seat setup in the float bowl will easily compensate for the extra fuel you might be using after altering the needle clip height. If the fuel is too low then you may have a partly blocked fuel line or clogged screen in the fuel tank. Maybe check that.

If the carb is getting the fuel ok then what i think may be happening is as the engine comes rapidly off high revs, the mix goes briefly too lean, stalling the engine because the low speed carb circuit (pilot jet inside the float bowl) is too small for the increased air flow at low revs.  

I think you need to read the plug color, as you mentioned you were doing, to find out what the high speed circuit is doing (rich or lean or ok). Then the same for the low speed circuit. Drive at high revs for 5 mins, hit the kill switch and pull in the clutch. Pull over and check the plug. From your earlier post it sounds like the fuel is lean, popping and stuttering, You'd expect that after your K&N filter and new pipe. Then drive around for 5 mins at low speed, say less than 3000rpm and stop engine and check plug color.

Another quik test is :When the engine stalls after being warmed up fully does it restart better by pulling the choke on a bit? If so it sounds like it is lean at low speeds so the rejet of the pilot may be the way to go. Also, can you start the engine from dead cold without the choke? That could indicate the low speed circuit is too rich.

If you need to get new jets they should only cost a few dollars each, but where you  get them from I don't know.  May be best to check with a carb or bike shop there. Our bikes use TK (Teikei) carbs (type=MV30P-1J on mine) that are similar to the carb used on the Yamaha TW200 bikes - but they use a TK MV28 carb. So Yamaha dealers may be a source for parts. There is a US (Ohio?) website, http://www.endlessjourneycycles.net/  has a few posts about rejetting and general carby stuff. It may be worth ringing this guy for advice based on experience. Otherwise you may just spend a lot of cash and time and end up with a badly running bike.

Re the jet size, should be stamped on the jets, hopefully. May need a magnifying glass. I think someone put a post on this site about the jets but i can't find it.

Wow, so much helpful information and in such quick time, thank you.  I believe you're right on the money about the stalling when it's lean after high revs, but does that mean i need a new jet or just to adjust the idle screw to be more rich?  

It does not seem to be too rich, probably lean as you said since with my current setup i often have to start it by popping the clutch in second with choke, however it idles fine and starts right up when warm.  Also you said if the low speed circuit were rich, it would be easier to start cold correct? if the bike stalls out after ridig at WOT and i try to clutch it back on, i can hear the engine turn over but then cough and die even when i give it throttle, thats why i was thinking empty float bowl.  

Also, i read that some jet kits include a drill bit for drilling out plastic plugs, i noticed a circuit plugged this way on the bottom end of the carb, is there any reason i should drill this out? 

I am going to pull my jets and take them to a yamaha dealer called Broward oto see if they can find jets for me. I'd prefer to order something like that in person... Thanks again for all of your help.

[z250gs]

How did u go there-did u get anywhere with the plug reading? I think u need to confirm the high speed cct is running rich or lean before doing anything else. If it is lean you might hear it popping from the exhaust as you backoff the throttle running down hill for example. Somewhere above 3/4 throttle to WOT the needle is fully out of the MAinjet so this is the high speed cct range to test in.

As for the idle adjust, yeah i think the idle fuel screw is factory plugged. As you say, you may need to remove the plug.

And yes again to   "if the low speed circuit were rich, it would be easier to start cold correct?" But what i mean is it will start without the choke being used when the engine is dead cold. That will mean that the fuel supply at idle is rich already so no choke required to cold start. I reckon you WILL need choke at cold start with your mods 'cause its probably running lean in the 0-1/4 throttle range ie the low speed cct.

If your generally running lean, with popping and backfiring youll probably wreck the engine soon if you keep riding it for extended periods. It's better to run it on the rich side rather than lean. Did you move the clip DOWN a notch or two. The stock position is slot 3 ie right in the middle slot. Slot One here is the top, wide end of the needle. Try slot 4 or 5. Lets see what happens there.

[darealestspigguh]

The reason i moved it up in the first place is cuz it was flooding when i crank without even using choke, but that was before i adjusted the floatbowl so i'll give it a shot.

i'm also reading about mods in which you drill a second hole in the slide to increase throttle response.  Also a spring cutting mod, to the same effect.  Would you recomend any such upgrade.  I also sent a message to sigma 6 on ebay who offers a jet kit for our bikes. It includes instructions for both of those mods as well as new jets. They say they will allow me to test them and send em back for different ones if they dont run right.  So i'm thinking about paying the $58.00, not that i have it to spend right now...  

It's deffinately lean though, i can feel it in the higher gears much more for some reason.  It runs through first second and third strong, but once i hit 5th it's starved, and if i give it WOT, it ends up stalling when i let it go.  So first thing in the morning, i'll move it back to the 3rd position, and then go down from there.  What is a tell tale sign that i'm way too rich? backfires right?

[z250gs]

Too high a fuel level in the float chamber will cause rich mixture/flooding.

I just had a look at that 6sigma racing mod kit. Sounds like the way to go. They've got kits for just about every bike on the street there- but most importantly, one for the zong! If they live up to their claims they provide a complete carb kit with everything you need and after sales advice, phone help etc and full instructions with a money back guarantee. For $60 it may be better to order their kit rather than looking around for individual parts from a whole lot of different sources. I notice they ask you to provide details of the mods youve done so they can tailor the kit to your bike exactly. Definitely better than trial and error doing one thing at a time. Could save a lot of time.

As for running rich, this might work: Run the engine with some load , like uphill within the 1/2 to WOT range and watch for any hesitation or stumbling or bogging. When you find poor running, pull off the road and pull the spark plug out and check the plug for fouling on the center electrode. That insulator may be white if its running lean at that point. But if its rich it will be sooty or carbon fouled. Thats how i'd try to test for rich running. THe plug should tell you. By the way, dont forget to pull the plug before starting the test run. Make sure its nice and clean and gapped to 0.6-0.7mm or whatever your manual says.

Those other mods you mention like cutting the diaphragm spring and drilling holes in the slide etc,,--Ive not heard of those mod. Put it this way, sigma seem to know whats required for our carb and bikes taking into account the mods you've made, whereas the info about drilling holes in the slide etc is probably not a solution specifically for our Teikei CV carb. So i say go with the kit.

      

[darealestspigguh]

hey guys, sorry for the hiatus.  I have finally recieved and tried to install my sigma 6 jet kit.  Right out of the envelope, i thought there might be a problem.  They sent three jets 130, 135 and 140, nither of which fit any of my carb's jets holes.  The jets they sent did not even resemble the currently installed ones.  The only mod that came with the kit that i have been able to perform so far is the drilling out of the jet that was plugged.  It seemed to increse fuel flow through the entire range as i had to lean out all my settings to get the engine running smoothly again.  I am now running with the clip on the second notch from the top with no shim and idle screw about two turns out.  The bike runs well with none of the quirks it used to have, but it still seems a little lean to me.  I will maybe add the shim back to see if i like it there.  Otherwise, the jet "kit" has proved to be useless as i planned to drill the stop out anyway.. Theres also intructions for drilling out a second hole in the slide for increased throttle response. However, the instructions state that this could adversely affect low range rpms.  Sounds like that might make my bike bog more often... fuck that! well i contacted sigma already with this tirade so hopefully i will get some more support, possible some propper jets.

[darealestspigguh]

if anyone has any spare jets for the 250 gs i need pics to send to sigma6 for matching and i dont want to pull my carb apart since i just got it running decent.  Anyone? anyone?