04-04-2009, 11:32 PM #1
STX15f Idle problem and pulsing on light throttle
Hey guys, sorry about the long winded post but I need some help here...
- I bought a '06 15f with 60 hours on it. I have done about 5 hours and now I have just noticed it is idling rough (goes form 1000rpm to 1300 and back to 1000rpm) and at certain revs on light throttle it will pulse (I dont know if this is a good explanation, it kind of stutters a little - its not huge but its just noticable at low speed) and then when I give it some slight throttle it sometimes hesitates for a half second before it gets going - it kind of feels like its mildly cavitating and the back of ths ski gets a slight vibration. At full throttle its fine though... but at full throttle from any speed there is no hesitation at all...
At first I thought it might be a chipped prop or bent shaft but the rough idle is there when its on the trailer and out of the water also. I have cleaned the plugs thoroughly (I am waiting for new plugs to arrive- so I just cleaned the ones I had and put em back in).
I'm in regional australia so it takes a while to get parts and if I want to take it to a mechanic its a 600 mile drive each way... so I am hoping someone can help me and tell me what I should be checking next? everything I have checked so far seems fine (water flow out the p*sser is fine, oil is beautiful and clear, everything is dry inside the engine compartment - I even let it sit out for a day without the cover to make sure everything was extra dry...).
I have a service manual (for the 05 but I understand there is not much different-is this true?).
And if I cant find anything wrong is it ok to ride it like this or should I get it to a dealer for a full check up - I mean really its not that noticable at all, Im just really picky and carefull with my stuff - lest I cause more damage... so Im wondering if I should ignore it and just ride it.
One other thing Im curious about is it lways ends up with about a cup to two cups of water in the channels under the back seat section after each ride -I ride it pretty hard and the nose gets fully under the water occasionally when I am doing turns and stuff- so is this water normal? (I have never owned a ski before- Ive got bikes but never had a ski)
As I said at the start sorry about the long winded post but I am really scratchin my head and worried if I should or shouldnt ride it and there is no-one I can ask within 600 miles....
Thanks in advance for any help
04-05-2009, 12:28 AM #2
I forgot to mention when I pulled the plugs number one was the only one that looked like it could be fowled... I just took the ski out again and it is definately idling like a pig and when I hold the throttle around 3000rpm it will fluctuate up or down 250-500 rpm . Its intermittent - it will hold the revs for a while then it will jump and fall-then it will hold again on and off. It will still do top speed every shot though and seems fine under full throttle (even for a lengthy period under full throttle it doesnt fluctuate or stutter)...but if I give it full throttle when it is fluctating/ stuttering it will hesitate for a second and then go..
Any ideas anyone? Could this be fouled injector/s or plugs (Although I cleaned the plugs could one still be dicky and replacing it might fix them?)...
when I got it home and flushed it the revs were jumping from 1000rpm to 1250rpm and back down to 900rpm - basically just fluctating and idling rough....
Am I right in thinking this is a motor issue and not a driveshaft / impeller/prop issue as it does it when sitting on the trailer and out of the water?
I know I'm new to this but any help is greatly appreciated as I am miles from any service centre and would like to sort this out myself if possible...
04-05-2009, 03:46 AM #3
jihwaan Welcome to the Forums!
I think a little fluctuate is normal. Yours might be too much I dont know.
My number one plug is also always the worst. Replace the plugs when you get them and hopefully it will idle better and not hessitate when giving trottle.
Sometimes when I start my ski it is realy rough, like it fires on three cylinders or something, when I give it gas it hessitates, once it gets going though it runs fine.
The water in the hull is perfectly normal. It gets sucked out through the blidge system when your ski is running.
Your service manual is the correct one!
04-05-2009, 04:22 AM #4
Thanks heaps for the info, Im a little less worried now...
I just figured being fuel injected it should be a bit smoother than it is... the fluctuation in the revs is what puzzles me. Its weird, it will run good and then start running rough and then run good again... but it isnt overly noticable in most cases.. although the idle is rough as guts and when it drops to 900rpm I keep thinking its gonna stall one me...
04-05-2009, 07:48 AM #5
04-05-2009, 08:37 AM #6
checking the valves is a huge job isnt it?
oh well if its gotta be done I suppose, but ill keep my fingers crossed the plugs fix it.
Funny thing is I have friends with zx14 ninja road bikes (basically same motor) and they had their valves checked at 20,000 miles and they were perfect... so it would surprise me if it was valves, also the fact that it comes and goes makes me think it aint valves as if it was valves wouldnt it be constant? Im out of my depth here so correct me if I am wrong...
Im actually beginning to think maybe dirty injectors, or maybe just a bad batch of fuel? Im gonna empty this tank when my new plugs arrive and see if that helps, and maybe get the injectors cleaned (ultrasonic cleaning)...
If it was the valves would there be any other symptoms?
04-05-2009, 09:50 AM #7
Sounds like a plug issue Ive had and am still having with my 250x.Rough idle when i first start it, for the first five minutes i ride it, it has a rough idle, only reaching 50mph, but after a good 10 mins of random throttle use it seems to warm up and burn up whatever is on the plugs(iam guessing).Plug change of the effected plug solves the rough idle. Best way to check if plugs are bad is when its running just remove each plug wire, one at a time to pin point which plug it is. The plug wire you remove which doesn't change your rough idle will tell u which plug is bad.
We have a channel here in Havasu which takes 30mins to idle through which can cause my plugs to foul. Also, what i here is there is denso iridium plugs for the 250x that are less likely to foul, and there cheaper, not positive if there for 15f,
same engine right? so i dont see why they wouldnt.
I bought an extra set before i heard about Denso's so i havent tryed them yet but theres plenty of talk about them on GH.
04-05-2009, 10:22 AM #8
- Join Date
- Mar 2008
You might want to check your fuel.. bad fuel can make one idle rough. There is some stuff out there called sea foam, get a can of that and put it in the tank and top off the fuel and see if that will help. doing a plug swap would do alot for it as well. Welcome to the forums, I wouldn't think there is a valve problem there .. this sounds more fuel related than anything else. Just make sure you use the higher grade of fuel in it. In the U.S. its 93 octaine.. not sure about it down under. .. good luck to ya
04-05-2009, 10:23 AM #9
Hey guys I have to say thanks for all the help so far and the greetings. I think this forum will be getting a fair bit of my attention... Im at a loss with this and all the suggestions and advice are appreciated greatly!!
I'm hoping its the plugs. Does yours stutter and/or kinda hesitate for a second or two when at certain low throttle loads also (but totally randomly)?
Mine doesnt seem to get any better after running for a while, if anything it gets a little worse I think... I am yet to pull the plugs after todays run so it should be interesting to see if number one is fouled again...
Number one had a slight amount of rust around the last thread (which sits in the cylinder when its screwed in - funny that- Makes me wonder what the inside of no.1 cylinder looks like then hey..) and was *slightly* fouled by my standards ..but all other plugs looked good
My only other thought is coil packs - one might be dicky?.. or maybe the idle control is playing silly buggers? doesnt this ski have some thing that increases rpm when turning or something...(I read that somewhere) I presume it would use an idle air bypass valve for that... anyone know if this is the case and if that could be playing games with me also
Can anyone tell me how I can test the coil packs? should I just buy an extra coil pack and swap them one at a time and see if that helps (if after I swap plugs it doesnt help) coz I figure if its spark related and its not the plugs the next culprite might be the coil pack/s?
thanks in advance everyone...!!!
04-05-2009, 05:46 PM #10
When you turn on your key or start your motor, does the display flash any codes? If it was coil or fuel injectors, it would show some code on display. Not sure which ones. But you have the manual so check there. Or check back here if you are showing any codes. You can also hook up the fuel rail to pressure gauge to see how much pressure your getting there. And last but not least, does the area where you live sell ethanol blended gas? Could have some moister build up in gas tank or fuel system. Freinds 12F had same problem and took out tank, fuel pump and cleaned real well and she fired right up and ran perfect. Again, check for codes first.
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