Another Stutterer

[Soapy]

I've just joined the Forum and as I stated in the Introduction Forum I found this site when I Google searched with my symptoms. My FZS 600 is a 2003 only 3500 miles on the clock and I've owned it for 2 years. It has a K+N filter and has a Beowolf Can with baffle in. It was fine last year. Because of work and weather I put it into the shed last October.
Brought it out last month and put her through an MOT. Now this is where the fun starts, NOT!!!
When I first ride it there doesn't seem to be a big issue. But after riding for a couple of miles if I quickly open the throttle the bike judders like a misfire and will judder continuously through the rev range. Whilst it is juddering if I back off the throttle slightly and then open it up slowly it will more often than not be okay. But as soon as I try and do a quick increase it bogs down.
I experimented and found from a standing start if I gently eased the throttle up through the revs and gears it will operate as far as I can tell normally all the way to full throttle and redline (and illegal speeds). Also sitting in Neutral after the stuttering has started if I whang on the throttle there is a stutter at the start before it picks up. But same again if I open the throttle slowly it appears to rev ok.
After trawling through the forum and seeing what other people have done here is a list of what I've tried with no success so far :-
 
Replaced Plugs
Cut back 1/2" on Coil Leads and refitted Plug Caps (Screw and coil cable copper look good),
Removed tank and emptied old fuel out. Looked inside an tank base is clean as a whistle.
Removed Fuel Tap and checked filter.
Inspected K+N Filter
Visually checked fuel filter
Removed Carbs and removed Main Jets and the Metal Tube underneath it, Needle Jet? or Emulsion Tube?
Removed the other jet beside it. Pilot Jet?
All where clean with no signs of any contamination.
Inspected Inlet and Air Filter Box Rubbers. No obvious sign of cracks or perishing.
Reassembled everything and put a fresh couple of gallons of fuel in the tank.
Started pretty quickly but a few minutes into a test ride and the symptoms are back.
I haven't taken the top of the carbs off and checked the Diaphrams because I don't know what to check or what I'm looking for.
Would a dodgy fuel filter cause these issues. I have discounted this for the moment because I thought the fuel in the float bowls would initially keep the engine going and then it might fade later if the fuel filter couldn't keep up with demand.
Pump sounds ok when ignition switched on, it pulses away and seems to hold fuel pressure.
I'm getting to the limit of my Mechanical skills and am running out of ideas.
I was thinking of trying it with the baffle out to see if it makes any difference or buying an original paper air filter and refitting the original can.
But I think I'm clutching at straws because it ran fine with this set up last year.
Apologies for rambling on.
Any input extremely welcome.
Cheers
John S

 
 
 
 

[Chris]

Hey,
 
Sorry to hear of your troubles. I'm not sure what else there would be to check which might cause the problem you're having but I am in Shetland so if you need a hand with anything then let me know.
 
Chris

[red98]

hi john....welcome to the stuttering ccccccccclub,well you`ve covered most things....you did`nt mention float needle jet in the bottom of the carbs ,controls the flow of fuel to the float bowls,also worth checking the diaphrams,look for splits and make sure they are nice and flexible and that the needle is a nice smooth action....same symptons as my stutter,have you noticed it getting any worse the more miles you do ?

[Dcock]

Probs a good idea just to check the Throttle position sensor incase it was knocked some how in storage. Because it could be thinking your at a different throttle positioning and changing the timing etc Its very easy to check just follow this guide.

http://foc-u.co.uk/wiki/index.php/TPS_adjustment

[His Dudeness]

At such low mileage you can probably rule out mechanical failure. Sounds to me like its not getting fuel quick enough. Probably carb related from sitting up for so long but try a new fuel filter first. Also if you can start it and hold it at the stutter then throw some water on your downpipes and check if they all dry at the same rate or is one drying slower than the others. That will show you what cylinder is giving the problem

[Soapy]

hi john....welcome to the stuttering ccccccccclub,well you`ve covered most things....you did`nt mention float needle jet in the bottom of the carbs ,controls the flow of fuel to the float bowls,also worth checking the diaphrams,look for splits and make sure they are nice and flexible and that the needle is a nice smooth action....same symptons as my stutter,have you noticed it getting any worse the more miles you do ?

Hi red98. It was your problems that led me to the Forum. Yes it seems to get worse the more I thrash it. At the start of the ride it seems to be ok. Then after I have started to have fun and make sum rapid progress it will start to play up. I didn't check the float valves, Bugger. But everything was extremely clean. I am going to see if I can remove the Carb Tops without removing the Carbs themselves. I had a nightmare getting them out. I really struggled to get the forward throttle cable out. Any tips on that. Thanks for the quick reply.

[Soapy]

Probs a good idea just to check the Throttle position sensor incase it was knocked some how in storage. Because it could be thinking your at a different throttle positioning and changing the timing etc Its very easy to check just follow this guide.

http://foc-u.co.uk/wiki/index.php/TPS_adjustment

Thanks Dcock. Will do that tomorrow.

[dBfazer600]

I had something similar on my yb 100 way back. In the end i traced it to a dodgy earth as mine did not do it all the time but was more prominent when powering on (if thats possible of an 80's bike) the vibrations were shaking the earth to death and the sudden lost of power happened at any time until one day bugger stopped.
 
Do the obviouse with battery and check all is secure then work from that, its a pain in the ass.
 
Daz

[red98]

hi john....welcome to the stuttering ccccccccclub,well you`ve covered most things....you did`nt mention float needle jet in the bottom of the carbs ,controls the flow of fuel to the float bowls,also worth checking the diaphrams,look for splits and make sure they are nice and flexible and that the needle is a nice smooth action....same symptons as my stutter,have you noticed it getting any worse the more miles you do ?

Hi red98. It was your problems that led me to the Forum. Yes it seems to get worse the more I thrash it. At the start of the ride it seems to be ok. Then after I have started to have fun and make sum rapid progress it will start to play up. I didn't check the float valves, Bugger. But everything was extremely clean. I am going to see if I can remove the Carb Tops without removing the Carbs themselves. I had a nightmare getting them out. I really struggled to get the forward throttle cable out. Any tips on that. Thanks for the quick reply.

hi john......top of the outside carb will come off easy without taking the carbs off the bike.have a close look at diaphram , stretch it gently to see if there`s any splits and is nice and plyable (is that a word  )[size=78%]  also check that the slider is free to rise and fall in the body of the carb,whilst its out pop the needle out and note the position of the needle circlip...looking at one of the carbs will give a good idea on how the rest are,at that mileage i cant see it being a problem....yes the cables are tricky,pull the carbs out slaken both nuts and pull cable from metal bracket.thread cables down between carbs which will give you enough slack to hook the nipple out...helps if you have two pairs of hands [/size] [/size][size=78%].....its worth wrapping a bit of rag around the generator cover and resting the carbs on that while you remove the cables....i put a small scratch on mine when i first pulled them out [/size]
[/size]
[/size][size=78%] as db has mentioned check your electrics...lift the tank and have a good poke around the fuse box and behind the side panel , looking for loose connections and any moisture,check the cable that runs through the gennie housing,blue/yellow and three white wires mine were in a bad way and could be the cause of my stutter.......best to take the cover off and peel back the grommet for a proper look.......all simple checks which wont cost you anything [/size]   do you have a haynes manual ?[/size][size=78%]  [/size]

[Fazerider]

This sounds most likely to be the carb sliders not doing the right thing to me too. The fact that the bike runs OK at max power if you let it get there gradually indicates that fuel flow, sparks etc are up to the job, but opening the throttle quickly is resulting in the sliders jamming instead of rising at the correct rate.
With the carbs off, apply gentle pressure with your finger from the airbox side of the slider and you will be able to compare how freely they move. Chances are, one or two will be suffering more friction than the others because the PTFE coating has worn away.
When you remove the carbs disconnect the throttle cables at the handlebar first. With them loose at that end they can pull back an extra foot which gives  plenty of free play to get the carbs out... and then disconnecting from the pulley on the carb bank is simple.

[Soapy]

Thanks for all the help so far folks. I have just checked the TPS Sensor iaw Dcocks link. Disconnecting and reconnecting with the ignition on indicated 10000 on the Rev Counter. Adjusted to read 5100 (after spending £13 on a Security Bit set). What symptoms would have that given me and surely the bike would play up from the start? (can't understand how it could have moved the tamperproof screws were really tight). I've ordered a fuel filter just for peace of mind. I will try as you suggest red98 when the weather clears up. Unfortunately the weather isn't great at the moment and the bike is normally stored in the shed but there is no room to work on in there. Cheers John S

[Soapy]

This sounds most likely to be the carb sliders not doing the right thing to me too. The fact that the bike runs OK at max power if you let it get there gradually indicates that fuel flow, sparks etc are up to the job, but opening the throttle quickly is resulting in the sliders jamming instead of rising at the correct rate.
With the carbs off, apply gentle pressure with your finger from the airbox side of the slider and you will be able to compare how freely they move. Chances are, one or two will be suffering more friction than the others because the PTFE coating has worn away.
When you remove the carbs disconnect the throttle cables at the handlebar first. With them loose at that end they can pull back an extra foot which gives  plenty of free play to get the carbs out... and then disconnecting from the pulley on the carb bank is simple.

Thanks Fazerider. Another thing I should have checked when I had them out. I'm learning the hard way. The bike has only done 3500 miles so is it likely the coating would have worn away already?. But will try pushing the sliders up and see if there is anything obvious.

[Fazerider]

Hmm... must admit that sounds unlikely to be the cause of the problem at such a low mileage, I should have read your initial post more thoroughly.
It does still sound very much like a carb issue though. I wonder whether the springs might have weakened with time? The sliders rising up too fast would then give a reduced airflow over the jet and a leaner mixture. Does anyone know what the free length of the springs should be? It's not a spec listed in my Yamaha manual.

[Dcock]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

[darrsi]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Stuttering, or bogging down can be caused by too much air!
Happened to my bike when one of the carb rubbers folded in on itself when my mechanic refitted them, and number 3 inlet rubber was letting air in.
Everytime i went to overtake or generally give the throttle a bit of welly it would splutter all over the place and bog down.
I had to have the bike in elsewhere to get them to look at my carbs and they showed me what they found.

[Dcock]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Stuttering, or bogging down can be caused by too much air!
Happened to my bike when one of the carb rubbers folded in on itself when my mechanic refitted them, and number 3 inlet rubber was letting air in.
Everytime i went to overtake or generally give the throttle a bit of welly it would splutter all over the place and bog down.
I had to have the bike in elsewhere to get them to look at my carbs and they showed me what they found.

yeah true too lean mixture will do that as well. If that is case here, when he puts the choke on during the warm ride it should make the stuttering less noticeable as he would be increasing the fuel to air mixture. Either way wacking the choke on will hopefully show us something.. or nothing maybe.. Although if it was too lean that would cause idle hunting and make it difficult to start as well? Which I don't think he has mentioned. It will be interesting to see what's causing this!

[darrsi]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Stuttering, or bogging down can be caused by too much air!
Happened to my bike when one of the carb rubbers folded in on itself when my mechanic refitted them, and number 3 inlet rubber was letting air in.
Everytime i went to overtake or generally give the throttle a bit of welly it would splutter all over the place and bog down.
I had to have the bike in elsewhere to get them to look at my carbs and they showed me what they found.

yeah true too lean mixture will do that as well. If that is case here, when he puts the choke on during the warm ride it should make the stuttering less noticeable as he would be increasing the fuel to air mixture. Either way wacking the choke on will hopefully show us something.. or nothing maybe.. Although if it was too lean that would cause idle hunting and make it difficult to start as well? Which I don't think he has mentioned. It will be interesting to see what's causing this!

Not necessarily, i only noticed problems when opening the throttle right up, idle was fine and if i rode the bike easily there wasn't really an issue.
I even had 3 mechanics ride it and "they say" that they couldn't feel anything wrong, but obviously i ride the thing every day and knew damn well it wasn't right.
It cost me a fortune to get that sorted. As the carbs were off and i was booked into PDQ already i told him he may as well clean them up while i was there. 

[Dcock]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Stuttering, or bogging down can be caused by too much air!
Happened to my bike when one of the carb rubbers folded in on itself when my mechanic refitted them, and number 3 inlet rubber was letting air in.
Everytime i went to overtake or generally give the throttle a bit of welly it would splutter all over the place and bog down.
I had to have the bike in elsewhere to get them to look at my carbs and they showed me what they found.

yeah true too lean mixture will do that as well. If that is case here, when he puts the choke on during the warm ride it should make the stuttering less noticeable as he would be increasing the fuel to air mixture. Either way wacking the choke on will hopefully show us something.. or nothing maybe.. Although if it was too lean that would cause idle hunting and make it difficult to start as well? Which I don't think he has mentioned. It will be interesting to see what's causing this!

Not necessarily, i only noticed problems when opening the throttle right up, idle was fine and if i rode the bike easily there wasn't really an issue.
I even had 3 mechanics ride it and "they say" that they couldn't feel anything wrong, but obviously i ride the thing every day and knew damn well it wasn't right.
It cost me a fortune to get that sorted. As the carbs were off and i was booked into PDQ already i told him he may as well clean them up while i was there. 

Damn, that doesn't sound fun at all. did you need a new carb rubber or jus reposition the old one?

[darrsi]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Stuttering, or bogging down can be caused by too much air!
Happened to my bike when one of the carb rubbers folded in on itself when my mechanic refitted them, and number 3 inlet rubber was letting air in.
Everytime i went to overtake or generally give the throttle a bit of welly it would splutter all over the place and bog down.
I had to have the bike in elsewhere to get them to look at my carbs and they showed me what they found.

yeah true too lean mixture will do that as well. If that is case here, when he puts the choke on during the warm ride it should make the stuttering less noticeable as he would be increasing the fuel to air mixture. Either way wacking the choke on will hopefully show us something.. or nothing maybe.. Although if it was too lean that would cause idle hunting and make it difficult to start as well? Which I don't think he has mentioned. It will be interesting to see what's causing this!

Not necessarily, i only noticed problems when opening the throttle right up, idle was fine and if i rode the bike easily there wasn't really an issue.
I even had 3 mechanics ride it and "they say" that they couldn't feel anything wrong, but obviously i ride the thing every day and knew damn well it wasn't right.
It cost me a fortune to get that sorted. As the carbs were off and i was booked into PDQ already i told him he may as well clean them up while i was there. 

Damn, that doesn't sound fun at all. did you need a new carb rubber or jus reposition the old one?

It was literally just folded over in on itself by about an inch, he showed me it first then just unfolded it.
As it was number 3 carb it would never have have been seen or noticed unless it was removed, and i don't know how big the gap was letting air in, but i s'pose any air at all will make it misbehave.
It was accidental and just one of those things, BUT, i was really disappointed that 3 very experienced people couldn't feel the problem because quite frankly it was bloody obvious that it wasn't right in my opinion!
I went back to them 3 or 4 times then gave up wasting my time and took it to PDQ instead.

[Soapy]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Information overload at the moment. But all ideas gratefully received. I am going to try it again tomorrow before I go any further. I normally start the bike on choke and reduce it over a couple of minutes. Then ride off with no choke. I'm sure when I rode it the other day, initially the bike seemed to be ok but when I started to give it the beans, that is when it started to bog down.
Plan of attack tomorrow weather permitting.
1. Try riding it gently all the time see if it behaves
2. Ride hard and try and get it to stutter. If it does, try putting the choke on to see if it makes any difference.
3. If it does stutter I'm going to replace the fuel filter and check out the No4 Diaphragm. If that doesn't help.
5.Set fire to her. Only kidding 

[Soapy]

Just to clarify, when the bike is cold, if you go full throttle it will go up the rev range fine with no stuttering? But once the bike is warm it will stutter as soon as you give it full throttle? Are you using choke when it's cold? If not put some choke on when its cold and then give it full throttle. If it stutters, then this may point towards over fuelling or not enough air  as the problem when the engine is up to temperature. Also you can test this again by seeing if putting choke on when the bike is hot makes the stutter worse. Let us know what happens when you try this. Cheers.

Stuttering, or bogging down can be caused by too much air!
Happened to my bike when one of the carb rubbers folded in on itself when my mechanic refitted them, and number 3 inlet rubber was letting air in.
Everytime i went to overtake or generally give the throttle a bit of welly it would splutter all over the place and bog down.
I had to have the bike in elsewhere to get them to look at my carbs and they showed me what they found.

yeah true too lean mixture will do that as well. If that is case here, when he puts the choke on during the warm ride it should make the stuttering less noticeable as he would be increasing the fuel to air mixture. Either way wacking the choke on will hopefully show us something.. or nothing maybe.. Although if it was too lean that would cause idle hunting and make it difficult to start as well? Which I don't think he has mentioned. It will be interesting to see what's causing this!

Not necessarily, i only noticed problems when opening the throttle right up, idle was fine and if i rode the bike easily there wasn't really an issue.
I even had 3 mechanics ride it and "they say" that they couldn't feel anything wrong, but obviously i ride the thing every day and knew damn well it wasn't right.
It cost me a fortune to get that sorted. As the carbs were off and i was booked into PDQ already i told him he may as well clean them up while i was there. 

Damn, that doesn't sound fun at all. did you need a new carb rubber or jus reposition the old one?

It was literally just folded over in on itself by about an inch, he showed me it first then just unfolded it.
As it was number 3 carb it would never have have been seen or noticed unless it was removed, and i don't know how big the gap was letting air in, but i s'pose any air at all will make it misbehave.
It was accidental and just one of those things, BUT, i was really disappointed that 3 very experienced people couldn't feel the problem because quite frankly it was bloody obvious that it wasn't right in my opinion!
I went back to them 3 or 4 times then gave up wasting my time and took it to PDQ instead.

Hi Darrsi. My bike was doing it before I removed the carbs. I have given the inlet rubbers a look and there isn't any sign of cracking etc. It looks like I may be taking the carbs of again. If i do I'm going to take the inlet and airbox rubbers off for close inspection.
I'll report back tomorrow. Thanks again everybody.

[darrsi]

I very rarely need to use the choke, but if you use it regularly is it possible that it could be stuck on a little bit rather than being totally switched off?

[Soapy]

Spent a bit more time on the bike today. Ran it for nearly five miles with no issues. Whilst it was ok tried putting the choke on to see if it made any difference. It didn't. Tried going down to 3000 revs several times and every time it picked up ok. Got to about 5 miles and she started to play up. Pulling any more than 1/4 throttle resulted in severe stuttering. Tried putting on the choke whilst the stuttering was happening, didn't make any difference. Road her home.
Replaced fuel filter and a friend lent me a set of vacuum gauges to check the carb balance. Had to adjust 3 & 4 ever so slightly. Bike was now getting hot and fan was running as expected. Blipping the throttle when the bike is hot results in a little stutter as you flick the throttle.
After the balance I thought I would remove No's 1 & 4 Diaphragms. They look and feel fine. The rubber is soft and supple and no signs of holes. I also removed the plugs and apart from being very slightly black they were fine.
After I had put everything back to together the bike had cooled down a bit. I started her up and blipped the throttle without any real sign of the stutter. Got to be heat/time related.
I'm now leaning more to an ignition or some kind of electrical fault. If it was a carb/jets/diaphragm issue then surely it would occur from the start.
What effect would a pick up sensor breaking down/overheating have?
Have a short couple of video's I took on my Iphone of the carb balance but don't know how to load them.
 
 
 
 
 
 
 
 


 
 
 

[unfazed]

Check the rubber plugs on the vacuum take of points as they can crack and go unnoticed.
Check the wires to the pickup where it enters the alternator cover.
It is good idea is to take all connectors apart and spray with WD40 while checking for chaffed wiring.
A common place for corrosion is on the fuel pump connector and the pickup up connector.

[Soapy]

Check the rubber plugs on the vacuum take of points as they can crack and go unnoticed.
Check the wires to the pickup where it enters the alternator cover.
It is good idea is to take all connectors apart and spray with WD40 while checking for chaffed wiring.
A common place for corrosion is on the fuel pump connector and the pickup up connector.

Hi Unfazed. I checked the Vacuum plugs when I did the carb balance. They look ok. Visually checked the loom from the Pick Up Coil we're it comes out of the LH Engine Cover. Also had a look at the connectors under the LH side cover. Nothing obvious there.
The Haynes manual states if you want to replace the pick up coil as its part of the Alternator it has to be replaced as well. Need to be sure it's the problem as that will not be cheap to buy.