fuel feed problem?

kiltman

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Apr 27, 2013
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Stratford, Ontario Canada
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2002,ST1100ABS
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8826
2 shots in the dark. When you fill up and remove the gas cap is there a swoosh of air escaping? If not you may have a faulty gas cap. This can affect fuel delivery.
the second is that it could be electrical, have a look at the red wire going into the main relay on the left side, make sure that connection isn't compromised. Another spot to check is also on the left side by the green connector for the side stand, is a main red power wire just inside the up member of the frame. On my bike the insulation wore off due to vibration and rubbing on the frame which could ground out depending on the condition.
These are remote possibilities but very easy to check
 
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dave120v
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Dec 18, 2016
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chard
Hi Kiltman will look thanks I am up to try anything but as I said in my last post I may be expecting too much but it feels if its holding back Dave
 
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Grand Junction, Colo.
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92 ST1100
Since you stated apparently having carbs off, etc. your DEFINITELY going to have to re-set idle mixtures and re-sync carbs. Having not done that WILL create the scenario your bike is having;). Setting idle mixture done using lean-drop method: With motor warmed up, back a mixture screw out several turns, then slowly screw it in till exhaust sound has slightest change.......then back screw out 1/8th and no more than a quarter turn.........go to next one,etc.......THEN sync. carbs;).
 
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dave120v
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Dec 18, 2016
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chard
Hi Brant, I concur with that so when I had fitted the replacement carbs took it to my local garage they balanced the carbs but thanks for the set up info.
It seems as if opening the throttle too much makes the bike falter backing off the throttle allows it to "catch up" but its very difficult to describe.
 
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dave120v
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chard
in reply to kiltman, yes do get a whoosh when releasing the fuel cap not checked the other yet thanks
 
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soCal
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'97 ST1100
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687
It seems as if opening the throttle too much makes the bike falter backing off the throttle allows it to "catch up" but its very difficult to describe.
Your original description made it sound like it might be a more abrupt loss of power, like with ignition cutout, or also possibly fuel related. But this description sounds like its a more gradual power loss, as in fuel delivery. So is the current thought that its a fuel delivery issue?
 
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dave120v
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Dec 18, 2016
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chard
Its very hard to describe, as far as I can now tell it cant be fuel from the pump/filter side as I have bypassed all that and checked the pump/flow. It mainly manifests its self on the overtake scenario you pull out open the throttle it picks up gets to about 4-6000 rpm then holds back till about 7-8k if you open the throttle more nothing happens if you back off it gets in sync but wants slow opening of the throttle just when you want more. Its almost like its missing a cylinder that's why I did the coils/leads/plugs. I just wonder if I am just asking too much. As I said in my earlier posts its my first pan and nothing to judge it against need another Pan rider to have a go and tell me whether I am just being over enthusiastic and expecting too much. Dave
 
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soCal
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'97 ST1100
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687
You're not asking too much, it should pull cleanly to redline even though its not exactly a powerhouse of an engine to begin with. The only other thing I can think of is look for corrosion/damage in the electrical connector paths to the coils, as you never swapped those out, just the coils/wires. Not sure how the spark pulse is generated, never had to troubleshoot that, maybe the timing isn't advancing properly at higher RPM? But it sounds like its OK at 7-8k, so don't know if it could advance properly at 7-8k but not around 6k.
 
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Vernon BC Canada
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09 ST1300
I have read your post and replies with interest. What this seems like you are describing to me is a lean spot in the power curve, as this will feel like the engine is holding back and unable to power through it with more throttle. If you back off a bit and allow the rpms to change higher or lower it will then continue pulling. As you say it pulls clean and strong at 7k then that rules out fuel delivery and supply issues - it's getting fuel. I feel an ignition problem would present itself at a lower rpm if not just off idle, when at that rpm if throttle is abruptly opened and cylinder pressures are at their highest then kilovolt demand on the coils is highest. This would happen much lower than 4-5k so I think that rules out ignition. I'm not a bike carb tuner but an auto mech, and I have a very similar experience with an old FZ750. It had the same flat spot you describe, and an aftermarket exhaust that I felt was casuing a lean condition at that certain rpm range. What I did to verify this was made a homemade baffelt o clamp over the exhasut tip to act as a restriction, and this for sure changed/eliminated the flat spot. It confirmed for me that the aftermarket exhaust had changed the breathing and scavenging traits designed in by the manufacturer in a very negative way. Something to try anyway to at least get you headed in the right direction. If this ends up being the case you will need some help from an experienced tuner with access to a dyno or revert to stock exhaust. A lot of people have a misconception that simply freeing up flow through intake and exhaust will net in more power, this is simply not the case. Certainly efi is better equipped to maintain fuel control to an extent when these mods are done but carbs not so much so. I hope this helps and a Merry Christmas to you
 
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East Anglia, England
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ST1100X
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#1702
Geoff has suggested an exhaust restrictor might work - here's mine fitted to a Motad, made from 1" alloy tube - not for your problem, but to reduce the 'drone' at cruising speed....

...Roger
 

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dave120v
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Dec 18, 2016
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chard
Hi Roger,
Thanks for the photo, an d nicely built thermal model too,RC? Another fellow modeller I assume! so this is fitted in the silencer I assume at the tail pipe? mine has removable baffles I did try removing it and don't think it made any difference to the problem, however I will remove them again and see, it should make it worse if I am reading it right. I don't really want to buy another system just to find out that's not the problem. What I really need is another bike to compare it too, just don't know anyone else around here with a pan, Having said that I have a mate with the new 1300 but that's not really like for like. Its a very difficult problem to describe exactly, but when its occurs if you open the throttle more nothing much happens you have to wind off the throttle and let everything catch up it would seem. if you rev it on the stand it revs fine. Everyone here is very helpful and I am grateful for that, the problem kind of outs me off riding it when I have the choice of other bikes to ride which is a shame as its a nice ride. Dave
 
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dave120v
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chard
someone else suggested to me lifting all the main jets one notch to see if its leaning out too much, any thoughts on this?
 
Joined
Aug 9, 2010
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Vernon BC Canada
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09 ST1300
lifting all the main jets one notch to see if its leaning out too much,
This may change slightly where the flat spot is occuring, but the needle only has effect on mixture between 1/4 to about 3/4 throttle opening. At WOT it would be the same regardless of clip position. At wide open throttle you will be on the main jets. I would see first if doing anything with the exhaust changes the behaviour of this problem to make sure we are barking up the right tree lol.
 
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dave120v
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chard
Hi Thanks for that, I will take out the baffles at the rear first and see what the changes are.
I will also check the connections on the ECU can anyone tell me the location of the ECU, I may change this as well as I have seen one on Ebay for ?30 this would eliminate this and if its not that I can sell it back with confidence that that's not the problem.
Thanks Again for all the help
Dave
 
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dave120v
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chard
Thanks, I am now waiting time to get out on the road again, I still need to locate the ecu any ideas?
Dave
 
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Auckland, New Zealand
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2005 ST1300
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Thanks, I am now waiting time to get out on the road again, I still need to locate the ecu any ideas?
Dave
Remove the fake tank and the left hand cover/storage pocket, and you can reach the ECU which should be tucked into the fairing in front. The ECU sits in a rubber sleeve mount that you can unhook from the subframe and then lift the unit out then disconnect it from the loom.
 
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dave120v
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chard
Brilliant description Terry thanks will get on with that asap just need time and better weather for testing will keep you posted
 
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dave120v
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Dec 18, 2016
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chard
Hi Guys,
I have just had a thought about this problem and wondered if it could be to do with the advance and retard of the timing, does anyone know how this is done on the Pan? I think this would give this type of symptom
Thanks
Dave
 
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