fuel feed problem?

Hi This is a bit of a saga on my st 1100 pan, basically it runs ok but if I demand heavy acceleration on say an overtake there is hesitation at around 4-5k plus its almost like fuel starvation or possibly loosing a cylinder or something it fells like its holding back, but if I am gentle up through the speed range it appears fine.
I thought at first it was carbs so i managed to buy a complete set of secondhand carbs went through them and checked them out diaphragms jets etc all were good so I fitted them and took them to my local garage to balance up for me, all was fine there except it still had the same problem, it seems fine on the rev up off load when your on the stand. So my next thought was perhaps it was loosing a spark under load so I put new plugs still the same so I next put a secondhand set of coils just in case one was faulty under load but still the same. Now I am thinking that it may be a fuel feed problem and I am about to undertake stripping down the fuel system to check it all out but I thought I would bounce it off you guys to see if there are any of you out there that have had a similar problem or have any ideas as I am not sure what it could be.

Its spoiling my riding of what would otherwise be a fine bike, so over to you

Thanks
dave

Dave,
You don't mention the fuel filter, have you replaced that.
Upt'North.

No I have not and not sure where it is also is there anyway I can set this post to allow it to update me via email so I know someone has replied?
Thanks for your reply
Dave

Dave I had something like that on my ST11 when I returned it to the road after 10 years parked by the PO. Ultimately I tracked down a dirty connector feeding power to the ECU which was causing weak sparks. I diagnosed this following the service manual procedures, there are tests there for voltage to the ECU and also resistance in the coils and spark leads. Check the connectors behind the steering head, in my case the big red one was the problem. Much easier to access these with the carbs out.

Dave, remove the false tank turtletop(2 allen head bolts at front topside). fuel filter lays right at front rightside of fuel tank. Also, diaphragm fuel shut-off will at times not function properly. It can easily be by-passed(just follow fuel line from tank).

Hi Guys
Thanks for the info I will follow these up as soon as I get a chance

Try a quick bypass of the vac. fuel valve while you've got it apart for the fuel filter. Just move a hose or 2.

http://www.st-riders.net/index.php?topic=3919.0

Don't forget to plug the vac. hose. The valve is on a bracket mounted to the air filter where your right knee would be. I used one of the screws that holds the bracket to the filter housing. It screws into the hose nicely.

Dave, remove the false tank turtletop (2 allen head bolts at front topside). fuel filter lays right at front rightside of fuel tank.

Click to expand...

I think there are a couple hex head screws (10mm wrench) that are under the side covers.

Dealing about fuel system, after inspecting filter and vac (easy), don't forget the fuel pump, when it gets old and the fuel flow is weak, can generates the simptoms you described.

Hi Great help guys thanks I will endeavour to try all of this as its spoiling a good bike, what should the fuel flow be I suppose the easy way is to just feed power to the pump remotely and then take the output and pump it into a container and see how it flows but what is a good flow rate, I don't have a proper Honda workshop manual or a Haynes one but I do have a fair mechanical/electrical background
Really guys thanks for all the help just need time in the garage but Xmas is spoiling my fun!
Dave

Hi I have had the turtle deck off a few times so no problem there, as I said changed the carbs and the coils and spark plugs too! all in vain so far.

It sounds spark related to me, I've seen the same thing a on cars. Under no load the spark demand is different, so it revs cleanly in neutral, but put a load on it and the cylinder pressure changes the spark requirement, and you get misfire symptoms. When you changed the coils, did you re-use the same plug lead wires and caps, or did the spare coils have the wires/caps already on them? If you re-used the old wires/caps, the problem may still be lurking in either the wires or caps.

I have just one other thought and its a long shot, its been fitted with aftermarket stainless system with silencers don't suppose this could cause a problem, would not expect so but its a thought
Dave

Hi Dwalby,
I fitted complete replacement coils and leads set admittedly second hand but to get two sets with same problem fairly unlikely, but thanks for the idea, its not to say that its not possible for sure!

Considering all the things you have done it may not have anything to do with fuel or ignition. Could it possibly be clutch slippage as you open it up close to maximum torque point?

Hi I can be sure its not that you can feel the engine holding back but everything should be considered but clutch slippage would have the engine rpm increasing with not road speed increase and this is not happening as far as I can tell but thanks thanks

dave120v said:

Hi Great help guys thanks I will endeavour to try all of this as its spoiling a good bike, what should the fuel flow be I suppose the easy way is to just feed power to the pump remotely and then take the output and pump it into a container and see how it flows but what is a good flow rate, I don't have a proper Honda workshop manual or a Haynes one but I do have a fair mechanical/electrical background
Really guys thanks for all the help just need time in the garage but Xmas is spoiling my fun!
Dave

Click to expand...

I've read that a simple current test at the pump electrical connection usually shows symptoms of a weak pump. Remove one of the leads to the pump and put a meter in series in the path to measure the current draw. Apparently a weak pump will draw 0.6-0.7A, while a good pump will draw 1.2A. Also, forum members have taken weak pumps apart, cleaned up corrosion on the commutator/brushes and gotten them to work again, and the current draw went back to 1.2A after the cleaning. This test takes literally 1 minute, remove the seat, remove the electrical lead, place meter in path (also helps if you have alligator clip meter leads).

Also, +1 on bypassing the vacuum fuel shutoff valve while you're at it, another easy task to rule out that component.

brilliant will try that first thanks
dave

dave120v said:

Hi Great help guys thanks I will endeavour to try all of this as its spoiling a good bike, what should the fuel flow be I suppose the easy way is to just feed power to the pump remotely and then take the output and pump it into a container and see how it flows but what is a good flow rate, I don't have a proper Honda workshop manual or a Haynes one but I do have a fair mechanical/electrical background
Really guys thanks for all the help just need time in the garage but Xmas is spoiling my fun!
Dave

Click to expand...

If you want to perform the test, remember that when you turn on the key, the pump runs for a couple of seconds, than stops and restart only if you start up the engine. If you wanto to see a decent flow into an external container you have to power the pump via the connectors you find on the tank top


here is something from the internet

https://www.youtube.com/watch?v=U965Q5fvPK8

Hi Again, well I have been busy and will try to upload some pictures, I have checked the fuel pump it supplies at 1.2-1.3 amps so clean and green I disconnected the diaphragm fuel stop and checked it out by sucking on the vacuum pipe outlet and then blew down the fuel supply line all good but I did bypass all of this and bypassed the filter which again was flowing freely
I took it out for a ride and its better I think but it still seems to be holding back, I just wonder if I am expecting too much from the bike, Having never owned a pan before I have nothing to compare it with. Just wondered if there was a member in somerset who would willing to meet up and test the bike just to see if I am just chasing fairies so to speak
Hope the uploaded photos work
Dave