Engine splutters on hard acceleration

Gooed said:
If running with the filler cap open fixed the problem, what would be the fault? Thanks.
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I am assuming that the GS has a vaguely similar fuel system to the RT and there is a rubber breather pipe exiting the bottom of the bike somewhere near the footpegs. Bikes destined for North America have a small charcoal canister in this pipe to trap petrol fumes and any spillage from a drop, as well as equalising ambient and tank pressure. European bikes do not require this and so the upstream and downstream bits are just joined together with a short piece of internal plastic tube rather than a continuous one - this collects debris over time and if it is partially blocked will cause the fuel pump to struggle against the vacuum now in the tank

The easiest remedy is feeding a new length of rubber tubing from the spigot down through the frame and leaving the existing one in place

(As an aside, the RT’s plastic tank can deform under these condition and after a long fast run it will jam up against the left strut giving the false impression of a completely flat front tire - the temporary cure is to pop the filler cap open occasionally to allow the tank to breathe DAMHIK)
 
Kritou said:
(As an aside, the RT’s plastic tank can deform under these condition and after a long fast run it will jam up against the left strut giving the false impression of a completely flat front tire - the temporary cure is to pop the filler cap open occasionally to allow the tank to breathe DAMHIK)
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the joy of ethanol filth in modern fuels - it distorts / expands plastic and grows bugs that excrete acetic acid - together with water ethanol absorbs from the atmosphere, the acetic acid rots metal and the water helps it corrode, so your pump, fittings and injectors help sell new motorcycles

everything is connected you just have to join in how sick people are - all the while marketed as it helps save the planet - so a 6% min increase in fuel consumption, plus eventually forcing already manufactured motorcycles off the road - so we can drive up sales and puke another 20 t of carbon pollution for each designed to last 4 years new motorcycle produced
 
Thanks Popell, I’ve gone and just bought new ignition coils (non-OEM ones off spark plugs.co.uk)
 
Gooed said:
If running with the filler cap open fixed the problem, what would be the fault? Thanks.
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Just a suggestion from an amateur tinkerer.
Partially blocked fuel tank breather valve or associated hoses, possibly kinked ?
 

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Gooed said:
Thanks Popell, I’ve gone and just bought new ignition coils (non-OEM ones off spark plugs.co.uk)
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Did you get the 'Champion' branded could? They're actually OEM

Sent from my SM-G975F using Tapatalk
 
Only just back into the forum after a break. But late to the party.

My first two thoughts were Steppers > water in the fuel. Or the coils...

Sounds like you're on it . Ref the breather and fuel cap open business, if the breather is blocked, as fuel is used and the tank fuel volume reduces a vacuum is created (if the breather is blocked), which on high demand means the pump can wrest enough fuel. Opening the file cap is an instant cure

Sent from my SM-G975F using Tapatalk
 
***** Coincidence *******

I have a 1200GS 2006 with EXACTLY the same issue!
Replaced coils, plugs, TPS and checked Valve clearances, fuel breather pipes (fresh fuel in tank) etc.
No faults using GS-911
Now looking at fuel pump

Thanks to all who have offered possible solutions to this issue.
 
If valves are in check,cables are in good order, fuel is fresh, plugs are new and alternator is working.....

Replace all coils, plugs and Lamba sensors on a 15-20 year old GS with average mileage as a matter of course. Even if they're not faulty, they're past their best.

You can't accurately test the coils (even when I was in a main dealer workshop with every toy and diagnostic tool you can think of)

Same with the lambda sensors, unless you have a oscilloscope. They don't produce faults unless they short out and they are a cause of numerous running problems.

Steppers are easily removed and cleaned. Calibrate (and listen to them move) using Motoscan.

Injectors can be removed when bike is running to check spray pattern.

Fuel pump controller is just an on/off. They generally don't cause your issues and they are incredibly reliable post recall.

Fuel pump is possibility, you can remove and check it's filter but I've yet to see one blocked.
 
MotoRevive said:
Fuel pump is possibility, you can remove and check it's filter but I've yet to see one blocked.
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The 1200 has two fuel filters: One is a mesh strainer bag on the pump suction, its obvious when you remove the pump housing. The other is a fuel discharge filter hidden inside the pump delivery housing, its a permanent part of the plastic moulding. It becomes slowly blocked over the years reducing fuel flow to the injectors. Some people have managed to back-flush them, the best option is to drill out the filter screen with an 8mm drill bit, flush the debris out then fit an external high pressure filter designed for the 1150GS.

If you look at the links I posted previously in this thread in reply #10 you will find the article on how to remove the pump housing, drill out the filter and restore peak fuel flow.
 
Regarding fuel pump on my post #20.
The replacement ebay fuel pump has now failed after 32K miles.
Yesterday on a 260 mile ride topped up the tank at 110 miles, at 200 miles I noticed the fuel pressure on the gauge had dropped from 60 to 50psi over the next 50 miles it continued to drop but in a haphazard way.
10 miles from home and it was down to 20 psi and struggling to run, had to accelerate very gently until it finally cut out at a junction.
Switched the ignition off to let the traffic clear so that I could join the main road and try to make some progress, On switching the ignition on the pressure rose to 30 psi the bike started the pressure slowly rose to 50 to 60 psi and ran ok until I got home.
GS911 showed no fault codes.
Tank breathers clear.
Pump screen clear.
The stock fuel filter is already bypassed.
Tried 2 different FPC`s
Pressure test pump without regulator in circuit 60psi it was 120 psi when new.
Changed the pump over for a second hand OEM pump that I had on the shelf ( history unknown) shows 70 psi without regulator and circuit blanked off, 60 psi with regulator in circuit.
Could not find much information on the more expensive pumps so have ordered the same again now cheaper down to £24 so will treat it as a service part and change it every 30K miles.
I assume the brushes in the pump were worn or sticking or the vanes were sticking and worn. I will cut it open and have a look.
Just to confirm that when the pressure was between 30 and 40 psi it was popping and misfiring as if the coils were breaking down under acceleration.

SPcWamG.jpg
 
Decided to take the pump apart to see what the problem was.
The ends of the pump are swaged so cut this back in the lathe.
The turbine rotor and housing looked ok but the commutator and brushes are very badly worn so 30K miles is all I will expect from one of these pumps.
The last pump that I removed was OEM had done 43 K miles and was down to 30 psi , so I decided to strip it as was was of no further use.
Cut the swaged end back, the brushes and commutator are still serviceable but the turbine / rotor housing are worn.
Photos of dismantling the Ebay ( last) pump, the internals and the worn commutator.

PwFIruw.jpg

18D0MrJ.jpg

azp6uXb.jpg
 
Cheers for the info Chris.

I wonder how my more expensive Quantum aftermarket fuel pump will fare over time, but if it lasts over 30k I am not too worried as it's about another ten years worth ( I have several bikes so less use daily on each).
 
So I finally replaced all 4 ignition coils and it’s fixed the problem. Thanks for all the advice.
 
Gooed said:
So I finally replaced all 4 ignition coils and it’s fixed the problem. Thanks for all the advice.
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It's always bloody coils....

With every old GS that comes into my shop with running problems, I pretty much refuse to start pulling apart things that customers have read on forums until all four coils have been swapped out.

All four coils can be replaced for the same cost as having a tech scratch his head (and arse) for two hours looking at things which are highly unlikely to have failed.
 
gazza12adv said:
When I had a coil breaking down it was running fine on light throttle opening up to about 60 mph. Wider throttle openings it would stutter and missfire. I replaced both coils and it was fine after.
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Popell said:
Let us know if that sorts it.
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Popell said:
Well done, I guessed correctly but certainly learnt a bit more about the inner workings re the fuel side of things.
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You're not the only one.
Glad you got it sorted sir.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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