Last night (very wet) I filled up with petrol and hit the motorway. Everything was fine until I attempted to roll on the power from about 60mph. As soon as I fully opened the throttle, the bike surged and died, surged and died, and so on and the bike consequently took a long time to get up to speed. I repeated this a few times and it happened the same each time.
I then tried to accelerate gently by only hold the throttle open slightly and it was fine - the bike cruised up to 90 without a hitch. Again, going back to fully opening the throttle caused the surging/dying.
By the end of my 40 mile commute, and also this morning, the bike was/is fine.
I had a similar feel prior to my alps trip. brisk spark plugs the problem and they were new. put the old ones back in and all ok then the surging misfire feeling came back (old plugs)
Water in your fuel system! I had those symptoms a couple of months back. Drained tank, new fuel filter, disconnected as much of the fuel plumbing as possible - above the injectors too and allow it all to dry out. Fresh petrol with a measure of injector cleaner. Mine now runs better than ever, more responsive.
Failing that, someone suggested I might have a damaged wire, possibly at the base of the ignition switch or in the bundle under the left panel near the fuse box, they chafe through there.
Mine did exactly this on the way to the Mondello SB's a few weeks ago...I wrote about it here then.
Similar conditions before ie. very wet.
Despite going back to dealer cos still under warranty, never really got to the bottom of it. pidcocks changed the throttle pot and said it might be that, I wasn't sure cos it did suit all the symptoms.
Has not recured in the last 2000+ miles (some of which was in the rain)
With hindsight I suspect one of two things;
1. Water got into the tank somehow and was spat out eventually...why the fuel filter wasn'twrecked by this I can't tell you but neither Pidcocks or I have changed it.
2. Water got in somewhere up high like maybe the hall sensor connection. Finally dried out...couldn't find any sign of water around plugs or side stand or fuse or relays..damn near stripped the thing back to frame at one point.
Sorry can't be more help, but if you find a cause please post it as I am still not really sure why the fault happened, was really bad on and off for a day or so and then has never recuured!
Check the spark plug gap!!! Oh hang on, how do you do that
Nick wrote:I had a similar feel prior to my alps trip. brisk spark plugs the problem and they were new. put the old ones back in and all ok then the surging misfire feeling came back (old plugs)
Bike did it again this morning and was also a little lumpy in traffic before I hit the motorway.
As others have have said, I'm suspecting water is the cause but I am a little puzzled as to why it would only occur when the throttle is opened hard. The other thing about the water issue is that it has been raining pretty much solid for weeks it seems so the bike is probably still not dry (kept outside under a cover as well). If we get a few days in the sun it may sort itself.
Anyway, bike maintanence is definately not my thing. I'm getting it in for a service in a couple of weeks so I'll post back here with a solution should the guys at Fowlers come up with one.
Daz555 wrote:Ok, bike is back from service so we'll see what happens next time the bike gets very wet.
The only think unusual about the service (no problems found otherwise) is the following line on the report:
"Injector body take off clips and caps had perished - these have been replaced on service as will improve bike running."
Any idea what this means, and is it likely to make any difference?
they are the small black rubber caps on under side of throttle bodies. If they were perished, air would have been able to get sucked in giving a weak mixture and subsequent erratic running.
Honda VFR750 FV 1997 Red and dirty, 130K miles.
Honda VFR800 Xf Crossrunner 2016 White and dirty, 120K miles.
bigblackfalco wrote:They are the small black rubber caps on under side of throttle bodies. If they were perished, air would have been able to get sucked in giving a weak mixture and subsequent erratic running.
BINGO!
Nice one. Cheers for the info. Hopefully this may sort my occasional lumpy running at low revs and also the problem I posted at the start of the thread.
Further to loosing two sets of these rubber caps, I have now made a clip to hold them in place.
I found a strip of stainless in an old office file; two metal prongs hold the paper in place, this strip drops on the paper, bend prongs flat.
Cut the strip about 5 cm in from the end, bent it into starting handle shape, trapped cut end under inlet manifold retainer clip and the other end with the hole now holds the rubber cap in place. Repeated for the other side. = peace of mind.
oyster wrote:Further to loosing two sets of these rubber caps, I have now made a clip to hold them in place.
I found a strip of stainless in an old office file; two metal prongs hold the paper in place, this strip drops on the paper, bend prongs flat.
Cut the strip about 5 cm in from the end, bent it into starting handle shape, trapped cut end under inlet manifold retainer clip and the other end with the hole now holds the rubber cap in place. Repeated for the other side. = peace of mind.
Nice idea.
As it happens, the mechanic at Fowlers in Bristol fitted caps different to standard. The new caps have spring clips holding them in place.
Arse. Problem is back again - right after the bike got thoroughly soaked. Water must be getting in somewhere.
Can anyone recommend a decent BMW service place in Bristol? Fowlers are not too BMW savvy to be honest and have admitted as much. Motorrad in Bristol are booked out until middle of Sept.
Having a problem like this but not just in the wet. Seems as soon as the engine gets warm it has hesitancy on larger throttle openings. Not good when over taking.
I have changed the plugs done the valves about 3000 miles ago and also balanced the throttle bodies with the twin max.
I did the fuel filter also. (its running better at idle now ) but still same problem. (pig of a job)
Cannot see any cracks in the air inlets to cylinders or take off's from vacuum's
I have noticed corrosion on one of the HT leads and wonder if I have a misfire caused by this. taped it up with electrical tape. but not had chance to test yet.
Arse. Problem is back again - right after the bike got thoroughly soaked. Water must be getting in somewhere.