Bonneville Speed drop?

I'm wondering if any of you people have have experienced this problem and if so what caused it:-

Yesterday afternoon I was on the motorway doing about 80mph maybe a little more when the speedo showed the speed drop by around 10mph but the physical speed didn't seem to alter, the rev counter also started to fluctuate up and down after a few seconds it was back to normal and the rev counter stayed stable. I pulled off the motorway after about 6 miles and the idle speed had risen from 1000rpm to about 1400rpm so I altered the idle speed back down to around 1000rpm using the adjuster. Whilst on the move the engine felt like it was trying to cut when the throttle was held at about 30-35 mph. there was no real loss off power and if I accelerated it still pulled like a train and the cutting/missing wasn't evident. after bout 6 miles when I pulled up at the lights the idle dropped back to 800rpm so I adjusted accordingly. The Bonneville does seem to run hot so I was wondering if this may be the issue and me flogging it on the motorway was what had caused it. Once home I let the engine cool and it starts alright, although I haven't taken it on the road yet I've got a feeling that it may have been a glitch or bad fuel. Incidentally I had refueled 20 miles previously so it's possible that it could have been some crap that has been pushed through but I understand the Bonnie has a fuel filter so this is unlikely. I phoned my local dealer who I purchased the bike from and they said that it could need the throttle balancing and that it would be looked at at the 6000 mile service.

The bike is a 2011 Bonneville se that has covered a little less than 5000 miles in standard trim with all the air injection system still intact and with the OEM exhaust system and afaik the standard ECU map.

Any advice/thoughts welcome. Thanks in advance.

 

Hi Eric, the first thing I would be checking are the short rubber tubes which attach the throttle bodies to the solid plastic MAP pipes. If one of those split or perished you'll get poor running.

Can't explain the electrical malfunctions though.

 

Cheers for the reply Dave, I'll check the pipes when I get home from work later. It would be great if it's just something simple like that.

 

Dave I couldn't find anything physically amiss with a visual inspection, I'm hoping that the ECU will have logged a fault when it happened and that I will be able to get a clue when I plug the bike into the Laptop - I'm now thinking it could be one of the sensors going down or the throttle position sensor needing a tweek. The plot thickens!

 

Tune ECU didn't show any faults logged however - this morning on my way to work the bike completely cut out at 60 on a duel carriageway. I was in the right hand lane and lost all power to the point that the indicators didn't work, managed to restart it but at about 10mph it was showing 50 on the speedo. and the revs where all over the place. Found out what it was though.... Never ignore the ISO model because it can apply to almost anything. :?)

 

Don't understand? Glad you've found the problem but it might help to say a little more clearly what it was?

 

Thought I'd leave you all in suspense for a while Dave ;?). The bloody lead was loose to the negative terminal on the battery. Layer one of the ISO Model, it always pays to check the basics first. I've checked the charging circuit and that has survived so over all I've been a lucky bastard, the voltage spikes could have caused all sorts of damage to components like the ECU and rectifier. The ECU hadn't logged a fault even when the voltage was cutting in and out which I find a little strange. Anyway it's running like a sawing machine again. Thanks for showing an interest man.

 

Glad you got it sorted and no adverse effects

 

You WERE bloody lucky there Eric !!!! Good to hear it was something simple - I'll bet we all go out and check our battery terminals now !!!!!!

 

It was a schoolboy error. I refitted the battery at the start of spring and hadn't tightened the negative terminal enough and over the weeks it had worked gradually looser. The battery is really the first thing you should check - I got blinded by all the Electrickery and panicked thinking it was something more serious than it really was.

Note to self:- When you recommission the bike in spring MAKE SURE THE BATTERY TERMINALS ARE TIGHT.