I have the judders

pinkyfloyd · Super Spammer Joined: 20 Jul 2010 Karma :

OK Clever mechanical people of BCF I need a diagnosis.

I have a 2013 XJ6N, fuel injected. Between 1 and 4K revs the engine stutters, judders, is a little jerky to ride and occasionally (quite often) backfires. Only happens when it has warmed up and goes away after 4K revs but that means to ride the thing I am riding around at 30mph in second gear as 3rd causes the judders because the revs have dropped.

It has been into a mechanic who changed the spark plugs, this seemed to fix the issue for a while but now it is back with its friends and worse.

What could be causing this? A brief search suggests a blocked jet, would Redex do any harm or indeed any good?

Thanks.
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Water in fuel?

Have a look for water droplets in the bottom of the tank and in the fuel filter with a torch.

Also have a look up around the area of the coils and HT leads in a dark shed for evidence of arcing.
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bugeye_bob · World Chat Champion Joined: 05 Sep 2013 Karma :

Did the mechanic say anything about the plugs when they changed them, sooty or anything ?
may point towards it running rich, does it feel like it is on choke even when warm ? on cars that points towards a CTS issue, which makes them run rich all the time.

pinkyfloyd · Super Spammer Joined: 20 Jul 2010 Karma :

Matt B · World Chat Champion Joined: 01 May 2012 Karma :

How many miles have you done now? Have the throttle bodies been synced ever?
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pinkyfloyd · Super Spammer Joined: 20 Jul 2010 Karma :

orac · World Chat Champion Joined: 25 Sep 2011 Karma :

could be an air leak on the intake side too, warm it up spray something like WD40 around the intakes, if the RPMs change you found your problem
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Fizzer Thou · World Chat Champion Joined: 06 Aug 2011 Karma :

A friend had a similar problem on their injected bike.The initial thought was that it was the throttle position sensor but in the end,although the TPS adjustment did make a slight difference,it was the fuel filter that needed replacing Clapping

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pinkyfloyd · Super Spammer Joined: 20 Jul 2010 Karma :

Howling TerrorOutOfOffice · Super Spammer Joined: 05 Dec 2008 Karma :

It shouldn't be costly.
Drain tank.
Remove tank.
Unscrew the retaining bolts and take care not to damage the large O ring.
Extract what you need to get to the filter and replace it.
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