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Misfiring Problem '04

Dave 321

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Hi guys,

My bike started misfiring intermittently about a week and a half ago after a particularly cold and wet ride into work. It was fine in the morning and then when I started the bike up to get home from work it was only firing on three cylinders - I believe it is cyl #4 that isn't firing properly, checked the manifold with my wet finger. On the monday afternoon when it started it was really bad, I could barely give the bike any throttle without it misfiring but it cleared up somewhat by the time I had gotten home (I have a 45 mile ride each way to work and back) but never really got any better from that point onwards.

On the saturday, having ridden my bike to work with the problem on going I gave my bike to my local yamaha dealer and basically gave them £230 to change my sparkplugs and balance my throttle bodies. :mad: They also said my air filter was not seated correctly which I'm pretty sure was bollocks because I had only just put the air filter in a week beforehand.

After getting my bike back, they problem seemed like it had disappeared, but I don't think I gave it a thorough enough test ride. The bike still misfires sometimes, but not as often as before.

Basically, sometimes the bike misfires on idle or when I throttle it hard but if I'm doing ~70mph (6th gear ~6k revs) on the motorway I can give it full throttle and it'll just pickup nice and steady. It's particularly bad at low revs (sub 3k). Sometimes I can ease into a full throttle position and it might be OK. Also, the problem does not seem to correlate to engine temperature.

2004 model
55k miles (been absolutely fine with no problems up to this point)
TPS replaced about a year ago

I rang up yamaha straight away after my ride to work following them playing with my bike to book it in again for this coming friday. Believe it or not, the tech said to me that it's probably just that the air filter has become unseated again!

Any help will be appreciated guys!

Dave
 
As you know from changing the air filter yourself that it sits in a very snug groove in the airbox and cant become "unseated".

It sounds like you may have a loose or damaged intake manifold joint. Check the parts shown in the RED box in the .PDF attached. When it's misfiring at idle shoot a spray of WD40 at the boot and see if the revs pick up. If so, you have found the problem.
 
Thanks John (I assume that's your name?)

I'll give that a try when I get a chance. Theoretically, if that is the problem then when I spray WD40 onto that area it shouldn't matter at the time whether it's misfiring or not - The fuel mix will be affected regardless, correct?
 
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