rough running at very low rpm/ throttle opening

[pitternator]

well I suppose it had to happen at some point !...but my faithful fazer has developed a fault after 5 yrs and 30k miles of my ownership. The first one mind.
Basically I just noticed a blub blub blub type noise up to 3k rpm at small throttle openings. Like  a misfire but no backfires, so it seems like a fuelling issue to me. Once over 3k rpm the bike runs fine, and mpg seems Ok too. So I dont think its  a main jet issue. I suspect a blocked pilot jet in one carb. Never having touched the carbs I am hesitant to mess about. But does anyone know how easy it is to remove the jets to clean ? I suspect Mike will know in a flash.Is this something I should contemplate doing myself or best to book in to a dealer ??

I hope its nothing more serious than this.

[Falcon 269]

Hi Jon

Any carb jet work requires them to be removed so if you're not happy about doing that, no point in proceeding any further down the DIY route.

Has the bike been standing unridden for any length of time?  Have you recently filled with fuel?  I'm thinking maybe water in the fuel is one possibility.  You could drain each float bowl to see if there's any cack inside but be really careful not to overtighten the drain screws when you refit them ... easy to crack the float bowl and they're not a separate spares item, so you can't buy a single replacement from Yamaha.

Another possible is a leaky float needle seat O-ring.  A small leak past one of those would cause the float bowl to fill too high, in turn making the fuelling over-rich at part throttle openings.  Rectification is a carbs-out job again.

Having eliminated water in the fuel, I'd try running some fuel cleaner through the next tank or two of fuel before delving into carb work.  If the problem persists, dealer time ...

... however, before fixating on this being a fuelling issue, I strongly advise you to check the plugs and plug caps first.  So many odd misfires/hesitations present like a carb fault but are actually down to the plugs.

Mike

[pitternator]

Hi Mike
thanks for the advice. Yes the bike hasnt been running that much this year , but has had some long rides, and plenty of full throttle .I was more concerned about a flat battery than carb issues...but cheap fuel is a problem at the moment ...the GS dont really like 95 octane unleaded...put 98 in and it goes really well, 95 not so good..
I too am also suspicious of plugs as they are due for renewal. But the bike does rev hard and cleanly over 3k rpm with no stutters or roughness. I am thinking of getting a dealer service as the brake fluid is also due for replacement . I just wanted to know if cleaning the jets was a job I could possibly do...but I will stick to just draining float bowls and some carb cleaner for now. I go on tour on the GS in just 3 weeks time, so dont have designs on servicing the fazer just now. It can wait till I get back I think.
Thanks.

Jon

[mikelockyer]

Hi It sounds as though this all could be solved with a good service by a competent yamaha mechanic. Sometimes you just have to cough up the cash.

[Falcon 269]

The fact that it revs out fine at full throttle and pulls clean above 3k rpm doesn't necessarily mean that it's not the plugs, Jon. 

New plugs, fuel cleaner additive and some regular running should do the trick.  Park up that Bavarian farm vehicle and ride a proper bike, mate ... :lol

[tomlinscote]

+1 for the plugs, I had a similar problem, rough below 3k and normal above that, changed the plugs and made sure the caps were in good nick and DRY and pushed very fully home and then no probs normal serve was resumed

Tommo
Tried the new GS liquid cooled and its great!

[gowerclub]

Yep - had exactly the same symptoms - new plugs - goes better than ever..............

[pitternator]

Thanks chaps!
Ref the " bavarian tank"...PMSL ...good one !..tbh some days its very apt.. :eek

Just typically , when I fired up the fazer , it didnt do it ! But new plugs are a definite job now.How awkward is it to get at them...never having had to do the job in all my years of fazer ownership !  :o

[Dave48]

With the "Yamaha" plug spanner supplied in tool roll-easy enough.....Without....... :'(

[red98]

:agree ....yep...thats the tool for the job