Yamaha XJR 400 carburettor issues - Update!

Leodbroga · Renault 5 Driver Joined: 13 Mar 2012 Karma :

Hey, got myself my first big bike almost two weeks ago, a Yamaha XJR 400 and guess what? It's giving me jip. Bear with me here, because it's pretty confusing.

When I got the bike, it wouldn't idle properly; either at 2.5K - 3k revs or just below 1k, now this problem has been partially solved by getting the carbs balanced today. It now idles around 1.5k revs, which is perfect.

But my issue is that once warm, the revs get 'stuck' at around 2.5K still, so at lights and junctions it's a nightmare to do a smooth pull away. It may sound trivial but I know it isn't right, and to make it even more confusing if I slightly let the clutch out and labour the engine, it can sometimes return to normal idle.

Now, I've asked a few mates, and I think it's either the clutch, which is also very rumble-y and I suppose worn... Or it's the throttle cable getting stuck. I can't see how it would be the carbs seeing as they've been taken apart and were not dirty and are in balance.

So, denizens of BCF, any suggestions? I'm at a loss here.
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Yamaha SR125; Yamaha XJR 400; Suzuki GS500E

Rob W · World Chat Champion Joined: 09 Nov 2004 Karma :

You may well have an air leak somewhere. Were the carb rubbers in good condition?
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Budgetboy · Scooby Slapper Joined: 05 Apr 2012 Karma :

Pol Anorl · Banned Joined: 13 Apr 2010 Karma :

^ both the above definately sounds like an air leak
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Leodbroga · Renault 5 Driver Joined: 13 Mar 2012 Karma :

Leodbroga · Renault 5 Driver Joined: 13 Mar 2012 Karma :

Finally got round to taking the tank off and having a look. I think I've found the culprit:

https://cdn.bikechatforums.com/files/223995_4537046545631_763409687_n.jpg

Pretty impressed I got the tank off by myself, especially considering a couple months ago a simple oil change scared me. Thanks Rob, Budgetboy and Dumball! Karma heading your way. Thumbs Up

I noticed that cylinder 2 wasn't running as hot as the other 3, and checking the spark plug it looked hardly used in comparison. Took me a while to put two and two together but obviously it's been running incredibly lean due to the massive air leak. I'm hoping this will stop my idle creep finally.

Any suggestions where I can source a new vacuum hose?
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Yamaha SR125; Yamaha XJR 400; Suzuki GS500E

_Iain_ · Banned Joined: 01 Feb 2012 Karma :

Thats not going to help matters!

Take the hose down to halfords/scrapyard/car parts place and say "i want a bit of pipe like this" and they'll sort you out.

Halfords will ask many questions, all of them irrelevant as 90% of the employees wont have a fucking clue. I genuinely facepalmed as the guy went looking for carb cleaner with all the car waxes and shit.

But basicly, fuel hose - or scrappy, anything thats connected to the intake manifold of the car will work brilliant and is likely to be the same sort of bore. Thumbs Up

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janner_10 · World Chat Champion Joined: 26 Sep 2011 Karma :

If you have the slack - just cut the last inch off. Failing that as Iain said try a breakers, as long as its in good condition and the same ID you can cut to suit, it doesn't have to come from a bike.
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chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Measure the OD and ID and look on ebay Thumbs Up

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ZaphodBeeble · World Chat Champion Joined: 10 Feb 2004 Karma :

That's possibly just a breather for the float bowls. Unlikely to affect the idle if it is.

It's likely that you have worn throttle valve shafts, I've seen this before on an XJR400. They can allow air in and will make it hard to balance the throttles.

EDIT: I'm going blind I think, I can clearly see the bloody vacuum nipple now.
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