Yzf 1000 thunderace rough at 3500+

[Hahadumball]

Bought as a rough runner,

Carbs completely stripped cleaned and rebuilt. Plugs changed and starts and idles fine, revved up fine in the garage. Took for a little ride and it was fine at lower throttle but about 3500rpm it was running rough and struggling to get past it no matter which gear, I gave it the beans to 3500 and changed down to try get it over 3500 and it just wasn't having it still, it did clear a little and allowed me to rev a bit higher briefly but then went back to running rough.

Could this be the exup valve? If so how do I test it to see if its working?
____________________
Fin: no matter how much I look at It I can't understand what was going through my head, all I remember is going about 80 and redlining it to stop it seizing.
360 Deg... Five 1/4 turns. :- Teflon-Mike 18 Jan 2015

[stinkwheel]

Is it getting fuel? Blocked filter, blocked tap, dodgy fuel pump?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Nobby the Bastard]

Take the cover off the exup valve, see if it moves when you rev it up.

it would normally rev higher even if the valve is stuck in the 'low rev' position. Not sure whaty it would be like if stuck in the 'high rev' position.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Hahadumball]

[Robby]

Exup valve should be one of those things that has a minor impact on performance, but not make it unrideable. Still worth making sure it's moving.

This is one of those rare occasions where I do think about a carb problem. From memory it's from right at the end of the carb era before moving over to FI, so they're probably quite complex.

If it revs up fine with no load, it eliminates some of the issues around spark - but not all. It's harder to make a spark in a full cylinder, so weak coils, knackered plugs or HT leads could be a factor, but not my first thought.

You're making power and it works up to around 3000rpm. On a bike like this, I assume that translates to small throttle openings and low power levels. So you're using the slow running jets in the carbs, and a little bit of the needle for fuel control. As you open the throttle more it raises the needle, and fails to make clean power. Filthy emulsion tubes would cause this problem, as would worn/bent/wrong needles.

Could also be blocked filters behind the needle valves, allowing some fuel into the carbs, but not enough. If that was the case I would expect it to run well for about half a mile, then shit afterwards.

But just to make it all worse, it's a 20+ year old bike with a rough running problem. It could be in the carbs, it could be fuel flow before the carbs, it could be a problem in the ignition components, it could be a poor earth connection, it could be water in the carbs. Many possibilities, half of them involving rust.

[Nobby the Bastard]

Actually I've just worked out thats.about where my fzr stopped when the valve.was stuck in the low position.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[to v or not to v]

[Fizzer Thou]

[Nobby the Bastard]

Well, I did recant that further down the thread.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050