Hi,
I have a similar problem to raptor2210's previous post with the same subject name.

"the bike seems to 'get stuck' at around 6000rpm. This is quite difficult to explain but here goes: for example, if I was to let the revs drop to around 5000rpm for a bit then open the throttle the revs will rise to around 6000rpm then they will stick there for a while and the bike makes an almost hollow roar that I would describe as intake noise. The only way to get through it is to either ride it out (eventually pulls through after a few seconds) or slip the clutch."

I cleaned out the carbs, had them balanced, changed the fuel filter/sparks/oil filter and other basic things. I also took the cover plate off the exup valve and manually turned it with the engine running (sounds much louder in one direction than the other) which convinced me that the valve wasn't seised, watched the servo move the cables/pulley under the cover plate when the run switch is turned on.

After doing all of this there was a marked improvement but after doing 10-15 miles the problem started to return.
If I'm doing 30mph for a while then give it some, the revs get stuck for a few seconds with the hollow roar sound. It dosen't always happen but it still makes the bike pretty twitchy in traffic.

In raptors post it was apparantly the exup at fault but mine 'appears' to be ok.
Could it be an electrical thing in the way the exup is controlled or perhaps something else?
Thanks for your time.

I might not be right but have you checked the battery. If its on its way out it plays really funny games.

well, the battery was the first thing I changed (for a new one) before I did the other work on the bike.
I had to leave the bike for a couple of months whilst away with work and when I came back it was completely flat but it seems to have held charge ok since then and so I haven't really considered it since.

I should also stress that on this last test ride, from cold the bike seemed to pull great, it was only after the bike was warm and stuck in slow traffic that the problem came back.

Also the valve clearances were done so that can be ruled out.

I'd have said the exup.
Have you adjusted the cables ? If so did you do them up finger tight only ? Are the cables in good condition or is there any evidence of fraying ?

Have you changed the spark plugs recently

I had something very similar to this on my 3JT but at 10-11K (it would continue to rise very slowly to the redline) and it turned out to be the coils breaking down. They are more highly stressed under load then at idle, so even though you can see a spark when turning the engine over, that does not mean there is a good spark at high revs/high load.

thanks for your replies,
plugs were changed recently, exup cables appear ok, no fraying and yes they are finger tight.
never dealt with coils before. how do i go about testing/fixing them?
is it the boxes that the spark leads plug in to?

I don't think that the EXUP valve will cause the symptoms you are having.

I think it is more likely either faulty HT leads or one or both of the coil packs are on the way out.

ok, what coils would work? does it have to be 3tj specific or can I look at a cheaper option?

hi there try swoping cdi box with a mate coils 2 if pos one more check fuel cap breather u can do that by running fuel off into container 2 ltr thould run through in no time at all if it petters out youv got it !!