Dead spot at 6000 RPM

Hi guys, had an XJ700X for a couple of months now and I wanted to ask if everyone feels like me that there is a dead spot in the torque curve around 6000 RPM. This is where I spend most of my highway miles at and it sucks that I don't get a good pull at this RPM range, 5000-7000. Bike pulls well below 5000 RPM in lower gears and pulls great above 7500 in any gear but it just feels like in the mid range it is a little gutless. It was like that before I went airpods/reset and after so it must be a design issue for this motor I think. But is it the cams, overall engine design or something else?

 

That is going to be something specific to yours. My X is good below 4k, pretty damn good to 7k, and then screams till it hits 9k which is when i shift, at least that was before I tore the carbs apart to finally get around to replacing throttle shaft seals . I would get a spark plug socket, go find somewhere desolate, cruise at 6k rpm where you think the dead spot is, then pull the clutch and shut the bike off. Once you stop check the plugs and see if they look odd. Also, when it was pods, did you check the type of jets and needle? Anything not stock may give you a dead spot, and the same goes for airfilter/intakeboots/ect.

 

Which ignition module do you have?

 

What you've described is typical of CV carbs running without the airbox, doesn't matter what bike we're talking about.
The airbox has little effect below 5,000 rpm. After that it slightly restricts the flow and helps raise the throttle slides.
Consider it like a power vacuum assist for your slides.
When you eliminate this restriction the slides no longer open smoothly above 5,000.
This can be improved by experimenting with softer slide springs, easiest solution is to put the airbox back.
Many go blue in the face trying different jetting.
I have dyno prints of my 750-X running OEM jetting but no airbox. Great to 5,000, then huge dip in torque as you've experienced then by about 6,500 the slides overcome the springs and it runs to redline.
go here https://xjbikes.com/forums/threads/highly-modded-650-seca.85760/page-2

What condition was it in when you started riding it? It's possible there was another issue at the time affecting the midrange response.

 

The flat spot was worse with the airbox and before I went to pod filters and rejeted. So that's not it.

 

The bike is in excellent condition with 20k miles on it, imported from US to Europe. Engine sounds great overall. To clarify, the bike is not sputtering or popping in the middle range, it just feels like not puling hard like it does in the lower or higher RPM.

 

The ignition in my bike is all stock except for new spark plugs, and I replaced the coils with cheapo Chinese ones from amazon. Here is the link to them if you are interested. https://www.amazon.com/External-Ignition-Yamaha-Silverado-5VN-82310-20-00/dp/B08F7VWDZM. Just to make sure, but the bike right now is stock? It has the stock airbox and everything?

 

Quick update: having installed pod filters and short loud mufflers, I went with Mikuni size 40 pilot jets and 115 main jets. Bike is very lively. Gone is the weak spot around 2000 RPM, bike revs nicely from 1500 rpm onwards. There still seems to be a slightly dead spot around 5-6000 RPM but it is less noticeable.
Overall, great success!

 

Also shimmied the needle.

 

Latest modification I did is shortening the needle spring by tying together the first three rungs with some thin wires. Seems like it worked well in boosting mid-throttle response in low and mid RPM range.

 

Replaced the TID 14-35 with a TID14-49 CDI from a YAMAHA FZ 750 1985. Feels more peppy.