My dear Divvy , since when I got her last year , has always had a very noticeable flat spot between 2500 and 3000 rpm, and right now it's the only thing I haven't been able to get resolved.
Before I thought it was because of the timing chain which did need replacing, but now that it has been replaced, the flat spot is still there, unchanged.
I have synced the carbs and tuned the idle with the mixture screws , using the "thermometer on the headers method" as described in this forum.
Idle is now practically perfect but the flat spot is still there.
Let me describe it the best I can:
Bike pulls very well even in 6th gear at "almost idle speeds" ( around 1500rpm ); if I open the throttle she accelerates fine, reaches 2500k , acceleration slows down to a crawl and intake sound changes and becomes "throaty" ( very low frequency and louder ) .
Even if I open the throttle more the bike doesn't accelerate more.
The problem is waaay more noticeable if I'm going uphill.
As soon as the rpms hit 3000k the sound returns normal and the acceleration becomes strong again and keeps on with no further problems, only some vibrations (which I know are typical of the model) from about 3800 on to 4500 and then starts screaming like a banshee from 6000 and pulls like mad up to redline.
This is a problem if I need to quickly change speed 'cause I need to shift down one or two gears to avoid this flat spot.
Bike is a 1998 european Diversion, stock airbox, stock air filter , stock exhaust.
I've read on other threads that the 2500-3000 band is when the carbs switch from the pilot jet circuit to the main jet circuit and was wondering if there is something I can attempt to change o re-tune to clear this flat spot; I've read that swapping in some #20 pilot jet does improve low end , but also that this seems to be a mod that's valid only for US XJ600 bikes since european ones have different carb settings and jets.
Has anyone had this issue?
Thank you in advance.
Michele