rpm and trottle operation question.

[di_]

Hello peolple )))
I`ve got little odd rpm`s
When I operate trottle rapidly everything works quite good - rpm`s increases as it should be.
But if I open throttle very slowly I see that the rpm falls down on 100-300 for the moment before rising.

Why it does so? Is that normal?

Buy the way, accroding tech manual I have to check valve clearance (more than 18 000km passed)
So, if that a reason of such behavior? Maybe it`s time to tweak valves or what ?

 

[Lou Wambsganss]

I notice the same thing when my engine is cold. I think it's just a result of the OEM fuel mapping being fairly lean (like most modern bikes) to meet emissions standards. The off-idle transition is one of the hardest operations to make smooth, even in old carbureted bikes. Now that I have a much longer commute, I've been strongly considering investing the $300 in the Bazzaz tuner just to smooth out the idle transition.

As far as valves, they should be checked just to be sure, but I doubt it is causing the noted behavior. Most members (including myself) report the valves mostly wear tight for the first couple of valve checks. This is due to the valves and seats lapping into each other. Once they settle in after a couple of checks, they should be fine for quite a while with normal maintenance.

 

[di_]

Yep. agree! This thing more obviuos in cold engine - I even got stalled copule times after such smooth trotlle opening.

 

[L.B.S.]

I've had one or two bikes over the years that had a similar thing but instead of idle, it was at full throttle. They didn't feel like they were running as good as they could, but if you backed off ever so slightly, the speed and rpm's actually increased. They went faster at 7/8ths throttle instead of full throttle. Ended up being a lean condition, and although they were with carbs and main jets instead of EFI and idle or pilots, showed the same effect; running too lean for the condition.

My buddy with a Yamaha Super Tenere is having a fueling problem too. A bit of off idle stumble, and some larger throttle opening hiccups at highway speed. He is going to be getting a Power Commander in the next week or so to try some different fuel maps and see what that does.

Good luck di, and let us know how it goes as you try and track it down!

 

[Deleted member 1183]

Same here, only manifests itself on a cold motor. Fuelling more or less fine when fully heated.