Quick carb question

[vfrman]

Ok....I think I know the answer, but I want to ask anyway.

I was having a problem with the bike revving past 7k, so I got into the carbs thinking it was running too rich. Turns out I had 120s all around. I was also running a stock filter, which was filthy. SO... I rechecked the idle screws and set them to 2 1/4 turns out. (I have a half system on the bike). Also swapped out the fronts for 118s. Finally, I cut out the filter element and replaced it with a k&n panel. I was going to shim the needle and drill out the bleed hole on the slides, but the needles are aftermarket and adjustable, and the hole was already drilled out.

So...I get it all back together and running and take it for a spin. I can get all the way to redline now but I still have a slight stutter/stumble at 7k-ish rpm. My next thought is to get back into the carbs and go one notch out on the needles (I THINK they are set in the middle of the range right now.) One notch out means more needle sticking through the jet which means less fuel...right? Also, the needles are what control midrange and main jets are top end, right?

[CMSMJ1]

Yes

Though I see it is part throttle =needles - the slides are not fully retracted

full throttle - main jets as the needles are full out of the way..

[Neosophist]

Good to hear that it is nearly sorted. Sounds like your right on the money too.

This flat spot is quite common and well talked about as you've no doubt read about in countless posts over the years.

It's usually caused by the bike being too lean in the midrange.

(As for your last question, The midrange circuit is the needle and throttle plate and slide in combo, this controls the change from the slow jet to the main jet. normally you only adjust the needle, but can change the spring / hole size in the slides too.)

Raise the needle via a shim (Rick-O sells pre-made ones), or in your case as you have adjustable needles, start by movning the clip down a notch on all the needles.

This will shorten / raise the needle. Now it will come out of the needle holder sooner, thus allowing more fuel into the engine and hopefully smooth out the lean spot.

It's usually always caused by the bike being too lean in this area, so lowering the clip / raising the needles should be the way to go.

[vfrman]

So you think it is too lean?

[Neosophist]

So you think it is too lean?

I'd say its too lean at that point. All of them i've seen have been lean there. (transition) which is why you get the flat spot. You'll soon know if its too lean by changing the needles, should help it.

[vfrman]

I'll give that a go tomorrow....maybe. LOL.

[vfrman]

OK, on your advice I went one notch down on the needles to bring them out of the jets more. I took the bike for a quick run around the block a couple times and it was running much better. I had it stumble just once at around 12k. Kind of odd. I was at WOT so maybe the fuel tap was restricting fuel. Hard to tell. I might just get it on a dyno now for the fine tuning. I pulled the rear plug before messing with the carbs, and this is what it looked like.



I also pulled it after the tuning and it pretty much looked the same. If anything, it might still be a tad lean....

[Neosophist]

They look good to me!

I think you could get away with running 120's all around but depends on if you want to go through the hassle of faffing around changing jets.

Doubt your peak power will change but it might feel a little crisper if its slightly lean at the top end, dyno run will tell you more though.

[vfrman]

Ironically there were 120s all around to begin with. I wonder what would happen with a 120/122 setup. I just need to get it on a Dyno now.