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General Category >> Rubber Side Down! >> Throttle response oddity at 1/4 throttle
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Message started by voldigicam on 09/03/09 at 07:06:55

Title: Throttle response oddity at 1/4 throttle
Post by voldigicam on 09/03/09 at 07:06:55

Seems to be working fine except right at 1/4 throttle. Rolling on throttle I get a little flat spot there, sort of. Since I ride at 1/4 throttle lots, I stay there sometimes, then I get just a bit of irregular running, not quite surging, not as obvious as hunting.

The flat spot suggests rich.

The irregularity suggests lean.

Which circuit might this be? Suggestions?

Title: Re: Throttle response oddity at 1/4 throttle
Post by dmike on 09/03/09 at 07:39:21

I have the same problem too. After taking it to Suzuki it didn't change either. I have to check my cam pulley as I thought that was the problem. I recently got an oil leak too. Fun times.

Do you have the wheel of fortune sound? I'm not sure if what I am hearing is that sound or not, but I was hoping after fixing that the "slight bucking" as I will call it, will stop. Your descriptions are better, but that is what I think in my head when it happens.

Title: Re: Throttle response oddity at 1/4 throttle
Post by verslagen1 on 09/03/09 at 07:50:11

Volly, try the white spacer mod.

d, wheel of fortune sound? check the torque on the drive pulley.

Title: Re: Throttle response oddity at 1/4 throttle
Post by voldigicam on 09/03/09 at 08:01:09

more or less spacer? I have about 50% spacer at the moment. I'm tired of working on the thing, but I can go in again.

Title: Re: Throttle response oddity at 1/4 throttle
Post by srinath on 09/03/09 at 08:08:41

1/4 throttle is where the needle starts.
Just under that is float level.
I'd try checking float level, and then if that is right (and the gasket face is the right level +/- 1 mm) then I would richen it on the needle.

Flat spot doesn't neccesarily mean rich. Irrerugalirity is too vague to define in this context. My bet is that you are a shade rich on the float, and a shade lean on the needle, and settig the float will point out the needle as the culprit.

Cool.
Srinath.

Title: Re: Throttle response oddity at 1/4 throttle
Post by Serowbot on 09/03/09 at 08:14:51

What's your current jetting?.... What mods do you have, and what's your elevation?..

Title: Re: Throttle response oddity at 1/4 throttle
Post by voldigicam on 09/03/09 at 08:25:32

Stock air filter, new and clean, Dyna exhaust. 55 / 155 / 1/2 spacer. This one was running incredibly lean - I tweeked up progressively. The performance jump from 52.5 to 55 and from 152.5 to 155 were very distinct - the exhaust pipe temperature at high cruise speed clearly dropped, too. Just now this hole in between.

I'm at 800 ft, but go up to 6000.

Title: Re: Throttle response oddity at 1/4 throttle
Post by Serowbot on 09/03/09 at 09:15:49

I doubt if you're lean with that jetting.... Have you considered a freer breathing air filter?...
at 1/4 throttle steady, you are at high vacuum... maybe it's wanting more air....

Title: Re: Throttle response oddity at 1/4 throttle
Post by voldigicam on 09/03/09 at 10:12:29

I'll pull out the filter and do a short test ride. The stock filter has a lot of area. Somehow it breathes fine at WOT and everywhere else. Why would it not breathe fine at only one moderate demand position?

Title: Re: Throttle response oddity at 1/4 throttle
Post by Serowbot on 09/03/09 at 10:57:16

LOL!... No idea really...
It's just that you seem to have enough jetting and a free flowing exhaust... so,.... I wondered what difference it would make....

Mine has a k/n filter,.. I pulled the side plate once to see what would happen,.... it ran like cr@p..... so I put it back...

But you never know....

Title: Re: Throttle response oddity at 1/4 throttle
Post by Moofed on 09/03/09 at 12:36:29

I have/had the same symptom. Weak spot in the throttle position used for cruising at around 45mph. I had a 55 pilot (w/holes) and tried going back to the stock 52.5 and it seems to have helped, though I can still feel it some. Before that I tried leaning the needle out some (~1/3 spacer => ~2/3 spacer), but that was certainly *not* a move in the right direction.

I'm wondering if the decreased back pressure exhaust is accentuating a preexisting weak spot in that low range. :-?

Title: Re: Throttle response oddity at 1/4 throttle
Post by DrunkenDwarf on 09/03/09 at 13:19:59

I don't have a magic fix, but I do agree that 1/8-1/4 throttle seems to be a naturally lean spot.

-D. Dwarf

Title: Re: Throttle response oddity at 1/4 throttle
Post by voldigicam on 09/03/09 at 13:33:45

How high is the needle then? Wish I knew. I can fix spot lean pretty easy, although I've only done it for sweetening the idle.

Title: Re: Throttle response oddity at 1/4 throttle
Post by Serowbot on 09/03/09 at 14:53:53

Vacuum should be high in that range,.. so I believe the needle should be close to bottom... very little effect...
It mostly comes into it's own, during acceleration, throttle open, low vacuum...

Title: Re: Throttle response oddity at 1/4 throttle
Post by voldigicam on 09/03/09 at 15:23:07

If that is the case, and this is a lean spot, then the fix is easy. I recall my grandfather doing it many times when I was a child. A quick pass of the file over the needle to sweeten the mix right there!

Title: Re: Throttle response oddity at 1/4 throttle
Post by Serowbot on 09/03/09 at 17:14:42

Ohh!... I think that baby is chromed.... not good for filing... :-? she'll rust up...

I think you're still mostly on the pilot at that throttle... is it possible, that you are interpreting small wind gusts or changes in air density, as surges or hesitations?...
I ask, because I've done it myself.... :-? Here in the desert, you can feel little pockets of hotter and cooler air, that must be the size of a small wading pond... come and go in a fraction of a second...