Proper throttle response???

wanaride

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#1
I've worked on the jetting of my new 200 for about two months and I'm still confused as what I should expect for "proper" throttle response. (I have used the search function on this site, read CDave's carb tuning tutorial, and am NOT running stock jetting; Main=155, pilot=42, needle 2nd clip from top, AS=1TO, airbox snorkel removed, 32:1 H1R, stock pipe & silencer)

Let's say the bike is completely warmed up. I'm lugging around the yard easily in second gear (flat riding area) with no real engine loading other than my girth...and then I twist the throttle open.

If the jetting is properly dialed in, will there be any hesitation or "bog" at all, or will the engine start screaming up in rpm?

Thanks for helping me out!
 

CaptainObvious

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#2
The bike should "jump" when the throttle is wacked open. If it falls on its face you're too lean on the pilot, a/s or, less likely, the needle. If you get a bike baaaaawaaaaaaa you are too rich on those same circuits.
 
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#5
Maybe a defiinition of 'instantaneous'?

There is a 'hesitation' you could reasonably expect that keeps a small motor that has traction from hitting 6kRPM. More likely the back end with break loose, which will make that 'hesitation' considerably less.

How about this? Consider you have your stereo running at a fairly high volume, but the speaker switch is 'off'. Turn the speaker switch 'on' (well to a postion that selects an installed set of speakers?).

How fast do you hear noise (or blow up your stereo ;) )?

Not 'instantaneous' I guess, meaning not exactly at the same time you hit the switch....but close enough to it that there isn't a whole lot of realtive argument to the contrary.

Depends on speed, too. From .5mph, a flick to 1/2 throttle in second/third gear isn't likely to be too amazing.

From your description of the situation, I'd expect the bike to be pretty much happening now when you wick-it open.
 

wanaride

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#6
Nope on the wheelie. When I'm charging hard and shift into third on level ground, the front wheel will come up, but when I'm lugging around the yard in second gear (maybe 5-10mph) and open the throttle quickly, no wheel loft.

When I have some speed (on an open trail) and I open the throttle, the response is pretty quick, but there is definitely some hesitation when lugging around the yard. Maybe it is a loading thing instead of a jetting thing...
 
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#7
There is quite a difference between the two (plug loading and carburetion).

If your plug is loading up (due to whatever reason....wrong plug, bad plug, weak ignition, bad fuel, too much fuel, etc) the bike will misfire when you crack the throttle. 'Misfire' in this case meaning it won't fire. Surprisingly, this state of affairs seems to be often confused with over-rich carburetion.

Not exactly.

Maybe the plug loaded up in the first place due to too much fuel, but the burbling, misfiring mess you get as a result is due to ignition failure. The bike in that case is 4-stroking...firing every other time like a 4-stroke does, not every time ('time' being a TDC ..top-dead-center..event).

IF you are experiencing plug loading due to excessive fuel it is more likely a needle problem than it is a pilot circuit problem. Well, unless your pilot circuit is way off.

All of the carb circuits work together and thus overlap quite a bit. A too-far off main can effect the idle circuit and thus off-idle throttle response. Trying to resolve such a jetting situation by turning the air screw is a waste of time.

If your bike is jetted fairly correctly, there will be no plug loading problems from carburetion. Out of the box, the kdx will indeed have loading tbls in most situations.

.....which is why rejetting is such a large benefit.

You might try a different plug. A BR8EG is a good choice. Any new plug...even a standard fat electrode/nickel ES plug will run better for a little while.

See if that clears up the hesitation you are experiencing.

You should have none, nada, zero, zip hesitation in the situation you describe.
 
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#8
My experiance when I have the carb set right:
At a slow crawl in 2nd gear, almost stalled and bike wobbly, no clutch; I wick the throttle and the front wheel instantly leaves the ground without using any body language to help it up. I notice this because it looks cool to do a wheelie up to maybe 25mph with the front wheel not turning at all. I do this on pavement becuause then I don't get rear wheel spin.
The most important adjustment in my opinion for this test is the A/S. I will play with the airscrew at 1/8 turn at a time and can definately tell a difference in performance with just that little amout of adjustment. This setting is very sensitive to atmospheric conditions and I find that I might need to touch it up as the day heats up or the elevation changes. I keep a small screwdriver tucked into my boot for a quick 1/8 to 1/4 turn during the day. Once you get it set right, you will know what to look for and what direction to make your adjustment. Keep working with it and don't give up until you understand what affects your performance.
 
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#9
Preach on brother!!

Can I get a AMEN!


This has been harped on considerably.....cuz it's important.

The air screw is indeed a significant (putting it mildly) piece of the puzzle. It's likely more of an issue on a modified carb (as from rb-designs).

I do it a bit differently, though: ;)
  • I carry my screwdriver in my crossbar pad
  • I've found 1/16 turn to make huge differences

Certainly it is something that I change often during a single ride depending on elevation, temps and the type of response I'm after. It takes just a bit of a tweak to the air screw to reduce front wheel pop-up in nastier stuff, or put it back in if I want to be picking the front end up on a regular basis.

It is indeed a fine tuning device. Take that either way you want.

Oh..keep in mind that an air screw adjustment will likely NOT be fully evident immediately. Don't adjust it, blip the throttle once in 2nd gear over a 10' distance, decide you need to adjust it some more. Run it for 30 seconds or so to get the carb settled on your new setting before you change it again.

Once you know how it responds, you can dial it in as easily as setting your microwave to an exact 'seconds' setting to perfectly reheat that warm, very warm, cool or plain cold cuppa.
 
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CaptainObvious

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#11
AMEN Brothers, Amen.

CC, good idea on the cross bar pad. I knew it was there for a reason.
 
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#12
For some reason I don't like using the crossbar pad......Oh yea, Kawadougie keeps reaching over and taking it for his own use when I'm not looking! At least in my boot, he has to ask, and if he is riding too fast for me, I won't loan it to him!
 
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#13
One of the good reasons to keep it in the pad is that you get to buy a new screwdriver a few times a year.....after it's fallen out....again.

But I keep a spare in my fender bag!
 

wanaride

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#14
First, many thanks to everyone who takes the time to help out newbies like me! :worship:

I must not be "there" with the jetting. I tried learning wheelies this weekend and there was NO WAY I could loft the wheel in 2nd gear while my butt was on the seat. When I stood up AND compressed/released the front suspension AND jerked up on the handlebars AND rolled the throttle, YES, the front wheel would loft in that situation. Of course, now my arms and back are sore...

I WISH I could get the performance skipro3 is talking about. Is 200lbs too fat for this kind of performance??? :laugh:

Main = 155, Pilot = 42, Needle = stock and in 2nd clip from top, Air screw = 1 turn out, airbox snorkle removed...I guess the jetting needs more work.
 
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#15
Keep playing with it wanaride. Sounds like you could go leaner in all the circuits, but start with the WOT and get the main right. Work from there. Do a search on jetting if dare, there is a ton of info here at DRN on the subject. Buy lots of plugs and a fresh hacksaw blade and a couple of jets. Use only fresh gas and oil mix, or better yet, use a race gas. The race gas won't give you any performance enhancement, but it will provide a fuel that will not change your jetting charactoristices between tank fulls. I use VP C-12 becuase it was recommended and it works for me. The fact that you want to improve performance and are willing to research it, tells me that you will succeed. BTW I am 180 butt neked so 200 is not too fat by any means. You will however, start looking to improve your suspension once you got the jetting right.