jetting sensitivity

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#1
Wow! This Kdx 200 jetting stuff is way more sensitive to temperature than I could have imagined. You may recall that that it seemed odd that my bike was starting on the first kick without the choke. Well, that was in 85 deg. at sea level with high humidity. You'd think it would run way rich, but seat of the pants feel and pretty plug said otherwise. This weekend we got our first cold blast---55 deg.---what a change. Took three or four kicks with the choke to come to life and then would never settle down to idle. Had to back the idle screw down and adjust the A/S. Only now have I witnessed throttle response right from idle in each gear---it's scary--- front end comes right up with a snap of the throttle. Question---setup 1990 kdx 200---pwk 35, 38 pilot, 52 main, cel 2nd clip---All thought this jetting was too lean, but perhaps the float level at 17-18mm richens the whole circuit---should I go leaner still on the pilot to get this response at 85 deg. ????
CC, Wibby,CDave????
 
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#2
There is as temp/el. chart on CDave's site that will give you an idea of changes needed.

I don't follow your question. Certainly the cooler temps cause your bike to run effectively 'leaner' with the same jetset (cooler temps require richer jetting). To jet effectively 'the same' at a higher temp, you need a corresponding leaner jetset.

Keep in mind that it's never going to be 'the same.' Ex: While you can 'properly' jet for a 12,000'el. ride, your bike will still run 'fer crap cuz thar' ain't no air up there!

Likewise with temp changes to some extent. There is more air in a given volume of cool air than in hot air (RH or relative humidity changes notwithstanding).

THAT said, cool air is commonly (not always) drier than warm air.

A 10-15º temp drop during a ride can have a considerable effect on my bike.

......and you're talking 30º!
 
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#3
Thanks for the feedback, CC. Meant 152 main. I was shocked to note such a huge difference in performance. In the 70's, my old Suzuki 185 seemed to run pretty much the same all the time---however there was a little more pep when things were cooler. I guess the question is why I might want to run a 35 pilot at 85 deg.--- from everything I see i'm already jettted too lean from the get go??
 
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#4
Yeah...35 on the pilot does seem lean 'compared to...'. If your bike is mechanically ok, and that's what it takes.....well, that's what it takes.

re: 'and then would never settle down to idle..'

A runaway idle (I do see that the resolution for you involved turning the idle speed down....that's not the issue) is a sign of a too-lean pilot. The bike may well RUN fine when it's hot, but the too-high idle part is an indication that you're on the lean side.

Don't discount the air screw. It gets overlooked way too many times, seems to me. If you 'set it and forget it', you likely are making a mistake. Although...it's been awhile since I fiddled with an oem carb, and one of ron's mods is a pilot circuit finesse job..I do recall that relatively fine adjustments in the oem keihin made significant differences. I'm saying maybe keep the 38 pilot for higher temps and use the air screw to adjust for better throttle response.

Whatever works! ;)
 
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#5
I must reply. If for no other reason that to disagree with CC,(for a change). Ok. Here is my take, for what its worth.
When the weather is warm and the bike is cold, it takes a a/f mixture that is
leaner than when the weather is cold. Cold air means more oxygen thus leaning the a/f mixture whitch is why your bike is harder to start in the cold,
because more fuel is needed to compensate. So, the runaway idle is caused
when the air is cold because your a/f is closer to what your bike wants. The high idle goes down when the bike is warm because the a/f is now richer than
it needs. This situation to me says your pilot is still a little rich.I do not think
a 35 pilot is out of the question. May be even a 33.
BUT... heres the big catch. Jet your bike to run good warm!! Who cares
what it runs like cold. You dont ride a cold bike,, well for more than 2 min. or
so.(Its warm by then).
I run a 35 pilot and would try a 33 if i had one. The low speed 4 stoking
does not bother me enough to buy a jet.

So, in summary, when you start a cold bike in the cold , and it has a runnaway idle but slows to normal as the engine warms, that tells me the pilot is to big. Remember though, jet for how the bike runs , not how it starts.

Steve
 
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#6
Steve, The idle wouldn't come down after about 5 min. so I had to back down the idle screw. Once the idle was REAL slow started tinkering with the A/S and found max rpm at 2.25-2.5 turns out. Probably means I need to back down pilot to 35 when the temps. up! Any input is appreciated.
Old-N-Notslow
 
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#7
I don't read anything O&S said as contrary to what I said. :think:

Note the runaway idle I'm referring to is with the idle adjustment out of the picture (the screw not even touching the slide). Having said, 'on the lean side' isn't necessarily saying to jet richer...just which part of a 'range' you're in.

re: 'may well RUN fine when it's hot..' I said that. That's where the paste came from. ;)

Oh well......listing point by point isn't productive.

BTW, a max rpm air screw adjustment most likely is not where the bike will have the best throttle response.
 
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#8
CC said: BTW, a max rpm air screw adjustment most likely is not where the bike will have the best throttle response. That is very true---I think the best response was out 1.25 turns. The 2.25-2.5 turns out was strictly for checking the mixture on the pilot circuit.
 
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#9
Cicone,
I think you are going in the right direction. Try a leaner pilot and tell us what you think.
CC,
I took your post to mean that a high idle when cold was caused by too lean
a pilot. I feel it is caused when your pilot size is getting closer but still
a little rich. Everyone seems to get it as they lean there pilot, so maybe thats what you mean, or maybe I just dont get what your saying(more likely).

P.s. Cicone, where do you ride as I am in fla also.
Steve
 
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#10
Old-N-Slow---I've got to subscribe to this list. Try to PM me at jay.cicone@raymondjames.com.
 
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#11
re: 'I feel it is caused when your pilot size is getting closer...'

Pretty much. Certainly the way it runs hot is what you're (we're?) after.

My bike doesn't run fer diddle when it's cold...lean bogs, no response a'tall. Heck..I can let the thing sit there for 10 minutes 'warming up' before it's 1/2way good to go (rarely a plug loading problem even in that situation).

When it's hot? It's a different animal.

So, I have to sit and let it cool off so it runs like crap again!
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...just kidding. ;)