MO' Jetting

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#1
At the risk of being berated, threatened and thrashed, I have a jetting question. I'm not sure how I would have searced for this thread, so here goes:
96 KDX200 with milled cylinder, FMF Turbine Core 2 silencer, 50/50 race fuel mix, and riding at 1500-3500 ft elevation. I bought the bike this way last week. I just drilled the airbox lid like Swiss Cheese, and added an FMF Gnarly Woods pipe. What would be a good jetting set-up to start the tuning?
 

canyncarvr

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#2
Bad risk! ;)

Having no idea what 'milled' means....having no idea what '50/50' means, anyone that tells you they know what you need is mostly likely wrong. They would be right only if they guessed correctly.

AND if you followed any such recommendation, you would be making a mistake.

Follow the info on CDave's site (no search required). Start rich, do the jetting checks and head toward lean one step at a time.
 

fuzzy

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#3
2nd that--NO other way!!!!! This will teach you along the way as well.....
 
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#4
"Milled" means removing metal from the cylinder base to increase the compression ratio. This is done because higher compression yields more power. Doing this, however, necessitates the use of a higher-octane fuel to control detonation. Which brings me to the explanation of "50/50"... this represents mixing race fuel (112 octane in my case) with premium unleaded pump gas. I indicated in my post on that I was looking for a BASELINE. I was not expecting for dead-on numbers. I was only looking for some approximations to START the jetting process. I appreciate the replies, and understand you points.
 
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#5
After some searching, I found what I was looking for within the Carb Tuning section. For anone else who may be looking too, here it is:


"With a performance pipe/expansion chamber, the air box lid removed and the stock or a performance silencer run a 42/45 pilot, R1174K jet needle in the mid clip position, a 152/155 main jet fine tune the pilot circuit using the air screw."

At least it is ballpark, right?
 

canyncarvr

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#6
I understand what milling means and what its purpose is. What isn't answered is what the squish band is..the angle, the depth, how it's radiused, all that stuff. That is critical when it comes to fuel requirements.

Hopefully it's the head that was milled and not the cylinder base. What would happen to port timing in that case? What about the piston crown-to-head clearance? Your squish band would be really goobered.

...and don't bother telling me what the specs are..cuz that wouldn't tell me a thing. It's the guy doing the work that needs to know what the desired result is and the right way to get there.

Same with '50/50'. I understand that to be probably a mix of race and pump fuel. Thing is, race fuel varies from a-z depending on what is required in the intended application. Some think aviation fuel is 'race gas'.

I wouldn't use CDave's jetting recs for a stock engine just because the mod list fits. Too many unknowns.

If I had the job of sorting out the jetting in a situation as yours, I'd probably start with a 48/165. OEM needle on clip-3 would probably be ok.

I'd buy a box of plugs. ;)

Good luck.
 
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#7
I suppose the whole milling issue would have to be answered by Eric Gorr. I thought he had done base work, but I could be wrong. It is for sure higher a higher C/R. I guess the point is that it is on a race fuel diet, which affects jetting. I will take your advice and buy a box of plugs to get this thing tuned. Now that I have some opinions on baselines, I won't use so may of those things!
 

canyncarvr

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#8
If EG did it I wouldn't doubt the result.

Also, if he did it, I'll bet he could give you a pointer or two on what sort of carb setup you would need.

Again....good luck!
 

KelvinKDX

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#9
ah - CC ... I get so much enjoyment out of reading your replies. 

Almost always good advice.