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94 KX250 jetting


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Gradually tearing down my recently acquired KX250. This evening I pulled the carb but didn't have time to pull it apart. I'll check the jetting tomorrow but wanted to check (for reference) what are stock jets - main and pilot, needle and clip position, and airscrew turns out.

For reference it came with a Pro circuit pipe which I've replaced with a stocker for the bottom end pull. I believe reeds are stock as well - but I'll find out for sure tomorrow. I'll be riding at less than 3000ft and temps between 50 and 85.

My question for more experienced tuners - any recommendations for a starting point for the jetting? Or, is stock jetting OK?

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Thanks Shrub. I'm actually going back to the stock pipe for a while because I like to ride on the bottom end. So, my question really is - is the stock jetting actually ideal for a stock setup or have experienced home-tuners come up with a better plan?

I looked at the PC recommendations and they recommend a leaner MJ (158 vs 165 stock) and the same PJ (45) for the 94 (with the PC pipe). That makes me wonder if stock jetting was just too fat to begin with?

Also, if I go with an aftermarket reed (i.e. Boyesen using stock cage) will the recommended jetting change along with it?

Also, saw that PC recommends the thinner head gasket for the 94. Is that a blanket recommendation for the 94 in general or only with the PC pipe?

Thanks again for the help.

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Thinner head gasket could be suggested to correct squish volume. I personally have not seen a reason to change a mx smoker's jetting simply due to expansion chamber changes. Silencer length and whether or not a krizzman spark arrester is included can require jetting changes.

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Stock silencer (or equivalent PC304) and no sparky on this one.  I pulled the carb apart and found a couple sprises.  Initially I thought all was dead stock (#7 slide, N1EE needle, 3rd slot) because it looked and felt like it had never been touched.  MJ is 165 as stock but the PJ was reduced to a 42.  In addition the airscrew was turned 2-1/4 turns out.  Needle and float/needle look good.

 

Wonder if that's why it was a bit hard starting?  Would take 6 or so kicks and even then I'd have to blip the throttle if the choke was off.  Had to set the idle higher than I like to keep it running.  I've done a lot more tuning on 4Ts, but it seems like a smaller PJ would warrant fewer turns out rather than more turns out on the airscrew.

 

If nothing else, I'll replace the 2 jets as I don't trust them looking clear.  I may pick up a 158 and 160 mains, and definitely a 45 pilot.  I've set the airscrew back to the PC recommended 1.5 turns out.

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Daily update - took the reed cage off this evening. Glad I checked. The corners are worn/broken off 2 of the petals so I suspect that may have influenced some hard starting as well.

Any quick recommendations on aftermarket reeds to fit the stock cage? I've seen Boyesen makes a couple sets.

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Daily update - took the reed cage off this evening. Glad I checked. The corners are worn/broken off 2 of the petals so I suspect that may have influenced some hard starting as well.

Any quick recommendations on aftermarket reeds to fit the stock cage? I've seen Boyesen makes a couple sets.

Whatever is cheapest. OEM or boyesen super stocker. I found a good deal on VF3 new out of box for $75 so I jumped. My OEMs still ok so I'm not burning to know if there's a difference. Most say rad valve for low mid and VF3 for more throttle response and top end. Only bolt on I believe in is the pro circuit platinum pipe. Effect was very noticeable over OEM.

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The Rad valves are tuned specifically for that year machine.  The V Force stuff is "universal".  My 94 is stock, stock jetting and rips.  So start with new reeds and stock settings and go from there for your elevation.  I haven't rode my 94 in colder weather, but all my other KX250's (98, 00, 05) did not need any rejetting for temps.

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Thanks gents. I'm looking at the Boyesen reeds made for the stock cage as recommended. Less expensive than stock and I don't have the need for improved performance at all. Honestly, any new reed is going to work better than mine which are missing a couple corners.

Jeekinz - is your 94 jetted at 165/45? I was starting to think stock jetting was fat because I've seen recommendations at 158 or 160 for the main.

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Thanks.  I'll stick with the 165 and giver her a try.  I am substituting a stock 45 for the 42 I found in the carb.

 

Found a set of Boyesen Pro series (carbon upper, fiberglass lower) reeds for $30 shipped on ebay.

 

and mine will never see carpet....

Edited by dukesilver
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