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Unread 03-21-2013, 10:33 PM
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Smithers Smithers is offline
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Join Date: Feb 2004
Location: San Luis Obispo, CA
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So someone was monkeying around with the carb jets for some reason and neglected to put the fuel screw spring, washer and o-ring seal back in with it. Why? Because the spring is small but very firm meaning it's a REAL pain in the butt to push back in with the fuel screw because you have to turn the screw at the same time so it will catch on the threads that you are trying to grab to hold it in. It's kinda hard.

Luckily I had a new aftermarket flexible fuel screw that I had been saving for my KTM. The same part will fit in any Keihin FCR carb so I tore the package open and proceeded to install it on the RMZ250. It was very hard to install. The spring was so difficult to push in while turning the flexible screw. It took me a half hour until I was able to get the screw threads to engage the carb body. But I got it.

I kicked the bike with faith and it fired right up and actually idled nearly perfect. It was stumbling a little bit unless I kept on the throttle slightly. Regardless of the idle speed adjuster it was just running a tad rough. With nearly half a turn back out on the fuel screw the mixture was richened up a tad and the bike ran PERFECT. I was shocked. The fuel screw adjustment was really a tiny adjustment when you think about what physically happens when you turn the screw. But it did the trick.

The RMZ250 sounded a lot meaner than I imagined it would. The Pro Circuit pipe really barks loud and hard with the blip of the throttle. With the engine warmed up I wanted to see how well the engine would respond to quick throttle blips. The Honda CRF's I have been messing around with recently have a really weak accelerator pump system which causes the engine to bog when you stab the throttle. If you turn the throttle normal or fast it's not a problem but if you just dump the throttle right off idle you won't be going anywhere too soon. With this RMZ it's a completely different monster. I was really surprised when I turned the throttle fast. It took off! Then I let it idle down all the way and I turned the throttle tube as quick as I possible could rip it open. The sucked just jumped full tilt without any hesitation. I'm very impressed with the carb and it's setup so far that's for sure.

  • I'm just at sea level here in California.
  • Main Jet: #178 (stock indeed)
  • Pilot Jet: #48 (stock is 40!)
  • Everything else is stock except the new fuel screw which has a more aggressive taper
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