Scrambler 50 tuning help please! - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-01-2004, 06:54 PM
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Scrambler 50 tuning help please!

I'm trying to get a little more outta my scrambler 50. I've put on a UNI filter and outerwear, and removed the oil injection. It has a 19 tooth front sprocket from a 90. The rest is stock. CDI box jumper off of course. My question deals with jetting. I have ran a 105 jet in it, and it runs up to WOT but seems a little boggy reaching top end. I've also tried a 90 jet, and it wont run WOT(just bogs and dies) sure runs great up to the boggy point though! Plug looks good with either jet? Do I need to be doing something with the needle? I haven't touched it yet. I guess it must be either too rich or lean in the upper midrange rpms. Any suggestions from you experts!?? I believe the E-Clip is in the #3 slot/ middle position.

The 90 jet must be too lean to have it not run WOT right?

Any suggestions greatly appreciated! Thanks!

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post #2 of (permalink) Old 04-07-2004, 06:15 PM
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Re: Scrambler 50 tuning help please!

The needle will only control fuel mixture from about 1/4 to 3/4 throttle only the main jet after 3/4 throttle. I think if its lazy only at full throttle you are still too lean on the main.Did you put in a new plug and make 1 full throttle run after the engine got warm and check the plug reading then?That is the accurate way to check main jetting.If you go up on the main and then it gets lazy in the middle you may have to move the needle.up on the clip to lean jetting and down on the clip to richen it. by the way my 6 year old boy has a scrambler 50 a 2001. He just started racing and has to run with the 90's usally they dont have enough 50 riders and I am starting to heavily modify his.I have never been a fan of that stock carb im going to a 20mm.Hope I could answer your jetting question. Also when you read the plug look at the bottom of the insulator and it should be almost a chocolate brown at least thats what the guy who builds my race motors says.
post #3 of (permalink) Old 04-08-2004, 03:27 PM
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Re: Scrambler 50 tuning help please!

Mastertech1 is right-on only I'd look for a light tan color on the base ring. Regardless, it sounds like you're running too lean so follow Mastertech1's advice and try a 110. Richer is better than leaner since leaner can melt pistons and / or head gaskets.

If you want more acceleration, install lighter variator rollers. Start with 5.4g weights. Some folks do well mixing 3-4.2's and 3-5.4's (there are 6 rollers total so be sure to install them in alternating order). Going to the 19t front sprocket was a good idea. Next, consider going to a smaller rear such as a 31. Some run as small as a 28, but usually with an 18 front. Don't go too small because the bike doesn't have the power to drive a smaller sprocket especially on hilly terrain such as a motocross track.

If you want more snap off the line or out of the corners, install stronger springs in the clutch. Spring tension controls the rpm at which the clutch engages, or the "stall speed". Setting the stall speed higher moves the running rpm more within the torque curve. Best results are obtained when changing both the rollers and springs. No need to change the big spring (torque driver spring) unless you add a pipe or do cylinder / head mods.

Performing these mods will really wake up a stock bike.
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