Mikuni S4 needle jet help

Duncster316
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2/18/2020 3:52pm
Hey all. trying to get my TMX set up with AJ’s specs for the spring on my tc250. I bought an s4 needle jet part #784-13005-s4. The oem s1 has a groove down the side to accomidate a little nub that sticks out. the replacement part doesnt have the groove and does not fit. Is there another part number jet that works? Having a bitch of a time just finding them. Thanks for any help. To clarify, does anyone have the proper S4 part number and a possible place to buy one?
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AJ565
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2/18/2020 6:31pm
Have some pics of what you’re talking about?
AJ565
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2/18/2020 6:58pm
55431021400 Is the part number I found for the S4 needle jet that I’m using.
digger
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2/19/2020 7:20am
Hey all. trying to get my TMX set up with AJ’s specs for the spring on my tc250. I bought an s4 needle jet part #784-13005-s4...
Hey all. trying to get my TMX set up with AJ’s specs for the spring on my tc250. I bought an s4 needle jet part #784-13005-s4. The oem s1 has a groove down the side to accomidate a little nub that sticks out. the replacement part doesnt have the groove and does not fit. Is there another part number jet that works? Having a bitch of a time just finding them. Thanks for any help. To clarify, does anyone have the proper S4 part number and a possible place to buy one?
You need a 914 series needle jet for the late model TMX-x carbs. I bet you ordered a 633 series needle jet, which is not correct, as you have found out. AJ has given you the correct KTM part # https://www.motosport.com/oem-parts/part-number/55431021400?mmysource=k…
Duncster316
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2/19/2020 11:02am
Thanks so much guys, I could not find the part after a bunch of searching! Looking forward to getting this carb lined out to go with my new RK tek head.

The Shop

AJ565
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2/19/2020 12:16pm
Thanks so much guys, I could not find the part after a bunch of searching! Looking forward to getting this carb lined out to go with...
Thanks so much guys, I could not find the part after a bunch of searching! Looking forward to getting this carb lined out to go with my new RK tek head.
I'm not sure how close the jetting will be with the head. If its higher compression than stock you're gonna lose some over rev, which already isn't great on this engine.
Duncster316
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2/19/2020 2:44pm
I don’t think it’s much if any extra compression. Different shaping inside. Will run it some and report back. 👍
YZed250
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2/20/2020 8:37am
I don’t think it’s much if any extra compression. Different shaping inside. Will run it some and report back. 👍
Interested to hear how it goes. Rave reviews for RK heads for the XC/XCW guys who all start with low compression and wide squish from KTM/Husq. The TC and SX come standard with it quite a lot higher/tighter from the factory but I'm RK will make some difference.
AJ565
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2/20/2020 8:59am
I don’t think it’s much if any extra compression. Different shaping inside. Will run it some and report back. 👍
If you ever come down to the Austin area to ride give me a heads up. You're welcome to put a few laps on my bike to compare as well.
1
Duncster316
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2/20/2020 11:19am
I don’t think it’s much if any extra compression. Different shaping inside. Will run it some and report back. 👍
AJ565 wrote:
If you ever come down to the Austin area to ride give me a heads up. You're welcome to put a few laps on my bike...
If you ever come down to the Austin area to ride give me a heads up. You're welcome to put a few laps on my bike to compare as well.
👍 Definately will do, thanks AJ!
AJ565
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2/23/2020 6:01pm
You get to ride it with the new jetting yet?
mxstate
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2/24/2020 5:59am
AJ565 wrote:
You get to ride it with the new jetting yet?
Same question here!
I run AJ specs on my 19 and it's really good. Really cleaned up the issues and no more inconsistency.
It's a bit of a beast now and I added a flywheel weight as a first way to make it more manageable (C class level here)
I'm tinkering with the idea of an RK head too since reviews seems to rave about how it helps with a more linear power delivery.

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