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New 2019 TX300 Carb Set Up

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I just got a new bike 19 TX300 and need to set the carb up for my area. I will be riding at 0 to 1000 feet of altitude in a desert environment, gotta love the southern Baja. Any basic recommendations to get me started would be appreciated as this is my first two stroke and I want to be as far ahead as possible. The carb is a stock mikuni.

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Read the graham Jarvis carb mod thread it’s a sticky tons of 300 setups start by getting a jd jet block gasket
And go from there

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Do the Jarvis mods (slide notch and holes drilled in the float bowl plug and plastic baffle) right away.  It'll never come close to running well without them.  Once that's done slap in a JD kit or use the chart in the manual for oem type jets and you should be good.  I start at 8k and go up from there so my specs would be useless to you.  Also fwiw rk heads really work wonders in these bikes.

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Do the Jarvis mods (slide notch and holes drilled in the float bowl plug and plastic baffle) right away.  It'll never come close to running well without them.  Once that's done slap in a JD kit or use the chart in the manual for oem type jets and you should be good.  I start at 8k and go up from there so my specs would be useless to you.  Also fwiw rk heads really work wonders in these bikes.

Put the boyesen rad valve in s3 slavens head and sx ignition . I haven’t had to do any carb mods just changed jets its perfectly jetted runs awesome.
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13 hours ago, Rick132 said:


Put the boyesen rad valve in s3 slavens head and sx ignition . I haven’t had to do any carb mods just changed jets its perfectly jetted runs awesome.

Do the Jarvis mods, you are definitely not getting everything from it without them.  There is simply no way a stock carb can keep the main jet supplied with fuel if you run it hard at high rpm and wot.

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Just purchased one myself, I had no issue getting the stock carb dialed in at 300 ft of elevation using the stock settings in the ridiculously hot Southeast.  Did end up one notch leaner on the needle to clean up 0-1/8th throttle blurble.

I agree, stock reeds are crap, daylight showing with 2 hours on the bike.  I'm a Rad valve guy and a factory second from Boyesen is around $115 shipped.  Can't beat it.

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Put the boyesen rad valve in s3 slavens head and sx ignition . I haven’t had to do any carb mods just changed jets its perfectly jetted runs awesome.
How do you like the sx ignition? Which one is it? 250sx or the 300sxs?

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Just purchased one myself, I had no issue getting the stock carb dialed in at 300 ft of elevation using the stock settings in the ridiculously hot Southeast.  Did end up one notch leaner on the needle to clean up 0-1/8th throttle blurble.
I agree, stock reeds are crap, daylight showing with 2 hours on the bike.  I'm a Rad valve guy and a factory second from Boyesen is around $115 shipped.  Can't beat it.
I really liked my rad valve. Great performance.....but.....the radvalve is made for a keihin, even says so on the instructions. In the end what you will have is a small offset on alignment between the engine side of the carb and the rubber boot at the end of the radvalve. That offset, over time, will develop a leak. Im intending on getting a keihin just so i can use the radvalve again. Not that i couldnt now, but there are 2 dimensions that dont line up well. 1- the rubber boot, which would be able to be gotten around better if the aluminum intake port wasnt so long, which requires the boot to be pushed onto the bend of the port, which creates an oval, which eventually will cause a leak because it will keep coming loose.
2- the port itself is bent to accept a keihin. My dad has my 14 te300 currently and i dont feel right going and taking his carb.....unless i know the mikuni will fit the 14. I will tell you now i think the mikuni is longer by the way it pushs the radvalve boot. Probably a 2 or 3 mm difference....BUT, you may need to be inventive to get it to stay tight.

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On 10/4/2019 at 6:16 AM, bikepilot1 said:

Do the Jarvis mods (slide notch and holes drilled in the float bowl plug and plastic baffle) right away.  It'll never come close to running well without them.  Once that's done slap in a JD kit or use the chart in the manual for oem type jets and you should be good.  I start at 8k and go up from there so my specs would be useless to you.  Also fwiw rk heads really work wonders in these bikes.

My 18tx runs fime with stock jets.

i am running 22.5 idle, 450main, and stock needle and clip ht (never needed to touch the needle).

starts easy, idles well, and no probs from 0’ to 9k ft .

seems the bike came with extra jets and needles, I would try that first

Same goes for my buddies ‘19 tx, and my other buddies 19 tc250

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On 9/30/2019 at 9:39 PM, DanDeVries said:

Read the graham Jarvis carb mod thread it’s a sticky tons of 300 setups start by getting a jd jet block gasket
And go from there

what is the importance of this jet block gasket on the 300's only?  

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what is the importance of this jet block gasket on the 300's only?  

Anything that comes with the mikuni The stock gasket deforms and can let fuel leak past throwing your jetting off
Mine ran fine but was deformed when I replaced it
Some bikes it leaks worse than others and can really throw things off
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On 11/28/2019 at 2:49 AM, hondaman331 said:

I really liked my rad valve. Great performance.....but.....the radvalve is made for a keihin, even says so on the instructions. In the end what you will have is a small offset on alignment between the engine side of the carb and the rubber boot at the end of the radvalve. That offset, over time, will develop a leak. Im intending on getting a keihin just so i can use the radvalve again. Not that i couldnt now, but there are 2 dimensions that dont line up well. 1- the rubber boot, which would be able to be gotten around better if the aluminum intake port wasnt so long, which requires the boot to be pushed onto the bend of the port, which creates an oval, which eventually will cause a leak because it will keep coming loose.
2- the port itself is bent to accept a keihin. My dad has my 14 te300 currently and i dont feel right going and taking his carb.....unless i know the mikuni will fit the 14. I will tell you now i think the mikuni is longer by the way it pushs the radvalve boot. Probably a 2 or 3 mm difference....BUT, you may need to be inventive to get it to stay tight.

I'm running a Radvalve on my '18 as is a buddy of mine and have now put about 50hrs on it each and no ill effects with fitment or leaks. Both bikes are running awesome with it and the Mikuni......

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8 hours ago, Wrfrk said:

I'm running a Radvalve on my '18 as is a buddy of mine and have now put about 50hrs on it each and no ill effects with fitment or leaks. Both bikes are running awesome with it and the Mikuni......

The 19 tx has a new subframe that doesnt like the fit. The front of the mikuni doesnt line up or is pushed too far in by rear boot. Either way, 2 guys i know with 19 txs had the same issue, they still use theirs as well. Im going to put mine in with the keihin (its what the rad valve instructions are for) and see if it lines up better. If i have enough time when the keihin comes i will mock them both up to show the issue. Not a huge deal....but it will distort the front boot. Im assuming the lesser amount of subframe material helps the ktm stay lined up better? Not sure, but for the tx of 19 with the new 2 piece subframe its a bit of a fitment issue.

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