Oh look, another jetting question

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8/31/2017 8:36 AM

Hey all, been working on my project RMX 250 for a while and I'm finally getting somewhere. Its a 92 RM250 bottom with the rmx250 top end, Pro circuit platinum head pipe, pro circuit 304 silencer, Vforce3 Reed valve, UNI air filter with the air box lid removed. Using an Iridium Denso IW24 spark plug.

I had an issue with the bike after rebuild bogging when getting into the main jet area of the throttle. (bought it as a basket case essentially). Its got the factory Mikuni TM carb. I took it apart the other day fully and found a few things, its got a 290 main jet, and the metering needle clip was at the bottom position (i dont know if thats considered 1st or 5th) but I do know that position was letting as much fuel in as possible. With research from FMF's website (bare with me while I get to my point), Its recommended setting would be a 260 main jet with the clip in the 3rd position. So I moved the clip up to the 3rd position and its remarkably better. I can get into the power band finally and see all my hard work coming together. BUT, its still not 100%!

It bogs and starts smoking more up top, just like it did before the needle position change. I think Im on the right track, seeming like its getting TOO much fuel IMO if the only change I did was technically make the needle go further down into the main jet. Pro circuits website though, recommends a 360 main jet!!!! Umm, that seems like wwaayyyy too much fuel as I have a 290 now with issues as it is..

So in quick terms with this info, my questions are...

From top to bottom of the needle, which would be considered position 1 to 5?
Does this sound like too much fuel being a problem and Im on the right track?
Should I try a 260 main jet over the 290 thats currently in it?
Is there a better spark plug of choice?
Should I ditch the TM and install the PWK38 Air striker I have on order and try to tune it instead?

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8/31/2017 12:42 PM

You've already done some work so keep at it with this carb (imo). Yes, it does sound like your main jet is still too rich. Especially if you are wide open and you are getting smoking/bogging. Try the 260 or even a 270 so it isn't so sever of a change and see where you're at. Good luck

ps- The top of the needle is 1st clip (leanest) and richest is the bottom (usually 5th clip)

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8/31/2017 3:01 PM

Check your plug color. If it's black, you are still too rich. Older Suzukis are notorious for being rich from the factory, so a 290 is probably bad, being even richer. Maybe go back to the 260 and ride it for a while, being careful not to put too much load on it. If the plug is white then you've gone too lean.

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Braaapin' aint easy.

9/3/2017 10:14 AM

Reading your other posts about the project you have taken on had me worried for you.
I have some experience with your project trying to mix and match RMX and RM.
At the point you are now, with the info you gave I might follow these steps?

Two people makes this test easier.

1. start cycle. if it bogs and you think it's fuel starvation apply the choke and see if the bog disappears with the huge fuel hole the choke allows for massive amount of extra fuel, is your bog gone with the choke or way worse?

2. remove airbox, see if bog is better, rev cycle and apply air hose pressure of about 5 psi at carb intake and see if the extra turbo air supply makes the bog go bye bye.

After determining if you are rich or lean you can adjust the carb.
If the extra fuel, or the extra air does nothing the bog is something else...

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9/3/2017 6:23 PM

How are the crank seals?

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Tomac and/or Anderson for 2020.....

9/3/2017 8:25 PM

seth505 wrote:

You've already done some work so keep at it with this carb (imo). Yes, it does sound like your main jet is still too rich. Especially if you are wide open and you are getting smoking/bogging. Try the 260 or even a 270 so it isn't so sever of a change and see where you're at. Good luck

ps- The top of the needle is 1st clip (leanest) and richest is the bottom (usually 5th clip)

Thanks, I plan to put a 260 in it and try again with my exact setup now. It's been hard to tune it without being able to ride it. This bike was essentially a ground up build. Once I put the 260 in I think it'll be on track.

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9/3/2017 8:26 PM

Falcon wrote:

Check your plug color. If it's black, you are still too rich. Older Suzukis are notorious for being rich from the factory, so a 290 is probably bad, being even richer. Maybe go back to the 260 and ride it for a while, being careful not to put too much load on it. If the plug is white then you've gone too lean.

My plugs actually wet when I shut it off. Miraculously it starts back up well. I'm going to try the 260

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9/3/2017 8:27 PM

speed_racer wrote:

Reading your other posts about the project you have taken on had me worried for you.
I have some experience with your project trying to mix and match RMX and RM.
At the point you are now, with the info you gave I might follow these steps?

Two people makes this test easier.

1. start cycle. if it bogs and you think it's fuel starvation apply the choke and see if the bog disappears with the huge fuel hole the choke allows for massive amount of extra fuel, is your bog gone with the choke or way worse?

2. remove airbox, see if bog is better, rev cycle and apply air hose pressure of about 5 psi at carb intake and see if the extra turbo air supply makes the bog go bye bye.

After determining if you are rich or lean you can adjust the carb.
If the extra fuel, or the extra air does nothing the bog is something else...

Will do, thanks for the help. Considering the changes I've made it seems opposite of fuel starvation. Everything's gone smooth with engine setup, it's just the carb that's been a learning process.

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9/3/2017 8:28 PM

BobPA wrote:

How are the crank seals?

Crank seals are fine. Entire bottom end and top end is fresh. No leaks.

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