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XR440 Pumper Carb jetting?

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Hi all,

I have an XR440 with a Pumper Carb that I just bought about a month ago.  Are any of you guys using a Pumper on a 440 and can share your jetting with me?  Mine is hard to start and the throttle screw is all the way out and I'm wondering if my pilot needs to be adjusted.  I currently have a 17.5 pilot and 130 main. I'm also basically at sea level (700 ft).

Thanks,

Brandon

Edited by OrangePeeled

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What pumper carb are you using?

I'm assuming a TM36, I have a TM40 and I'm running a 12.5 I think at 100 feet. You have slightly higher air velocity in a 36 so my guess would be you are Rich. You say your throttle screw is all the way out, I don't know if you mean throttle or mixture.

Mikuni has a Free downloadable manual for the TM pumper carbs and it is very helpful.

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4 hours ago, firstplacephoto said:

 

I think I ran into one of his posts, but didn't see a specific pilot mentioned.  I'll continue to do some more digging.  Going to call XRs only today 

2 hours ago, Firestone said:

What pumper carb are you using?

I'm assuming a TM36, I have a TM40 and I'm running a 12.5 I think at 100 feet. You have slightly higher air velocity in a 36 so my guess would be you are Rich. You say your throttle screw is all the way out, I don't know if you mean throttle or mixture.

Mikuni has a Free downloadable manual for the TM pumper carbs and it is very helpful.

I grabbed that manual.  I need to read through it again.  Yes, I have the TM36.  I meant the pilot/idle screw, not sure why I said throttle screw.  

Does anyone ever mess with the air pilot jet?  Seems like I only ever see people talk about the pilot and main jets.

Thanks, guys!

Brandon

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I think this is the manual Firestone spoke of, it's what we use for tuning the TM36. http://www.mikuni.com/pdf/hs40_manual.pdf

We need to know what you're calling the "throttle screw". Look at the nomenclature in the .pdf above.

For A/P adj screw #1, part #61, turn it all the way in, bottoming against its spring.

Part #50 is the idle speed screw.

Part #29 is the pilot fuel screw.

It's easy to flood the carb if you're twisting the throttle a lot while trying to start it, so don't do that. Set the choke to ON. Kick the engine over several times while holding the manual decomp., release decomp, bring the engine to TDC, give a strong kick and near the bottom of the kick, wick the throttle open slightly. Must make your starting kick from TDC every time.

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9 minutes ago, OrangePeeled said:

I think I ran into one of his posts, but didn't see a specific pilot mentioned.  I'll continue to do some more digging.  Going to call XRs only today 

I grabbed that manual.  I need to read through it again.  Yes, I have the TM36.  I meant the pilot/idle screw, not sure why I said throttle screw.  

Does anyone ever mess with the air pilot jet?  Seems like I only ever see people talk about the pilot and main jets.

Thanks, guys!

Brandon

You're still confusing. It's either the pilot or the idle screw. Which is it? The pilot is not an idle screw, nor does the idle act like a pilot.

The air jet is not messed with.

Edited by Trailryder42
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With the idle adjuster screw(white knob) backed all the way out, the slide is not raised enough to be able to provide enough air/fuel mix to idle, let alone start and run.

The pilot screw(fuel screw) adjusts the mix provided by the pilot jet. It is the screw at the front of the carb bowl, pointing down. Part #29 in the schematic of the above .pdf manual.

To get the idle speed knob set so it will idle, get the bike started using the method I described above. Hold partial throttle to keep it idling. Turn the white knob IN til it takes over and holds idle without you having to do it.

You need to determine how the fuel screw is set, so at some point, turn it all the way in til it lightly seats, counting the number of turns to do so. Then return it to where it was. That's your baseline setting.

Mikuni TM36.JPG

Edited by Trailryder42
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Ah-ha!!!!  I see now.  Thank you for taking the time to make this graphic!  That is a huge help.  I'll have to check tonight to see where my fuel screw is set.  Going to grab a rebuild kit and ultrasonic clean the carb while I'm at it, too.

Brandon

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