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4T Carb Tuning


mcman56
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I have a 2016 300 with the standard pipe and muffler.  I have adjusted the jetting and it runs great with one exception.  Occasionally, when opening the throttle from idle it will stall.  It does not pop through the intake but instead you hear what sounds like fuel burning in the exhaust.  It sounds very similar to a gas barbecue being lit.  This happens at lower idle settings, below 1200 rpm.  At higher settings up above 1400 it does not happen.  Is this rich or lean?     

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I am thinking a tickover speed down below 1200 is kinda low, especially for not having any form of accelerator pump on the carb. Not sure about your bbq sound...double check your carb fitment to the manifold?  Seen on several occasions were motor had ''puffed''....it off the boot and still run...just not well, make sure your rubber block off plugs on carb are still on??  

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11 hours ago, lineaway said:

 Did you re jet and install the thumb screw?

If you decide to do this and need any help (pics and step-by-step), let me know.  I just did all of this on my 4T and documented and took pictures of everything since I was able to find very little on the web regarding how to.  It's not hard to do, but it seems that for every thing you want to do, there are 5 additional thing you have to do to get at what you're wanting to do.

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I have been through the carb and tried different jetting plus have the adjuster screw.  Initially, I had to run a rich idle to prevent bogging.  Once I raised the needle, the bog tendency went away so I leaned out the idle.  I'm now running a 22.5 pilot and since the symptom is lean will go up one size to see if improves.     

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On 6/8/2018 at 10:23 AM, mcman56 said:

I have been through the carb and tried different jetting plus have the adjuster screw.  Initially, I had to run a rich idle to prevent bogging.  Once I raised the needle, the bog tendency went away so I leaned out the idle.  I'm now running a 22.5 pilot and since the symptom is lean will go up one size to see if improves.     

I'm at sea level on the gulf coast.  My bike was super lean when I bought it.  PO lived in Colorado Springs and had it set up for riding 10-13,000 feet.  Here are the changes I made to get it to run well at sea level:

Rejetted carb 25 pilot, 132.5 main (from 27.5/120)

Changed carb spring from blue to silver

Raised needle (dropped clip to 4th position)

Pilot screw 2 turns out

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I had a 130 main so went to 25 and 130.  Clip is at 4th position.  Spring looks silver.  What spring is OEM?  What is the blue spring for?  It is lighter for quicker opening?  I have ridden at sea level and 5500 feet and ti seem sOK

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On 6/10/2018 at 9:56 PM, mcman56 said:

I had a 130 main so went to 25 and 130.  Clip is at 4th position.  Spring looks silver.  What spring is OEM?  What is the blue spring for?  It is lighter for quicker opening?  I have ridden at sea level and 5500 feet and ti seem sOK

Both springs came with my bike.  From the research I've done, blue spring at elevations > 5,000 ft, silver spring at elevations < 5,000 ft.

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  • 3 years later...

Hello All,

 I am just digging into this project. My question is, do I need to remove the carburetor from the bike (basically disassembling the entire bike) to remove it? Or, is it possible to loosen the clamps and swivel the carburetor to access the bottom and the jets? Sorry for the cluelessness.🤪👍

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