A few times after short runs the bike (1958 M18S) won't fire. I have taken the plug out and it is very sooty. Once I clean it and put the plug back in she fires first kick. I am thinking the carb needle is in the wrong (too high) position as, according to what I have read, from 1/4 to 3/4 throttle the needle controls the mixture. The strange thing is that various threads I have read and the manuals say the the needle should be in the middle position. The needle in my carb has 5 grooves (I thought normally 3) and it was already positioned in the second from top groove. So I have moved it down to the last groove. No test ride yet given the weather. I assume the carb is a 389/1 but the only stamping I can see is "N31" on the underside of the flange. The bore is a little over 1.1" so I guess the correct 1 5/32". My questions:
- Is the stamping N31 for a 389?
- Is the needle with 5 grooves wrong?
- Should I be doing something else to stop the carboning up?
Thanks for your thoughts.
Plug carboning up - needle position
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- dave16mct
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Re: Plug carboning up - needle position
You may have the needle from a 376. For a 389 it should be 106mm long and stamped with a 'D' near the top. 5 grooves is correct.
Dave
Dave
- Joker_Bones
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Re: Plug carboning up - needle position
At a little over 1.1" bore... Could be 1 1/8" bore?
Many more 1 1/8" bore 389s out there than 1 5/32
Many more 1 1/8" bore 389s out there than 1 5/32
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Re: Plug carboning up - needle position
Yes a 376 needle is 95mm long and is stamped 'C'. It will make a 389 carb bike run very rich.
Dave
Dave
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Re: Plug carboning up - needle position
Great Dave. I will check next time I remove the tank.