Tons of fun one little issue - experts?

Yellow0206

XS400 Enthusiast
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So I have been riding the heck out of this thing and enjoying it a ton. Have been tuning and it runs cery while with one exception, some hesitation/ burbling at 5500-6500. Runs perfect and clean below and above. Have replaced plugs, points, condensor, coils, have rebuilt cleaned carbs, running stock airboxes with new filters, exhaust is aftermarket 2 into 2 with megaphones and baffles, no crossover. Compression is very good about 170psi in both. Timing is perfect, carbs have been synchronised with manometer, valve clearances are correct. I started with 150 Jets went to 145 now at 142.5. Very happy with looks and performance of bike after a lot of work but would like to see if can get rid of this burble.

Any thoughtful ideas based on experience are welcomed.
 

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Those rpm's are just off the jet needle and the start of the mains. What clip do you have the needle on? Could be the sound of the exhaust at those rpm's or some type of frequency/flow sound.
 
Those rpm's are just off the jet needle and the start of the mains. What clip do you have the needle on? Could be the sound of the exhaust at those rpm's or some type of frequency/flow sound.
Hi Chris thks for responding altho i did not say so i was thinking along same lines - I do not remember seeing that the needle was adjustable when I last had carbs out and tops off - Im pretty sure they are the stock 77 XS400D BS34 carbs - did they for sure have adjustable needles? If so I am thinking I am getting rich condition as needle pulls out completely so I would need to drop needle down to lean it out if I can right? Thks - hope u r riding a lot...
 
77-79 xs400 bikes stock carbs are adjustable needles. Yes, dropping the needle will lean it out.
 
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