4 into 1 Exhaust and Flat Spots

[danny01975]

82 GS1100 GK. Stock pilot jets. One size up on the main jets. Delkevic 4 into 1 exhaust with the center baffle removed. Bike idles perfectly and runs great overall. However, it has a flat spot in the midrange under acceleration. I read somewhere here on an old thread that 4 into 1's can do this. Is that so? And if so, can it be eliminated by raising / lowering the needles? Also, how would I know which way to go if so?

[zed1015]

At the point of hesitation feather the choke ( enrichener ) .
If the running improves you are lean and if it worsens you are rich.

[Rijko]

did you sync the carbs for a 4-1 ?
They need to be equal (different from standard sync)

[Nessism]

Almost certainly lean. To lift the needle, reduce the thickness of the plastic shim that's on TOP of the needle clip. Do NOT stack washers under the clip, that does not lift the needle.

[danny01975]

did you sync the carbs for a 4-1 ?
They needs to be equal (different from standard sync)

I did not! I read the service manual for carb sync and I believe the middle two should be different from the outer two. Not sure if it’s higher or lower as it just says the balls should be just below the midline on the special vacuum tool.

I didn’t know they needed to be the same. Will give that a shot. Along with the above listed comment about feathering the enrichener.

[danny01975]

Almost certainly lean. To lift the needle, reduce the thickness of the plastic shim that's on TOP of the needle clip. Do NOT stack washers under the clip, that does not lift the needle.

I did read that in the carb rebuild guide I found here. How do you know how much to reduce it? By how many tenths of a mm should I step down each time?