Fat on both ends, lean in the middle? Carb theories.

Halftwist

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So I’m so far from stock and spec on this bike what with the two into one intake manifold, one carb, open/slightly baffled pipes, uni air pods, gonzo ignition, etc, I won’t even bother you with the exact settings, jet size and air/fuel mix.(unless you ask 😂) . My question is how these motors behave under a certain condition, lean or rich. BS38 is the carb.

Timing, cam chain tension, and valves are dead on.

I have the bike idling well. Steady roll on the throttle off idle it takes off smoothly, sharp crack of the throttle it stutters once, kicks back through carb once, and then away we go. What is she tryin to tell me.

Another issue. Using the idle speed adjustment screw so I know it’s steady, I’ll bring the bike to about 1/3 throttle it will run steady for about 3 seconds than the rpm’s will begin to slowly climb to the heavens. Is this a lean issue? I wonder if the two issues are the same and the needle needs lifted some more but I am already on the lowest(richest) slot. Maybe a shim.
 

jpdevol

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I think the last bit describes the slide catching up with the throttle plate opening and the nature of the beast. As to jetting :shrug:, but general rule-of-thumb is to keep going richer (main jet) until it gets worse, then back-up. CV carbs aren't known for liking "snappy", abrupt throttle opening - that may also be nature of beast, especially with that manifold
 

Halftwist

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I think the last bit describes the slide catching up with the throttle plate opening and the nature of the beast. As to jetting :shrug:, but general rule-of-thumb is to keep going richer (main jet) until it gets worse, then back-up. CV carbs aren't known for liking "snappy", abrupt throttle opening - that may also be nature of beast, especially with that manifold
I’m probably just asking too much out of that poor carb
 

gggGary

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Guess I'd try one up on the pilot, drop the needle a slot or two, go from there. what you normally do if the needle's all the way up.
Two into one intakes often pool fuel at a low spot. That puddle will gradually get used up (causing rich running) when it's gone, mixture leans, revs increase. Try closing butterfly a bit more with the idle speed screw, richen idle mix screw a bit. adjust from there.
 

Halftwist

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Guess I'd try one up on the pilot, drop the needle a slot or two, go from there. what you normally do if the needle's all the way up.
Two into one intakes often pool fuel at a low spot. That puddle will gradually get used up (causing rich running) when it's gone, mixture leans, revs increase. Try closing butterfly a bit more with the idle speed screw, richen idle mix screw a bit. adjust from there.

I was wondered about fuel puddling at low rpm’s with the bends in the intake I have. Fuel “deatomization” maybe. Higher velocity at higher rpm’s and the vacuum pulses become clearer for the carb.

I’ll try what you suggest, I think I understand the idea. Not sold on the two into one especially with the 38 but I’ll continue to try to “fix” what some really smart Japanese guys figured out forty years ago. What did they know anyway😂
 

Jim

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I have the bike idling well. Steady roll on the throttle off idle it takes off smoothly, sharp crack of the throttle it stutters once, kicks back through carb once, and then away we go. What is she tryin to tell me.
Just to answer your question on carb theory.... that's generally a lean condition.
Since it's just off idle, what Gary sez above. Richen the mix screw a bit and maybe one up on the pilot.
 
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