1983 XL600R Jetting, So Close...

Trying to dial in my dual carbs. Bike runs pretty well all around, no significant flat spots or stumbles, pulls to redline fine. Starts on the first kick every time, no problem. Only mods are removed snorkel and backfire screen. Some sort of aftermarket exhaust, but I don't know what (no name, almost looks like a straight pipe with a screw on baffle cork at the end...) Air screw 1 turn out. She seems a bit lean past 1/4-1/2 throttle. Front tire almost wants to lift in first, but then after 1/4-1/2 there's this flatter response (front tire stays down but still pulling), then after 1/2 it's like a turbo kicks in and she's off, pulling hard again. All around it feels like the the mains in each carb are either a hair lean, or the needle in the primary needs to be raised a notch. Midrange and top end have more power to give...

Curious what other's experience with the dual carbs have taught them. Anybody with similar mods, what mains did you settle on? Does it sound like raising the primary's needle a notch could do the trick, or should I raise the main sizing on each a hair?

 

Edited by Phaedru5
Trying to dial in my dual carbs. Bike runs pretty well all around, no significant flat spots or stumbles, pulls to redline fine. Starts on the first kick every time, no problem. Only mods are removed snorkel and backfire screen. Some sort of aftermarket exhaust, but I don't know what (no name, almost looks like a straight pipe with a screw on baffle cork at the end...) Air screw 1 turn out. She seems a bit lean past 1/4-1/2 throttle. Front tire almost wants to lift in first, but then after 1/4-1/2 there's this flatter response (front tire stays down but still pulling), then after 1/2 it's like a turbo kicks in and she's off, pulling hard again. All around it feels like the the mains in each carb are either a hair lean, or the needle in the primary needs to be raised a notch. Midrange and top end have more power to give...

Curious what other's experience with the dual carbs have taught them. Anybody with similar mods, what mains did you settle on? Does it sound like raising the primary's needle a notch could do the trick, or should I raise the main sizing on each a hair?

 

What jets are you running now?

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58

115

128

Thinking I might bump the primary main up to 125. There's the flat spot...

58
115
128

Thinking I might bump the primary main up to 125. There's the flat spot...

Yup, lean on primary. I'm at 58, 125, 125 but have run it as rich as 128, 128.

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Right on. The Honda dealer is convinced my 115 is actually a 125... I think he's blind. I decided to chance his word and went with a 128 in the primary, 130 secondary. 1 turn out on the air screw. Bike is muuuuch happier. Good, smooth response closed to open. Probably a bit rich overall, but the more immediate throttle response in the mid-full is awesome. 

You think I might foul the plugs running this rich? Again, no snorkel/backfire screen +aftermarket exhaust. I'm hoping there's enough airflow. I guess I can check the plug in some miles...

Why'd you settle on 125/125? / What are your mods, if any?

Edited by Phaedru5

With 128,128 I was getting a bog on throttle snaps when it was warm out so I dropped it first to 125,128 and that was better but I ended up going 125,125 for the most universal performance across temps and elevations.

Wiesco 10.5 piston, fmf powerbomb/powercore 4, uni filter.

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Out of curiosity, backfire screen or no?

Out of curiosity, backfire screen or no?

Yes. I'm not a fan of fire between my legs.

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For sure. Depends on my mood...

The extra air flow is likely why mine is so thirsty. Thanks for all of the info, man. Super helpful!
[Edit:] Took her on the freeway for a longer ride. Definitely a bit too rich. Getting a bog on blips when both carbs open. My conjecture about the backfire screen was off. Will try the 125/128 combo next.

Edited by Phaedru5

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