Lean and rich - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 7 (permalink) Old 01-05-2019, 03:04 PM Thread Starter
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Lean and rich

I'm at a loss. I had put some K&N filters (not pods) on my bike, and some Vance and Hines full exhaust. I had decided to rejet my bike because I noticed I was getting some hesitation and overall running bad.

Pulled the carbs, cleaned and rejetted.
138 main jets
40 idle jets
2 shims on slide needle

I believe I have the carbs synced, seems to idle smooth.

The front cylinder runs rich and nothing i do when adjusting the air mixture screw seems to do anything.

The rear cylinder runs lean and same thing when adjusting the mixture screw.

I've set both sides to 3 1/2 turns out.

I've searched the forums but I haven't found anything similar to my issue... or I may have missed it...

Please help, the only thing I can think of at this point is taking it to the shop for them to charge me $100 an hour and they took 2 and a half hours changing a broken exhaust stud...
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post #2 of 7 (permalink) Old 01-05-2019, 03:10 PM Thread Starter
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Also should mention I had gotten a gunson color tune
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post #3 of 7 (permalink) Old 01-06-2019, 12:47 PM
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Quote:
The front cylinder runs rich and nothing i do when adjusting the air mixture screw seems to do anything.
The air screws only affect idle, and low rpm mixture, so about 1000-2500 rpm. Around 2500-3000 rpm, the pilot jet circuit transitions toward the main jet circuit. Adjustment of the screws will have no effect on mixture above the transition rpm.

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post #4 of 7 (permalink) Old 01-06-2019, 10:47 PM
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You may need to make sure the needles aren't swapped around, first thing that comes to mind where one is unusually rich and the other is unusually lean. How do you know which is rich and at what RPM does the rich/lean mixes show up?

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post #5 of 7 (permalink) Old 01-10-2019, 10:50 AM Thread Starter
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Originally Posted by ubertalldude View Post
You may need to make sure the needles aren't swapped around, first thing that comes to mind where one is unusually rich and the other is unusually lean. How do you know which is rich and at what RPM does the rich/lean mixes show up?
When i re-jetted the carbs i did everything one at a time so when putting the shims under the needle i only took one out and then put it back in so i didn't get anything mixed up.

I noticed the different mixtures due to my front cylinder spark plugs being carbon fouled, and my rear being nearly white on the tip. I got a Gunson colortune because i saw people on here rave about it (essentially a spark plug with a glass window to see whats going on inside the cylinder). When using that it verified what i saw on the plugs. The front cylinder was a bright orange flame and the rear was an extremely nearly white blue. No matter what i did with the adjustment screw it doesn't seem to change the mixture and these conditions seem to be at idle and low rpms. I thought about maybe going back to my stock idle jets but i'm not sure what that would do with the rear cylinder being too lean...
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post #6 of 7 (permalink) Old 01-10-2019, 12:46 PM
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Does the color on the regular spark plugs agree with the colortune readings?

Only thing I can think of right now, is to adjust the sizes of the pilot jets by one step in the directions needed, assuming all else is correct.

When you adjust the air screws, is there any change in the idle? If you close the screw and idle isn't affected, that probably indicates a clogged circuit.

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__________________________________________________ ____________
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post #7 of 7 (permalink) Old 01-10-2019, 04:51 PM Thread Starter
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Does the color on the regular spark plugs agree with the colortune readings?

Only thing I can think of right now, is to adjust the sizes of the pilot jets by one step in the directions needed, assuming all else is correct.

When you adjust the air screws, is there any change in the idle? If you close the screw and idle isn't affected, that probably indicates a clogged circuit.
They do, and i thought about changing the pilot jets. I'm just worried it may be signs of a bad carb.. As far as i can tell it seems like it does well after about 2500 RPM. I guess i'll try to order some more pilot jets
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