Carb tuning problems - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 58 (permalink) Old 04-04-2014, 04:14 PM Thread Starter
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Carb tuning problems

A few problems to list with a little history:

Ear shaved, and custom exhaust with 8" baffles.

Inline filters on the fuel line. Persistent issue I notice is that one filter stays filled with fuel, while the other stays empty (while fuel still passes through it).

I would think maybe there is a float problem? This would play into the next issue:

I upped Jets to 40/140 and had severe pop on deceleration. I've narrowed it to the front cylinder - same cylinder with empty fuel filter.

I pulled carbs and cleaned. One coasting enricher was stuck, so I cleaned, sanded, and confirmed that it moved. Both diaphragms are intact and working well. I upped pilots to 42, turned 2.5 out on both, no change. Turned front cylinder out until pop went away mostly, but I ended up between 3.5 and 4 turns out. Even then, I still got some pretty poppy pop in first gear rolling off the throttle pulling in the driveway.

Like I said, maybe there is a float issue in the front carb? I didn't open the float chambers while cleaning carbs

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post #2 of 58 (permalink) Old 04-04-2014, 05:04 PM
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I am only going to address one thing on this, others will chime in on other issues (as well as this one I am sure)

your filter that stays empty (but fuel flows)... I suspect its got a big air bubble stuck in the filter.. remember, air will rise to the highest point it can (without lots of external forces, such as large volumes/pressures of air, or fuel).
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post #3 of 58 (permalink) Old 04-04-2014, 06:23 PM Thread Starter
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The fuel line is arced upwards, there's a section of hose that's higher than the petcock outlet and the filter... I'll swap the line with another one.

I looked at it after it sat for a bit, and it was half full. After starting the bike it immediately drained

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post #4 of 58 (permalink) Old 04-04-2014, 06:45 PM
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personally I would scrap the fuel filters until after you have the backfiring fixed.
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post #5 of 58 (permalink) Old 04-04-2014, 07:00 PM Thread Starter
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Will do. There was a nice little inline that came with the bike when I got it, so I'll pop that on. It's a bullet style, not the cheap huge conical one like I have on

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post #6 of 58 (permalink) Old 04-05-2014, 03:56 AM
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You knows that stock from the factory there aren't any fuel filters.

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post #7 of 58 (permalink) Old 04-05-2014, 06:56 AM Thread Starter
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There's junk in my filters already... If I can fit a filter under there I'm going to lol

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post #8 of 58 (permalink) Old 04-05-2014, 02:59 PM Thread Starter
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Got the popping removed, I can Rev high and let the throttle go and it cruised nice. It still pops on low revs but not overly concerning.

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post #9 of 58 (permalink) Old 04-05-2014, 03:10 PM
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good deal.. and flat spot gone too?
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post #10 of 58 (permalink) Old 04-05-2014, 03:20 PM Thread Starter
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No, flat spot still there. I would describe it as a power hesitation. I need bigger mains, since it cuts out pretty bad around 5500 under heavy throttle... Wonder if that'll help.

Since I'm 3.5 turns out on one carb, do you think I should up from 42 to 44 or 45,whichever is next up?

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