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Carbs and Fuel System
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post #1 of 14 (permalink) Old 05-19-2019, 05:50 PM Thread Starter
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More Power?

I bought my bike with Vance & Hines pipes on it. It was pretty loud so I put the goat back on. I didn't notice any change in power at the time. This weekend I put the V&H pipes back on to see if they were as loud as I remembered (they are). What I didn't expect was how much more torque I got. When I twisted the throttle it thew me back in my seat because I wasn't expecting it. So here's my question. Is it possible that the prior owner did something to the carb to make it run better on those pipes?
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post #2 of 14 (permalink) Old 05-19-2019, 09:43 PM
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When you put on the GB, did you put on the stock mufflers too, or run open after the GB?


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
22490.0+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
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post #3 of 14 (permalink) Old 05-19-2019, 11:00 PM Thread Starter
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Goat out. V&H exhaust from the manifold to the tail.
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post #4 of 14 (permalink) Old 05-19-2019, 11:55 PM
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Quote:
Originally Posted by T-Bone View Post
It was pretty loud so I put the goat back on.
Did you also attach the stock mufflers to the goat when you did this?


'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
22490.0+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
post #5 of 14 (permalink) Old 05-20-2019, 02:33 AM
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I beleave When you take the gb off it alters the back pressure and most people compensate for this by increasing the carb jet size so yes the last owner probably rejetted it I am not sure why but UK bikes use bigger jets than us bikes probably something to do with your emission laws in the states
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post #6 of 14 (permalink) Old 05-20-2019, 09:32 AM
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I would guess the jets have been changed. Are the pipes near the heads discolored at all? What color are the plugs? (should only need to look at two)

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #7 of 14 (permalink) Old 05-20-2019, 10:51 AM Thread Starter
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Yes. Stock pipes, goat, and stock mufflers were re-installed.
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post #8 of 14 (permalink) Old 05-20-2019, 07:56 PM
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In my experience, there wasn't much difference between mufflers + GB and no mufflers (but still with GB) when I had the stock intake.

After the ear shave and rejet (but still with GB), putting the mufflers on made it run terribly rich and poorly.

I too would suspect he rejetted for the new pipes. Try running with GB and no mufflers (yes, loud) to see where that puts you. Its a 10 min mod, but it should offer a bit less restriction and be about halfway between GB + mufflers and VH, and it's worth the time to gain the knowledge.

If you decide to stick with GB + mufflers, I'd suggest 38 pilots and either 135 or MAYBE 138 mains. I ran 38/132 (stock) without issue, but the bike is tuned lean from the factory.
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'89 Vulcan 750 Bought 4/12/18 @ 17805.9 miles $800
Purchased stock. Wrecked once
22490.0+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB
110/90 Front Tire
Pick-up coil re-gapped to .020"
Compufire 55402 r/r series regulator
USB Outlet + Voltmeter
Repainted Metallic Blue w/ new tank bages
Ear Shave (wo/ coasters) 40/140 NO shims 45MPG
MCCT conversion

Planned modifications:
Custom LED turn signals
Windshield
Highway Pegs
(Possible) ignition advance
Jason Pittenger is offline  
post #9 of 14 (permalink) Old 05-20-2019, 11:01 PM Thread Starter
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More gold than blue, but some blue. I'll run it with these pipes for a little while report back on the plugs and exhaust pipes. Since I just put them on I can't draw any conclusions.
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post #10 of 14 (permalink) Old 05-21-2019, 12:57 AM
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Quote:
Originally Posted by T-Bone View Post
More gold than blue, but some blue. I'll run it with these pipes for a little while report back on the plugs and exhaust pipes. Since I just put them on I can't draw any conclusions.
It may still have stock jets. Wouldn't be the first time someone skipped doing that.

Keep an eye on the coolant temp, a sign of running lean.

Sometimes just the right level of lean can make more power, but it flirts with engine damage.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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