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Discussion Starter #1
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. :surprise: 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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When you put on the GB, did you put on the stock mufflers too, or run open after the GB?
 

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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?
 

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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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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)
 

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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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Discussion Starter #9
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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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.
 

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The fastest VN750 I've ridden and owned had full stock exhaust. No amount of jetting changes or tinkering has ever compensated enough for the loss of backpressure. This engine LIKES backpressure.
 

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There is no known way of getting more power out of the Vulcan 750 engine, and it does not need any more power. IF you could get more power out of it, it would put more stress on the engine and shorten it's life. If you need more power, get a bike that makes more power stock.
 

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There is no known way of getting more power out of the Vulcan 750 engine, and it does not need any more power. IF you could get more power out of it, it would put more stress on the engine and shorten it's life. If you need more power, get a bike that makes more power stock.
I'm not so sure. I did an earshave, and I'm open pipes after the GB. I rejetted from 38/132 to 40/143. I'm getting slightly better mpg this year vs last year (45.5 vs 44.1 average over several tanks).

My new jets are giving me 11% more fuel on the pilot and 17% more fuel on the mains. If my MPG rose, it must be more efficient. If it was all simply cosmetic, than my MPG should have dropped nearly 11% instead of rising 3%.

If it still runs well with 11-17% more fuel (and sputtered lean without rejetting), then it must be taking in more air than before. If it's taking in more air, it must be producing more power. Maybe not 17% more. I might be rich at WOT. But 5-10% more.

Unfortunately, no one has done a dyno run before and after on the same bike to prove it.

All I know is the extra fuel must be going somewhere, and it isn't going to low MPGs.
 

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The fastest VN750 I've ridden and owned had full stock exhaust. No amount of jetting changes or tinkering has ever compensated enough for the loss of backpressure. This engine LIKES backpressure.
It's not back pressure specifically, but the timing of the pulses out of the exhaust. Show me exhaust pipe diameter changes significantly, this ends and negative pulse back up the pipe. This negative pulse helps to scavenge through remaining exhaust out of the cylinder. The goats belly is part of the tuning for this.

The stock exhaust has a diameter change right at the exit of the goat's belly. Removing the mufflers puts a very large diameter change at the same location. The tuning of the exhaust pulses does not change with removing the mufflers. However, the back pressure is reduced significantly.

I didn't really notice a change from the back pressure, until I had also done an ear shave. That was when I noticed that putting the mufflers back on, resulted in it becoming too rich to run properly.

In reality, no engine in the world likes back pressure. It's all about pulse tuning in the exhaust. The less restriction you have in the exhaust, the better. The engine has to work to push the exhaust out of the engine, so you might as well make its job easy.
 
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