Intake Options - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 15 (permalink) Old 04-21-2019, 04:43 PM Thread Starter
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Lightbulb Intake Options

Hey guys, so i have been wondering about different options for intakes and fueling other then stock or the standard ear shave. I know some people have tried single carb conversions but they usually have balance problems. I thought of a few things like a single or dual mikuni hsr with a hypercharger, or maybe a dual barrel weber some how. The main problem with these is price. What i want is power with out breaking the bank. maybe velocity stacks, or ram air scoops of some sort. anyone who has messed with increasing the performance of our bikes let me know what i can do! and experience or ideas would be greatly appreciated, let me know what you guys think i can or should do.
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post #2 of 15 (permalink) Old 04-22-2019, 09:41 AM
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These carbs don't function well with open throats, so velocity stacks will just cause tuning problems.

Earshave works, don't think power gains will be worth re-inventing the wheel. May even get some power loss.

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post #3 of 15 (permalink) Old 04-22-2019, 12:27 PM Thread Starter
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These carbs don't function well with open throats, so velocity stacks will just cause tuning problems.

Earshave works, don't think power gains will be worth re-inventing the wheel. May even get some power loss.
What do you mean by them not working well with open throats? I dont mind fabbing something up but what i really want is to set my bike apart from the rest of the vn750s out there, something other then just the standard ear shave. but i also am looking to squeeze as much performance out of it as i can, one of my buddy's challenged me to race him (he drives a 2010 Honda Stateline 1300) I think i can beat him but i want to be sure.
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post #4 of 15 (permalink) Old 04-22-2019, 05:40 PM
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The theory is, that extra air flow over the ports in the carb throat causes them to run poorly. Same problem if a cheap replacement filter blocks those ports.

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post #5 of 15 (permalink) Old 04-23-2019, 03:22 AM
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There is really nothing you can do to give the Vulcan 750 more power, at least enough to notice. More noise may sound like more power, but it's usually less. I used to have a Goldwing, which came with 4 carburetors. One guy on the forum fabricated a manifold out of part of the original air intake plenum. and mounted a single 2 barrel Weber on it. He said it ran fine. There is no reason why it shouldn't, at least in theory. I have an old car with an inline six cylinder engine. It has an intake manifold with 6 runners, and a one barrel carb mounted right in the middle. It runs fine, It seems like it SHOULD be unbalanced, with the cylinders at the very ends getting less air/fuel mixture. There may be internal dampers inside the manifold to prevent that. But on a v-twin like the Vulcan, it should work perfectly. In fact it has worked perfectly. The Vulcan 800s only had one carb. The Vulcan 1500 Classic only had one carb, while the twin carb BUBF model was basically the same engine. My Sportster has one carb, and runs fine. So does my Honda Rebel 250 twin. I have long wondered why motorcycles required a carb for each cylinder. The problem with trying to do it homespun style is that on multicylinder bikes with one carb, the system was designed by engineers who knew what they were doing. Things are not always as simple as they look. That is why I have always left my Vulcan 750s alone. They run great, and not being an engineer, I see no reason to try and fix something that ain't broke. Yes, I do remove all the emissions crap, just out of principal, and to clean things up a bit. But that does not affect the way they run.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #6 of 15 (permalink) Old 04-23-2019, 07:58 PM
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Do the Ignition coil mod, getting a nice hot spark will help you as much as near anything else. Make sure your carbs are adjusted properly and are clean. Also if your running a stock petcock, turn it to prime, you starve for fuel at WOT otherwise.

My understanding of it, is that the ear shave, or straight pipes/ drag pipes only give you minimal power gains. and it will almost all be at the top end, you might even lose some low end power.

What you really want is to be able to vary the timing. Unfortunately VN750's have fixed timing and it would be a project to change it. The stock sensors would work for the crank angle but then you'd need a set of cam sensors, just a massive PITA to do.

Has anyone tried machining the head down to increase the compression? The old head I have looks like it has a bit of room to play with.
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post #7 of 15 (permalink) Old 04-23-2019, 08:34 PM Thread Starter
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It is rather difficult to increase power with almost no parts available for the vn750. but the engine still works on the same principals as all others so we should be able to increase power. I dont mind doing some work to get there, ive built a few engines before. If we could increase the bore a bit, increase compression, and increase air flow though the exhaust, intake system and heads themselves we could get some serious power out of it. I have a few ideas i want to try out i just want to know if they are possible.
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post #8 of 15 (permalink) Old 04-23-2019, 08:51 PM
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Has anyone tried machining the head down to increase the compression? The old head I have looks like it has a bit of room to play with.
I imagine it could be done, but the stock compression ratio is already 10.5 to 1, and even with that high of a ratio, it can run 87 octane without issues.

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post #9 of 15 (permalink) Old 04-24-2019, 02:41 PM
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i did lots of engine work from putting bigger sleeves and pistons,shaved heads twice,ported polished,different carbs on,never dyno the thing,est.about 20hp over.The easy part is shaving heads for more power
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post #10 of 15 (permalink) Old 04-24-2019, 06:03 PM
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While I see no practical reason to try and increase the power of a Vulcan 750, since there are much more powerful bikes out there, If you are doing it just for fun or a challenge, I get it. While I have never tried to modify a motorcycle engine, I am a hot rodder, and have built many high performance car engines, mostly old school small block Chevys. I currently have a 1993 Chevy S10 Pickup with a 450+ hp V8 engine in it that I built. The main reason I have never tried to hot rod a motorcycle engine is lack of parts, and their more complicated design. Seriously increasing the power output of an engine drastically increases the stress on all the parts. There are no high performance parts for the bottom end, transmission, and final drive of a motorcycle, so a hot rodded motorcycle engine would not likely last very long. When I built the engine for my truck, I started at the bottom, and built an entire engine out of mostly aftermarket parts that would handle the extra power. I had to change the transmission and rear end. It came with a 145 hp V6, and these parts would not hold up under 450 hp.

My interest in a single carb for the Vulcan 750 is to reduce complexity. I am well aware it would reduce power. But having one easily removeable carb that would never have to be synchronized would be worth it to me.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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