More Power? - Page 2 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #11 of 14 (permalink) Old 05-22-2019, 09:27 PM
I'm a rider
 
One1's Avatar
 
Join Date: May 2014
Location: Signal Mountain, TN
Posts: 764
iTrader: (0)
 
Garage
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.


1981 KZ750
1988 Vulcan VN750 (red)
2005 Vulcan VN750 (silver)
(2) 1994 Vulcan VN750 (red)

Engineering solutions for the VN750 Community.
One1 is offline  
Sponsored Links
Advertisement
 
post #12 of 14 (permalink) Old 05-23-2019, 05:14 PM
Members who have donated towards server costs
 
Join Date: Nov 2007
Location: Chandler, Arizona
Posts: 2,850
iTrader: (0)
 
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 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
VN750Rider/Jerry is offline  
post #13 of 14 (permalink) Old 05-23-2019, 08:30 PM
Senior Member
 
Jason Pittenger's Avatar
 
Join Date: Apr 2018
Location: Northern Illinois (Not Chicago)
Posts: 239
iTrader: (0)
 
Garage
Quote:
Originally Posted by VN750Rider/Jerry View Post
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.


'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 #14 of 14 (permalink) Old 05-23-2019, 08:36 PM
Senior Member
 
Jason Pittenger's Avatar
 
Join Date: Apr 2018
Location: Northern Illinois (Not Chicago)
Posts: 239
iTrader: (0)
 
Garage
Quote:
Originally Posted by One1 View Post
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.


'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  
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Once registered, your User Name"cannot be changed". We can make exceptions within 7 days, but after that, it is set in stone.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome