Adding a Vacuum Manifold - Page 2 - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

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post #11 of 24 (permalink) Old 02-21-2020, 07:03 PM
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The coast enrichers are supposed to stop popping on decel. I haven't known anyone to modify them. They're behind the round'ish covers on the sides of the carbs, rubber diaphragm with a 'valve' and a spring. Also called Air Cutoff Valve or just Air Cut Valve, this is the quickest pic I could find: https://www.ebay.com/itm/85-VN700A-V...sAAOSwmOZbiK~K

Pretty sure mine were stuck or clogged when I first got it on the road, and it popped, some miles on seafoam and it quit. Have a suspicion this is the source of popping and not the air system. The repair manual says: 2-22 Fuel System 1) Check the inlet vacuum passage for the coasting enricher system, if backfiring occurs too often. 2) If the passage is clogged, blow it through with compressed air.

Tried looking at carb pics, best I could tell the vac port looks to be behind the throttle shaft. But you could check with a vac gauge or with carb removed see if the port comes out beyond the butterfly. Can blow or spray through the port also.

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 #12 of 24 (permalink) Old 02-22-2020, 06:42 PM
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Bike will not run without the coasting enricheners. My diaphragms were melted (ethanol) and I spent a small fortune to replace them.

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 #13 of 24 (permalink) Old 02-22-2020, 07:01 PM
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"This is my first bike, and I have yet to find another bike that I enjoy more all around (though the Triumph Legend TT is more fun, but not as comfortable living with). I don't want to replace it. After all the time and money I'm investing in this bike, I have no plans to risk damage! The bike may be worth $1000 or so on the market, but it's worth a whole lot more to me!
I understand the risks, and I appreciate the concerns. I plan to proceed with great caution"

Good idea. Too bad about the bike being wrecked. Glad you are ok. I have never crashed a street bike. If I did, and survived, I would not want the bike anymore. I bought one beater street bike (1980 Suzuki GS450L) that had obviously been dropped many times. Handlebars were bent, forks were bent, sidestand bracket was broke off, lots of scrapes and gouges. 36,000 miles and ran perfect. I turned it into a rat bike and rode it to work for almost 7 years. I got used to riding it with the bent bars and forks. But I never took it that seriously. I knew it was junk, and actually kind of liked that.

I spent $2700 for a low mileage 1997 Vulcan 750 several months ago to replace my bought new 2002 which finally bit the dust at 118,000 miles due to a cam chain failure.

I saw something about a tuxedo mod in your post. If there is one thing I would absolutely NOT recommend doing, that would be it, unless the engine is out, you have the left case cover off, and some distance from the bike. Doing it with the cover on the engine will fill your engine full of metal shavings, and do catastrophic damage. When I pull the cover off an engine, I go to extremes to keep dirt, even dust floating around in the air, from getting inside the engine. This is not just me. Ask ANY mechanic about the advisability of dumping ground up metal into an engine. When building/rebuilding/repairing an engine, keeping the inside spotlessly clean is probably the most important thing you can do.

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 #14 of 24 (permalink) Old 02-22-2020, 07:05 PM
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Quote:
Originally Posted by VN750Rider/Jerry View Post
Bike will not run without the coasting enricheners.
Sure it will, as long as the enricher circuit is closed. Might run with it left open, just richer.

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

Last edited by Spockster; 02-22-2020 at 07:08 PM.
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post #15 of 24 (permalink) Old 02-22-2020, 08:05 PM
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Quote:
Originally Posted by Spockster View Post
Sure it will, as long as the enricher circuit is closed. Might run with it left open, just richer.
If that's true, I guess there is no reason for me to spend another $150 to replace the diaphragms if I find mine melted again. That would be great.

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 online now  
post #16 of 24 (permalink) Old 02-22-2020, 08:19 PM
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Quote:
Originally Posted by VN750Rider/Jerry View Post
If that's true, I guess there is no reason for me to spend another $150 to replace the diaphragms if I find mine melted again. That would be great.
You can buy one for $12.

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 #17 of 24 (permalink) Old 02-23-2020, 11:06 PM
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Where? All the online parts places list them at $65 each.

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 online now  
post #18 of 24 (permalink) Old 02-24-2020, 12:28 AM
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Quote:
Originally Posted by VN750Rider/Jerry View Post
Bike will not run without the coasting enricheners.
Sure it will. Mine have been blocked the last 8k miles. The only effect is exhaust popping on decel.
Its not loud, it won't blow up the mufflers and it doesn't hurt the engine.

1989 VN750
Highway blaster

2006 Honda Rebel Diesel
100mpg, low and slow

1982 Mercedes 300D
Modified engine, 4-speed manual

Last edited by DenverDiesel; 02-24-2020 at 12:43 AM.
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post #19 of 24 (permalink) Old 02-24-2020, 12:32 AM
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Originally Posted by VN750Rider/Jerry View Post
Where? All the online parts places list them at $65 each.
Link in post #11. Priced lower than last time I saw them, they were around $24.

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 #20 of 24 (permalink) Old 02-24-2020, 02:31 PM Thread Starter
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I am referring to the reed valves that sit on the sides of the engine, that dump extra air into the exhaust during decel to burn off unburned fuel. I believe those operate using manifold vacuum. These are typically removed with an ear shave, and a plate is put in place where the reed valves used to sit. As I understand it, putting these plates in place stop the popping on decel.

When I did my ear shave last year, I left that system in place, because I like the popping on decel. I didn't notice any issues with the enriching diaphragms in my carb. It ran more or less the same as before the ear shave. Only more intake noise and slightly improved MPG. I did notice that running the idle screw slightly richer than optimal, got rid of the popping.



For the Tuxedo mod, I've got the cover off (needed to remove it anyways, to remove the cam chains). It will be modified off the bike, in a different building, in a different city and county . I actually didn't realize that people try to do this mod on bike. That doesn't sound like a good plan, for the reasons you outlined.


'89 VN750 Bought stock 4/12/18 @ 17805.9 miles $800. Wrecked once. 27454.5+ miles

Completed modifications:
Removed mufflers, straight pipes out of GB. 110/90 Front Tire. Pick-up coil mod. Shindengen MOSFET FH020AA r/r. 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 adv. Tuxedo Mod. Ignition coil mod.
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