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Discussion Starter #1
hello, im basically new to the bike and bikes world to put it like that, i have some mechanic experience in cars not to much on bikes, so i buy this bike 03 vulcan 750 6.5k on the clock.

Bike was sitting for around 7 months, i cleaned all the fuel system, she is running back normal in my opinion. bike has K&N air filters on, no ears( stock air filter box) and has open pipes, i will be placing the middle muffler back on soon, i have run it a couple times, and spark plugs are running black like too much fuel, and she makes backfires when decelerating. she seen pulling fine, and go all the way through RPM normal. She idles at 1k with no misfiring or anything like that, sound good for me, but im a NOOB and need some adv before i start cursing her on longer distances than 2 block street.

Any help here? thanks
 

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black on the sparkplugs WOULD mean rich, but popping on decel means either one or both carbs are LEAN at idle (on decel)

You may benefit from adjusting the carb's idle mixture screw (small brass flathead screw inside the body of the carb) for the carb which feeds the side that id popping on decel.

in addition, I'd be surprised if your bike was running rich with pods and straightpipes unless it was rejetted. Did you add the pods and straightpipes, or did the bike come with them?
 

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I should say, too, that generally if you've got popping on decel, "loosening" (turning counterclockwise) those idle mixture screws should help. It takes some fiddling, but you'll figure out what you want eventually.

If you turn them too far out, make it richer, close the idle stop screw to compensate, you can get hard starts and an excessive amount of engine braking force. Turn them too far in, make it too lean, idle screw opened up more to compensate idle, wacky idle and popping on decel. Carbs are complex!
 

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Discussion Starter #4
thanks for that help mate, i will do so as soon after i get out of work, when i turn off the bike i always put the petcock on rest leave it idle for around 15 sec then turn it off, and i did check the plug now and they look light gray, lean, but i dont know if its bcus i shut it off that way, but i will give it a half turn on the screw on idle and the see whats going on, thanks
 

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Discussion Starter #5
i did try to turn out the screw and it backfire more, and bike doesnt run right, i close it up completely and did 2,5 same thing it looks to be working fine in 3 turns but still backfires when let go, if turn it 4 runs horrible and shakes, i will try to take out the plugs tomorrow and see if they are fine and working the 4 of them, i also let sitting the carbs on some seafoam for the night, tomorrow will drain it and try to run it again and see, bike was sitting for around 7 month but when i pull the carbs out they were super clean.
 

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what is that? sorry for my lack of knowledge
Check out the "Vulcan slang for newcomers" link in my signature for a jump-start on the lingo around here. :)

The coasters are little metal squarish plates that are used to plug the holes in the side of your engine after removing the evap reclamation system. A leak around the edge of one would affect engine performance.
 

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Discussion Starter #10
thanks for the info, and yes i check the two plugs on the side of each head and there is no leak on them, and in reference to the petcock, yes i put it on the off direction, looking to the rear of the bike, i will take out the plugs today to inspect they are working fine, also drain the seafoam, and try to run it again and see.
i know i read it before but in case of cars when they backfire is because is running rich or is out of timing, i still don't think that making explosions and trowing blue flames out of the exhaust is a lean condition. but you guys are the expert, i'm just a rookie. i will also check the description of THORN. thanks
 

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The coasters purpose is to stop the deceleration issues. They can be leaking so inspect better than just a quick visual glance. Missing an issue will cause a big headache you can avoid.
 

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Discussion Starter #12
alright i will take them apart and check them better, they supposed to be blocked right, because mines are, and it shouldn't be sucking air correct.
 

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How to get rid of the Pops and Backfires
Jun 28 2011, 7:50 PM EDT
Is your VN750 popping or backfiring? You already adjusted the air fuel mixture screws several times, checked for exhaust leaks, but still can't get the popping to go away? you might try Marbeling or installing coasters.

We will talk about Marbeling first.
Marbeling is just as it sounds. You will block off the Air Valve Switch located under the gas tank, just in front of the battery box (16126 on microfiche http://www.ronayers.com/Fiche/TypeID/26/Type/Motorcycle/MakeID/3/Make/Kawasaki/YearID/34/Year/1993/ModelID/4293/Model/Vulcan_750/GroupID/135832/Group/Air_Filter(1_2)) . You will need to "Shooter" marbles (or anything that will fit into the hoses to block the air flow.
What to do:
Remove the hoses on the two reed valves
install marbles into the hoses
reattatch the hoses

Now we will talk about Coastering
Coastering does the same thing as Marbeling, but is a lot more permanent and adds a cleaner look.
What you will need:
Coasters (you can find them on eBay or build your own)
Reed valve Gaskets (qty 2)

what you do:

remove the coasters, and the whole air valve switch to include hoses
Cap off the vacuum line on the right carb
remove the stock reed valves
install coaster plate where the reed valves were
go ride..

How to get rid of the Pops and Backfires - The Kawasaki Vulcan VN750 Bible
 

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Discussion Starter #15
my reed valves are block already, i will check for air leak on them, and the other part mention ont he picture, i will need to put the carbs out again to check those, whats the bad thing of running the engine backfiring when dec?
 

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Discussion Starter #16
coaster are not leaking, and bike run horrible now after the seafoam and 2, 2.5, 3, 3.5 or 4 turn screw just will idle but if you accelerate it it will bog and shut off, i take carbs out, jets are clean and good, but the tuning screw from the front cylinder is missing the little spring inside, will this affect or create my issue? now where can i get one?
 

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Discussion Starter #17
well i just found out that one pilot screw is missing the spring washer and the rubber, and the other one is missing the washer and rubber, i already order them OEM Kawasaki, they arrived on monday, i also check the coasting enricher and the back cylinder looks like peeling inside but not holes, and the front one (the one with issues) is missing a little rubber between the cap and the base like a vacuum seal, i created one with a piece of rubber and patience (a lot), i will be waiting on monday for the kit to arrive and install everything back let see if i dont have to burn down that bike lol
 

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Discussion Starter #18
parts arrived, install them all already, time to start the bike, to much way to much fuel, even with the jets close carbs are getting floored, gas are coming out from exhaust, carbs breather lines even through the intake pods, what i did wrong? some inputs here?
quick note i vacuum the petcock myself before turn in on the bike just to have the carb with fuel! maybe to much? will open the gas cap and see
 

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Sounds like a stuck float, or float height set too high.
 

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Discussion Starter #20
issue fix, took the carbs out again the needle from the incoming fuel was stuck open. with all the parts on the carbs new bike rides a bit smooth. but still back firing on front cylinder when dec, way less now but still does,
 
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