does my carbs needs to be tuned? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 42 (permalink) Old 10-17-2017, 03:24 PM Thread Starter
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Question does my carbs needs to be tuned?

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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post #2 of 42 (permalink) Old 10-17-2017, 05:08 PM
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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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post #3 of 42 (permalink) Old 10-17-2017, 05:12 PM
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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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post #4 of 42 (permalink) Old 10-17-2017, 06:09 PM Thread Starter
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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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post #5 of 42 (permalink) Old 10-17-2017, 11:42 PM Thread Starter
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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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post #6 of 42 (permalink) Old 10-18-2017, 12:07 AM
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Need to check the coasters.


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post #7 of 42 (permalink) Old 10-18-2017, 09:33 AM Thread Starter
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Quote:
Originally Posted by One1 View Post
Need to check the coasters.
what is that? sorry for my lack of knowledge
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post #8 of 42 (permalink) Old 10-18-2017, 10:26 AM
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Quote:
Originally Posted by eltiti21 View Post
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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post #9 of 42 (permalink) Old 10-18-2017, 11:09 AM
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the petcock has the following 3 positions on your year.
on
res
off

there is no 'rest' position. I am going to assume you meant off.

just helping out the rookie with terminology!

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post #10 of 42 (permalink) Old 10-18-2017, 02:06 PM Thread Starter
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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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