RPMs vary at idle - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 12-09-2012, 08:24 PM   #1 (permalink)
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Default RPMs vary at idle

Just bought this 2002 Honda Shadow 600. Cleaned the carb and installed a new K&N air filter and new plugs. It runs a whole lot better now.

However, all that work did not cure one problem. The RPMs will vary every couple seconds while at idle. It rides and accelerates just fine.

Any ideas? I'd hate to take it to a shop for something simple and have them charge me a bunch of money, just to say "sucker" behind my back as I walk out the door.
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Old 12-09-2012, 08:55 PM   #2 (permalink)
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How much variation are we talking about here? Minor dips and bumps are reasonably normal especially if the bike is cold, but considering there's no tach on that bike it's probably not so minor if it's enough to notice...
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Old 12-09-2012, 09:10 PM   #3 (permalink)
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It is a V-Twin.Smothness at Idle isnt its strong Point
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Old 12-09-2012, 11:17 PM   #4 (permalink)
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Quote:
Originally Posted by lugnutz View Post
Just bought this 2002 Honda Shadow 600. Cleaned the carb and installed a new K&N air filter and new plugs. It runs a whole lot better now.

However, all that work did not cure one problem. The RPMs will vary every couple seconds while at idle. It rides and accelerates just fine.

Any ideas? I'd hate to take it to a shop for something simple and have them charge me a bunch of money, just to say "sucker" behind my back as I walk out the door.
You may have a small intake leak or need to richen up the idle mixture a tab, did you set your mixture srew when you where done with the cleaning and the install of the carb? also check the vacuum hose that runs from the auto fuel petcock to the rear cyclinder for a nice tight fit and no cracking in the hose.
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Old 12-10-2012, 05:04 PM   #5 (permalink)
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Quote:
Originally Posted by ZackDaniels View Post
How much variation are we talking about here? Minor dips and bumps are reasonably normal especially if the bike is cold, but considering there's no tach on that bike it's probably not so minor if it's enough to notice...
I'd estimate variation is 200 - 300 RPMs and it cycles every 2 to 3 seconds . . . mmmmmMMMMMMmmmmmmMMMMMMmmmmmmmMMMMMM
mmmmmMMMMMMmmmmmmmmMMMMMMMMmmmmm (humm along for a full sensory experience LOL!)
I've owned many bikes and have not experienced this before. I'd guess it has something to do with the carburetor mixture.


Quote:
Originally Posted by Scrapdog2grand View Post
You may have a small intake leak or need to richen up the idle mixture a tab, did you set your mixture srew when you where done with the cleaning and the install of the carb? also check the vacuum hose that runs from the auto fuel petcock to the rear cyclinder for a nice tight fit and no cracking in the hose.
Thanks for the tip! I'll definately check that stuff out. The bike is 10 years old and a vacuum leak might cause it. Good idea.
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Old 12-10-2012, 11:28 PM   #6 (permalink)
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That sounds somewhat normal for a bike that's been sitting for a bit. Double check your hoses and what not on the carb you just cleaned out. Be sure the breathers and what not are not clogged up... then ride it. Having purchased nothing but used bikes, I will say they tend to run a lot smoother after a heavy week of running following a garage stored past. I'm not mechanically inclined enough to say exactly why, but I imagine it's just clearing crap out of the various lines and lubricating things needing lubricated.
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Old 12-11-2012, 01:48 PM   #7 (permalink)
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Agree with Zack and check all your lines for leaks. Get a vacuum guage they are cheap enuf and take a few reading. The guage will find any leaks in the system!!
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