Engine and Engine Mods


My bike idles rough or stalls!

My Fuel Injected Vulcan used to idle smoothly but recently it's rougher and the engine even stalls occasionally.  When I roll off the throttle and come to a stop I never know whether I'll have a normal idle or it'll be fast or slow.

Do you have your annual maintenance checklist or owners manual handy?   If so add this item: "Clean throttle body throats".

The problem is a very thin ring of carbon that develops around the edge of the throttle butterfly. The hard black stuff is deposited little by little anytime you stop the engine and an intake valve is open. A bit of hydrocarbon and other noxious things flows up out of the cylinder, through the intake and (most of it) stops at the inside of the butterfly where suspended particles settle to form a ring.

Eventually that ring of carbon becomes large enough to block some of the air that passes the butterflies to provide part of the idle mixture.  Less air means less power so your idle becomes a little lumpy.  If that carbon ring is allowed to become larger it'll interfere with the closing of the butterfly so that it stops at some fairly random spot sometimes letting some air in at idle sometimes not.

The solution is simple.; Clean the carbon ring out of the throttle body throats using your choice of scrubber (old toothbrush, Q-Tip etc) and some carb/throttle body cleaner. Hold your throttle all the way open or use your throttle lock to do it while you scrub the ring away. Now, ladies and gentlemen, start your engines! And enjoy a nice smooth idle again. BTW, if you turned the idle up so the engine would run you'll probably find it's now idling way too fast.  Crank it back down to the recommended 950 (or whatever your owners manual recommends).

Check out Throttle Body Cleaning - Get Your Idle Back! for detailed instructions.

Last Updated: Saturday, October 06 2018 @ 09:33 AM PDT

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