Hello fellow HD riders,

A few months ago I bought my first motorcycle (EVO 1340, built on a "legend" frame, shows the most resemblance to a softail heritage). Since I really want to know how this bike is built I decided to do some research and I ended up on this wonderful forum.
I have already found the answers to a few of my questions, but recently I started wondering about something new: my CV carburetor has a vacuum hose on the manifold side. On my carb this connection is closed. What I was wondering:

1. Where does it normally connect to,
2. Why does my bike run without this connection and
3. How come my vacxuum piston moves without a vacuum connection?

Also I noticed that when the engine is warm and I release the throttle (in neutral or with the clutch open) it sometimes takes a while for the engine to go back to idle. Could this be related to the vacuum hose? Or could this be a result of my bike not having the second gas cable (the one that actively closes the gas valve)?

I would appreciate any answers you can provide me with.

Cheers,

Patrick

 

Look up VOES or vacuum operated electric switch. It is a switch that when connected via electrical and vacuum hose (the hose you noticed) changes the advance curve of your ignition system timing. This helps prevents harmful engine pinging and helps with fuel economy and performance. Here is a great explanation on what it is and how it works:

http://www.wildwestcycle.com/f_voes.html

The carb piston/slide works on its own based on engine vacuum and it is not related to that hose you mentioned. Yes the voes and the slide work on vacuum, but they have nothing to do with each other. Again the slide moves based on engine vacuum, but that hose has nothing to do with it (other than making sure it is plugged if your not running a voes and it sounds like you are not). The slide moves to maintain a certain VELOCITY of air. Thus the name: CONSTANT VELOCITY (Harley CV carb). Here is the basics on how a CV carb works:

http://faq.ninja250.org/wiki/How_a_c...arbs_explained

Finally, a vacuum leak in either that hose or any part of your intake system (carb to manifold seal, manifold to head, or a leaky vacuum line) will cause the "slow to return to idle" condition. (A lean condition...). Also check your throttle cables, linkage, and your slide on the carb to make sure nothing is binding up. YD

 

Thanks for the information. As you correctly assumed I do not have a VOES on my motor cycle. The timing is simply done by the engine itself.
Anyway, I'll go and check my intake system for leaks.
Cheers!

 

Some ignition systems, including the stock H-D one, use a VOES, however some aftermarket systems don't. It seems fair to assume that your bike has one of the latter, otherwise it wouldn't run right.

 

Don't know about EVOs, but the vacuum hose on my 2001 CV goes to the vacuum opened fuel petcock.

I do not have a vacuum switch anywhere in my system that controls the timing. The only engine sensors are the manifold air pressure (MAP), the oil pressure switch, and the crankshaft position sensor.

 

Unless I am mistaken, there should not be a MAP sensor in the carburated EVO engine. The VOES should be a "T" off of the vacuume line going to the petcock and will be located between the cylinders just below the fuel tank. My 2001 Sportster had a vacuume activated petcock with a VOES, MAP sensor is usually used only in FI engines as it tells the computer what the pressure is in the intake manifold.

 

A slow return to idle is indicative of a lean condition. It can be caused by anything that causes a direct or indirect lean situation - improper carb adjustment / tune, dirty carburetor (partially or completely plugged jets, dirty needle), torn slide diaphram, air leaks (between carb and manifold or at the rubber intake boots between the manifold and the intake ports) ...

 

interesting...I know about the MAP sensors on the intake, but there is nothing in my 2000-2004 Dyna shop manuals or wiring diagrams about a vacuum operated switch on a normally aspirated engine...maybe older and newer models?