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TEV - Transient Enrichment Valve (Read 739 times)
Serious Thumper

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TEV - Transient Enrichment Valve
07/14/12 at 20:38:36
The Transient Enrichment Valve (or TEV for short) is intended to provide a bit of extra fuel when you roll off the throttle at road speeds to coast down to a light, etc.   It's primary job is to control the burbles and blaps that occur naturally on a big single when the engine is winding down from speed.

People who do unbalanced modifications to their Savage and wind up with "excessive noises" of several different sorts have been grasping at "clipping the spring" TEV straws to try to fix what they did to themselves.  

Ditto with the ones whose bikes suddenly want to die off at every stop light because of their unbalanced modifications -- they want the TEV "add a washer" fiddles to magically come to their rescue.

Folks, there is no consistent TEV magic.

TEV modifications have a 50% success ratio at best, most get backed off by the people trying them as unsuccessful or counter-productive.  

There may be a bit of logic to this 50% as they are trying two completely ass-backwards things to try to help the things they did to themselves with their recent mods instead of moderating the mods that caused the issues in the first place.

What follows is the consensus from the TEV WARS and the 3 different TEV modification threads that exist in RSD.   Read the procedure and if you decide you must fiddle with your TEV follow the steps as listed so you can try to avoid the $70 plus in replacement parts that have been required by some to get their bikes back to working order after getting themselves "teverstrated"  (a painful form of TEV castration done with a sharp clipped spring end).

TEV modification steps:

1)   Write down all the thing you did to get into this mess and consider reversing some of them before going TEV snipe hunting.

2)    Having made an informed decision to go on a TEV hunt --- make sure your carb is clean & properly adjusted and your valves are properly adjusted and your petcock is working 100% correctly.   Don't have anything else muddying the water while you are chasing a TEV modification.   DON'T DO ANY OTHER MODS while working with your TEV  (changing anything else will overpower the effects of a TEV test and drive you crazy trying to figure it all out).

3)    With a clean cloth spread on the ground to catch any misc springs and bits that come out, use an impact driver to break the 3 phillips screws loose.  Replace these with hex head screws for any future forays (there will be more forays as TEV fiddles are 50% or less successful).

4)    Clean your TEV carefully, preserving the very fragile $70 diaphragm from any sort of carb cleaner induced damage.    

Be sure to rod out all the tiny passages feeding the TEV using the appropriate jet cleaning wire.  If it looks like crud was an issue, put your TEV back together after a complete cleaning and see if your issues are gone before proceeding with anything else.   Run this way for a week and record your various symptoms as your base line starting point.

5)    FIRST, the no-cost easily reversible mods.  Add a washer under the cover (behind the spring) to increase the spring tension.  Reassemble the TEV and run it for a week.  Record all effects on all symptoms on a piece of paper (record keeping is important as TEV changes affect several things, some go good, some go bad, some stay unchanged).   Keep a organized written list of symptoms across the top of the page and TEV mod specifics listed vertically so you make up an organized cause to effect grid.   Get this all doped out now, or you will be repeating tests later on because you didn't do it now.

You can try a second washer, but please realize you have likely restricted your TEV valve's linear motion too much in doing so.

6)    Order a new TEV spring and have it on hand.   Clip 10mm (or whatever lesser distance you want to try first) off of the sacrificial spring and reassemble your TEV.   Always put the clipped end against the cover, not towards the diaphragm.   Run it for a week and record the symptom changes.  Keep on clipping one increment at a time until you know you have gone too far, in stages, giving each one a week to show all the symptoms and let you record the effects as they come and go.

7)    Pull all your TEV mod stages of data together and study it, deciding if you have found any sort of sweet spot and actually have found a worthwhile improvement that hangs around with some regularity.  

Folks often complain that their "sweet spots" don't last very long, so don't feel individual if yours goes away on you too.    Or you can be one of the lucky ~20-30% that hit a sweet spot that stays with you.

8)    If you aren't one of the lucky ones and having TEV'd yourself to death now, consider backing off on one of the mods that got you into this situation in the first place.   Unbalanced mods DO NOT MAKE FOR MAXIMUM POWER, a proper balance of low resistance air filtration, correct rejetting of a clean well working carb, bigger/high compression piston, performance cam, head porting and a free flowing exhaust makes the best power.    Noise per se isn't power.  Power is power.


Here is the TEV thread that resides in RSD (the most modern one first).  Feel free to discuss TEV issues to death over in this thread.   This TECH SECTION feeder thread is locked to make sure you put your discussion in the right place which is RSD.

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« Last Edit: 07/15/12 at 10:20:39 by Oldfeller--FSO »  

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