I did an evaluation and modification of the TEV and I wanted to share the results with the forum.

The TEV provides more fuel when manifold vacuum is high, like when you chop the throttle to decelerate.  Under a high vacuum condition, our particular motorcycles have a tendency to backfire.  I'm sure everyone here is familiar with that little problem.  Adding more fuel during the high vacuum condition helps to eliminate or mitigate the backfire condition.  The TEV accomplishes this by closing off the #230 pilot airbleed jet located in the dome of the carburetor, just under the diaphragm.

During normal idling, cruising and acceleration conditions, the pilot and transition circuits receive air through two jets, the #230 pilot air bleed and the #45 air bleed.  Both are located in the dome of the carburetor.  Under high vacuum (deceleration) the TEV closes off the #230 pilot air bleed and the only air the low speed circuit receives is through the #45 air bleed.  This #45 air bleed is extremely small (only about .016").  I noticed that on older models there was only one pilot air bleed in the dome 9/2/22 error, my bad, there’s actually a 2.0 mm drilled passage, essentially a fixed orifice, so it had a #70 and the equivalent of a #200 (a #70) but those models still utilized a TEV.  So I got to thinking that in the old days they probably just shut off the pilot bleed air entirely.  I decided to try something like that on mine.  But need data to get things rolling so I hooked up a vacuum gage and snubber system to see what sort of numbers we are looking at.  

Here is a picture of the totally sanitary and professional installation of my vacuum gage.  BTW, any of you old timers remember Montgomery Ward?

 

I always try to get some good data before I make any changes, so I wanted to see exactly what sort ov vacuum this big single generated under various conditions.  I knew that vacuum would be high at idle, very high under hard deceleration, moderate at cruise, low under acceleration, and very low under WOT.  Here are the test numbers:

Idle: 6.5"Hg
Blipping throttle in neutral: 3" to 8"Hg
Moderate acceleration on surface streets: 3"Hg
Cruise on surface streets: 5"Hg
Moderate acceleration on the freeway: 2"Hg
Cruise on freeway: 4"Hg
WOT: 0.5 to 1.0"Hg (Petcock opens at 1.25"Hg.  Topic for another post)
Normal deceleration: 10"Hg
Hard deceleration: 15"Hg

Now that we know what sort of vacuum numbers we are dealing with, let's take a look at the TEV components and figure out exactly what sort of behavior we can expect based on its dimensions.

Here is a picture of the components that make up the valve assembly:

Very educational reading.  And heck yeah I 'member "Monkey Wards"!
Anyone remember White Front?
Or these, not sure if they were nationwide be we had 'em in San Diego:
FedMart
Alpha Beta (groceries)
Two Guys
Walker Scott
Pic 'n Save

In the picture of the blocked off jet I am using an old needle jet from some other Mikuni carb as a holder for the jet so I can file out the groove for the screw driver.  In actuality, the DynoJet looks pretty much exactly like the stock Mikuni #45 air bleed, except the jet hole was very large.  It was a perfect replacement.  Now, with the jet hole completely blocked off, the pilot and transition circuits will get ZERO bleed air under high vacuum conditions.

How did it work?  Great!  The engine performance remained the same.  Easy start up, good idle, great throttle response, good roll on power, good cruising power, no surging, no afterfire or backfiring while riding the bike under any conditions.  There was some very mild afterfire when blipping the throttle in neutral.  The test data I took with the vacuum gage explains that.  I will elaborate.

When blipping the throttle in neutral, the vacuum ranged from 3" to 8"Hg.  There isn't much force decelerating the engine, not like you would experience say coasting down a steep hill or downshifting to use engine breaking.  You have to really blip it hard even to get the 8"Hg.  So you don't really achieve a sufficient amount of vacuum to overcome the TEV spring force and shuttle the spool valve closed.  It doesn't close fully until you reach about 7.9"Hg.

If afterfire drives you nuts when blipping the throttle, you may want to shorten the TEV spring a bit.  Be prudent, don't take a lot off.  If you do, let everyone know how much you take off and how well it works.

In closing, my bike did not have much of an afterfire issue prior to fiddling around with the TEV.  The mods that I described in a prior post (see stock carb slide mods) pretty much had all the issues with this carb taken care of.  It wasn't a good test bed to determine correction of an afterfire issue because it didn't have that problem.  But the blocked jet mod shows that it can be done with no adverse effect on performance, and I'm certain it will mitigate afterfire.  I also learned a lot about the vacuum characteristics on this engine and was able to acquire good data to share with everyone.

You should be able to dramatically improve afterfire problems by reducing the size of, or completely plugging, the #45 air bleed.  If you want to take it a step further, you can shorten the TEV spring a bit.  Batman mentioned in a prior post that he shortened his spring in one-third coil increments, and also commented that if you go too far you can get back some spring pressure by filling in with a washer under the spring.

Hope this post is useful.  If you try it, let us all know how it goes.

DragBikeMike wrote on 04/15/18 at 20:10:59:


You can go back and fix that typo, and make the thread read correctly.  Once the discussion is over and folks post their results, this thread can be cleaned up and should be posted in the TECH SECTION (I will do that when the time comes).


DragBikeMike wrote on 04/15/18 at 14:49:22:


I really don't see much of a reason to "blip" the throttle on a Savage.  The engine has big heavy flywheels, a heavy crank, a heavy rotor....there is a lot of momentum in the engine.  Blipping the throttle quickly places the engine in a situation where the fuel/air mixture just isn't good as the engine is slowing down - and there is also a slightly lean condition that occurs in the instant you crack the throttle open.

The Savage engine would prefer that you "roll" on the throttle a bit slower.  Blipping the throttle and making a lot of noise may feel "bad ass", however a good running engine really doesn't need (or like) to be blipped.

DBM , Wow   , some how I missed this post,  and as usual you've  done a much better job of research . WELL DONE!

I just did this, I wound up filling my existing 45 jet with solder. I'll post the results but I had very little backfiring to begin with. Only once every so often on upshifts and sometimes a small poof at shutdown. I'm running a 155 main 55 pilot, air screw 1.5 turns out on a RYCA setup.

The drill press and scale spring test setup, obviously also very professional, is seriously clever problem solving. If I still had any, I'd award you a Gold Star.
You have an interesting collection of Stuff to fashion necessary solutions to problems. What you're calling a snubbed is that needle valve that you can adjust to very limited flow rates so a prolonged high vacuum will get to the gauge but short spikes will be attenuated?
I've been around since 05and seen the various skills of the people here. I'm really surprised at the widely varied experiences and skills I have seen. If a dealership would have a mechanic check this place out they could learn a lot. Right Now we have several relatively new guys who have some real problem solving skills. And then the Old guys who know what to do to get the carb jetted,how to feel for a little drop off on acceleration and how to interpret what it is doing and what to do to fix it. The Tev has been difficult for people. Well, for me. I'm more willing to just accept a bike that has a bit of performance and good manners left on the table.
If you're one of today's shining stars and I didn't mention you, mehh, we all know who you are. You guys should have been here when Hutch was pioneering the swap to chain.