apache snow-FSO wrote on 07/11/13 at 06:59:06:


Apache....I believe you are correct.

The O2 I had installed was an eye opener for me.  I had always assumed that when you closed the throttle and the slide or butterfly was closed  the high vacuum would pull lots of fuel and make the mixture rich - What I failed to understand was that the high vacuum is on the engine side of the slide or butterfly and the high vacuum does not reach the places where fuel flows (except for the idle circuit).  What I found with the O2 sensor is that the exhaust shows a lean fuel condition when the throttle is closed.  I believe at these lean conditions there is not an adequate amount of fuel or compression to allow the spark plug to ignite the mixture and the lean fuel/air mixture flows unburned out into the header pipe where it can be ignited either by the hot exhaust of by a flame that comes from the cylinder the next time the fuel/air mixture is ignited by the spark plug.  For those times where the fuel/air mixture is just on the border of being ignited by the spark plug.....that is when you get the quick burbling type noises that aren't very loud.  The big bangs occur when the mixture is not fired in the cylinder and builds up in the exhaust.....and when it does ignite there is a considerable amount of fuel and air that is ignited.

The TEV valve is supposed to allow a larger amount of fuel to flow when you shut off the throttle.  This may be a long shot....but I wonder if the use of gasoline with no ethanol would make a difference?  The jets in the TEV may be set up for gasoline that is not mixed with ethanol (1986 was the first years of the Savage).....and either increasing the TEV fuel jet or running pure gasoline could help?  Using the DYNA muffler instead of the stock exhaust combined with the ethanol may have just tipped the balance a little more and made the mixture too lean during deceleration. 

ADDENDUM:  There is a trend on this site to increase the pilot jet size to cut down the backfiring.  I believe that this does help as it allows more fuel to flow through the ilde circuit and provide more fuel to flow when the throttle is closed.  The probem I have with this is that it makes the engine too rich during normal operation at low throttle settings.

I got rid of 95% of the backfiring by changing the spring in the TEV to a shorter spring. The length of the stock spring has two negative effects on the valve's operation.  
Having measured the pocket that the spring resides in, I came to the following conclusions:
1. There was not much room for the diaphram to move or open during the high vacuum present at full throttle, thus limiting the enriching effect the valve is supposed to provide.
2. The stock spring was stronger than necessary and was closing the valve too abruptly during the low vacuum present at deceleration, thus the backfire.

Instead of cutting the stock spring, I chose to find a shorter one. I'm satisfied with the first spring I chose, a #90 spring I bought at Ace Hardware. Listed below are the dimensions of both springs:

                                  Stock         #90
Free length      1.400 in.         0.715 in.
Wire Diameter      0.032 in.         0.035 in.
Outside Diameter       0.483 in.         0.597 in.

My bike is a 2002 model with just under 4000 miles. I installed the #90 spring at around 2800 miles. The bike is stock with one exception: a previous owner drilled out the baffle. The bike is much more pleasant to ride, and I would recommend this modification before I changed anything else.

Anyone thinking of this mod should exercise caution.
I think you've done it the right way by swapping out the spring.
several had tried to mod the spring only to find out it didn't work for them.

WE HIGHLY RECOMMEND THAT YOU DON'T MOD THE STOCK SPRING

and 1st try to clean the carb and the TEV valve in particular before trying any mod.

I like the pops. I miss them when I ride other motorcycles.

Well I tried the shorter #90 spring from Ace this morning. It does help the pops a little but no more than a 55 pilot and it seems to make the idle a tad rich, just like the 55 pilot. So now I am back to the stock spring. The idle and cruise are the smoothest with a 52.5 pilot and a stock TEV spring but I do get a few pops.

This experiment only cost 40 cents to try.

Unless I discover some other magical cure I am living with it for now.

Why would I want to make it leaner on decel than it already is.

I believe that mod was for bikes that were dying when coming to a stop from a too rich condition.

found this..

http://www.vx800.net/man_eng/06_Fuel%20and%20lubrication%20system.pdf