Cookie,  

On the first page of this thread it says spring #35 not #31.  

edit . . .but i dont know if theyre using the same schematic or not.  

going by your break down image i assumed it would be spring #31, BUT. the link that was posted for ordering the new part shows a soring length of only 1.58" leading me to believe its spring #35 ??    

I plan on doing this mod as well so hopefully it will get cleared up as to which spring should be trimmed.

Tried replacing the stock spring with a somewhat weaker spring I found on eBay. (1.85" long, but thinner wire than the original spring.) Once the bike is warmed up, it now has no backfires or shutdown afterfires. The idle is slightly uneven. However, when I first started it, the idle was too low, and the bike would almost stall at stop signs.

I'm going to try riding it again, cold, with the idle speed turned up a bit and the idle mix screw turned in one turn, from 3 to 2 turns out. I think this method will eventually work on my bike, which is completely stock and running at sea level. If I can't get a decent cold idle with the idle mix screw, I will try a spring somewhere between the stock spring and the one in there now.

The backfiring was getting to be too much in group rides, where people kept saying they thought someone was shooting at them until they realized the sound was coming from my bike. (And I wasn't shooting at them.)

Well if the bike idles differently.....You have put a weak enough spring in so that the TEV is operating all the time.....not just during high vacuum.  This will probably make the bike run too rich.....as the TEV is supposed to only work when the throttle is closed abrubtly and the vacuum is really high and the mixture really lean.

I am expecting that your fuel mileage is going to be much worse.  The good news is....if this doesn't work out you know how to put it back where it was......or you can try and find a spring with tension somewhere between the two.

One question: If the best backfiring setting does result in the TEV being somewhat open at all throttle settings, is it likely to have a major impact when the throttle is fairly open? Or will it function somewhat like a too-large pilot jet and affect mainly idle and low speed?

Thanks!

David

Maybe so, but I have wracked my brains trying to find a cause for the backfiring. According to my brother, who bought the bike new, it backfired more when he got it than it does now, so it's possible there's a manufacturing tolerance (though it's not in the pilot jet, as I replaced that). The carb is clean, TEV is clean, no air leaks, stock everything except for Raptor petcock. All I have left to play with, I think, is the TEV.

I'll run it a couple days as is, if it's running boggy or gas mileage is awful, I'll try a slightly cut down stock spring, and if that fails, I guess I'll live with the backfiring. It's not bad if I'm riding solo, but when I ride with a group I'm frequently hitting the brakes and quickly backing off the throttle, as these guys ride a lot harder than I usually do!

Thanks for your advice and insights,
David

1970s technology, mostly, that has to meet 2000's EPA requirements. It's amazing they haven't updated the design to conform more to current conditions. I can see how a 1986 Savage would have problems, but mine is a 2007. Hopefully, though, I'll finally get it fixed.

If the TEV is affecting anything other than full throttle chop, decel... it's purpose is essentially defeated...
I'd be adjusting the slide,... which is also controlled by engine vacuum...

As it is,.. the two are interfering with each other...
JMHO...