Hi all!

I live in Colorado at 5,000ft in a very dry climate. I just bought a 2005 S40 with 3k miles on it. It's a great bike and in great shape, but I can tell it's not tuned properly because it has the backfiring issue as well as has some power loss at some rpm's and chugs a bit when changing gears. The previous owner drilled out the exhaust so there are 4 1/2 inch holes in the muffler, as well as put in a K&N drop in filter. The idle mix screw plug is also uncovered. When I got it the idle mix screw was turned in pretty far so I have been gradually loosening it and testing. I have the screw pretty far out now and the bike runs better but still backfires and I can tell it just isn't quite right yet. I have read conflicting information about adjustments for this altitude. I have read that a higher altitude needs a leaner tune, but a dryer climate needs a rich tune. I have both here so I am not sure where to go.

I would also like to know if there are any easy performance mods I should do for my situation. I have read about taking off the airbox door, and removing the snorkel thing under the seat but I don't want to go about hacking up the bike if that's not necessary/needed.

backfiring can be too lean, but it also can be too rich.
what happens is that leftover gas accumulates in the muff and just waits for a breath of fresh air to ignite.

So the 1st thing to do is eliminate the fresh air.  check for loose header bolts and air leaks all along the header and muff using a lit candle, the flame will blow around when you're close to a leak.

For a stock bike at your altitude, it's generally best to leave it stock.

You gotta K&N drop in and a drilled muff, both tend to push it leaner.

I wouldn't take out the snorkel or the door as that push it even leaner.

Tell us when it backfires as that's a clue as what to do.

How low is your idle set? With the closed throttle / decel pops, I find that when my idle is set a little higher it mediates most of my afterfires. I also notice that when my fuel tank is down to about 1/4 I tend to have more than normal (not sure why for me - with Raptor and vacuum tubes are plugged, cone filter & fish tail exhaust, but at a similar altitude 4500+ & dry)

If you can't get your bike tuned with the stock air filter....I wouldn't suggest going to a cone.  It will be harder to tune that to run well.

Dave

The cone filter does little (or nothing) on the Savage performance by itself.  The engine is horribly restrictive inside, and the CV carb isn't great for performance, and the engine is low compression with a very mild cam.  The muffler change to a DYNA and decent jetting is the best bang for your bucks.

The cone filter is mostly done by folks wanting the look...they want to get rid of the airbox and battery and make a big open space under the seat.  The stock air filter works well enough for the stock engine and carb.

Dave  

Dave wrote on 08/11/14 at 10:45:19:


Good to know! How much better would the Dyna muffler do for me? My stock muffler is already drilled out.

Dave wrote on 08/11/14 at 11:00:15:


Mine sounds pretty decent drilled out. I think I am going to order a few jet sizes today so I can experiment with them. Looks pretty easy to swap the jets out. Just drain the fuel from the carb, unscrew the screws and put the jets in right?

I wasn't really thinking earlier. A girl I work with's husband is a salesman at a Harley dealer. I am sure he can find me a Dyna pipe.

So it looks like to start off I need to install the Dyna muffler, do a 150 main jet and a 55 secondary, as well as do the 2 washers instead of the plastic spacer. Would that be a good starting point?