Since you are new to the Savage/S40 LS650 world I would suggest taking a little time and doing the simple steps first to get a feel for how the engine responds to changes. For a new stock bike an adjustment of the pilot air adjusting screw to richen the low throttle range and eliminate the backfiring issues and smooth out the power delivery is the first step (drill & remove the brass cap covering of the pilot screw is necessary... see tech section for info), then swapping the stock muffler for a HD Dyna muffler of '04 or earlier vintage is a good follow-on. Those two simple changes will make a noticeable difference in smooth running, responsiveness and power.
Step 2. If you want more then you have to start changing things. Thats where you get into the Performance Carburetor, Performance Camshaft, and high flow exhaust system.
More Money = More Power-Perforamance Carburetor Kit: $399
-Performance Camshaft: $199 ( plus cam core exchange or $50 core charge)
-Performance Exhaust System: At least a Supertrapp or similar high flow muffler, or Jardine system. Removing the stock header with its restrictive 1.3" ID is necessary if you want full benefit of other changes. The Jardine system has a 1.5" ID header which is a good size. You can also make your own if so inclined...I did a 1.75" OD/1.6"ID pipe and added a high flow muffler which has worked great for me.
The engine was still at stock compression of 8.5:1 and the exhaust port just slightly opened on the outside and the engine produced 45 hp at the rear wheel. A stock engine has about 25 at the rear wheel.
Performance runs produced 0-60 mph times of 4.9 sec consistently. It could have done much better if I could have kept the front wheel near the pavement. 90% of the run was in 1st gear and hitting 60mph just after shifting to 2nd gear. Installing a clutchless shifting mechanism will also help improve times.
!/4 mile times were at 14.2 sec @ 90+.
Top speed to date was 105. Just did that once ... seemed to be a perfect engine day. Hitting 100+ several times with 95-97 mph routinely.
This is with a Veypor unit installed so the speeds and times are exact.Since then material has been removed from the head/cyl (0.040") to raise compression about a point to 9.5:1, and the exhaust ports have been significantly opened for better flow.
The engine was assembled and started but had an issue with oil leakage on the head ... seems I had some brain cells that were not functioning properly and left off the valve stem seals...................... the oil really runs through the valves when you do that
So a bit more work is needed to correct the stupid mistakes before it is ready for the road. Hopefully there is no damage as a result of my lapse.
I expect to see 50+ hp with the higher compression and exhaust flow.
An additional mod to the Performance Carburetor with the UFO from Thunder Products is in the works which may improve the low-midrange power and responsiveness....and you guys who have the UFO in your carb now thought the UFO was great already ? wait till this new mod comes out !!! UMM UMM, it is a good one and it is as easy to do as changing a pilot jet ... sort of ...
I makes tuning the low throttle range soooooooo simple ... stay tuned ... same Savage time ... same Savage channel