From what I saw when I was in there.......there is little reason to put in bigger valves as the exhaust ports are very limited in what can be done.  There is a weird square hump that protrudes down into the exhuast port, and it is the bottom of the valve spring pocket.

You can open up the ring at the exit of the exhaust port, clean up the castings a bit in the ports, and button everything up.

I don't konw of anyone that makes a "hot" cam for this bike - the 3 available cam grinds are all increasing stages of "mildness".  The Stage 1 cam is what I installed and it runs great and does provide a power boost.  The Stage 2 cam is a bit hotter but still not a race cam and is very streetable.  The Stage 3 cam is between the Stage 1 and Stage 2.

Do your valves, add a cam, put in a Wiseco, change the carb to a Mikuni VM36, add a free flowing exhaust.....and you have all the motor that the clutch, chassis and brakes can handle.  

DR650 available cam profiles listed on the WebCam site are considerably higher than what we have now, but then the DR exhaust ports a MUCH nicer that ours.  Valve sizes are the same.  This is for the 90-95 models.

Lift:  .390/.380
Duration @ 0.050":  248/248

Lift:  .417/.405
Duration @ 0.050":  254/254

****************************************************
Numbers for the LS650

CAMSHAFT                           VALVE LIFT IN/EX                          DURATION @ .050

Stock camshaft                       .254/.244                                          224
Webcam std.                          .256/.256                                          226
Stage 1                                      .264/.264                                                 239
Stage 2                                      .274/.274                                                 248
Stage 3                                      .273/.273                                                 238

Effects of duration:
220-235  =>  Low End Torque
235-250  =>  Midrange Torque
260 +       =>  Top End Power

My engine has a Stage 1 cam, Wiseco 95mm, Mikuni VM36....and it easily revs over 6500.  My Trailtech Vapor claimed that once I did 7,200 rpm.

I found that my stock carb had a flat spot as you are describing, and the cure for me was to raise the slide needle a bit.  I had removed the white spacer and installed 3 of the metal washers.  I tried bumping up the pilot jet to cure the lean spot....but it did not help.  I had an oxygen sensor and meter installed, and the trick was to remove one of the washers to allow the needle to be raised, then I dropped the pilot jet back down to a #50.  It then ran great with a #50 pilot, #150 main and 2 washers on the needle instead of the white spacer.

mpescatori wrote on 08/08/13 at 04:55:21:


The valves themselves...yes, leave as is; unless the engine has a good bit of mileage on it, and if so, then a good basic valve job to insure proper sealing is all that is needed.
I do like to clean up the exhaust ports, but thats just me.  The crocked path and the exit ring that Suzuki deliberately designed to make this a low power engine just really bothers me.  I think they simply did not want another 650 single engine to interfere with the DR's role in their lineup.
The intake ports don't need any work, they are good as is.
If you want to get picky about though there is one thing that can be done that is considered to be helpful in improving air flow, and that is to polish the inside corner just under the valve seats.  As the air flows in through the intake ports, it turns upward toward the valves, and it is the inside corner of that path which is polished.  Along with & part of that path is the bottom edge of the valve seat.  If that edge is not smooth with the aluminum of the port wall, then mechanical smoothing of it will remove that small "speed bump" from the air pathway and should result in better flow.

When doing head work I use "touch" as a guide to what needs to be smoothed.  There are the basics, like doing the inside corners, but from there I feel my way through and if I feel something in the way then it is removed or smoothed.  These are the small things that interfere with flow; the big things, like the outer ring, just need to go.
It's like on a fighter aircraft; they originally had standard raised rivets until it was discovered that flush rivets reduced drag and allowed the aircraft to perform better.  Airflow is airflow.

I'm thinking about smoothing out the exhaust port for some time. But I want to keep the stock header. Would that do any good or would it even do harm?

Dave wrote on 08/08/13 at 17:53:53:

Dave you need to get rid of the stock header. It will sound so much better. That was my first mod and noticed more power.

very interesting information here, i have alot to think about