Exhaust Port & Pipe mods for the XS650


I recently emailed Michael Morse in the US for some clues as to what exhaust port and pipe mods makes the XS650 perform better. Mike is a racer of some repute in the US and has some very definite ideas as to what is best for the XS650 when it comes to exhaust work. Of course this info is specific to my motor which will be a 750cc and is fitted with 44mm pipes and as Mike points out these mods will make it pull like a train to 8500RPM. Without these mods the larger diameter pipes will have a detrimental effect on low to mid range power.

My tracker fitted with 44mm high pipes

Firstly Mike recommends the use of Anti Reversion inserts where the pipe meets the head (see diagram 1)

        Diagram 1                               1.25" tube pressed to create A/R insert

These A-R inserts can be made from some 1 1/4" exhaust tubing and belled in a press then welded into the end of the pipe.
AR inserts: Prevent reversion during overlap and high gas speeds "fool" the exhaust port into thinking its better than it is.

In the head you can also make improvements by "D" porting the exhaust port, here's an ingenious way of doing it without having to weld up the port. Make a ring which fits into the port and then weld on a piece of flat strap which extends back into the port, this straightens the port giving much improved flow.

The only other option is to weld the port but this requires some heavy duty comittment and an experienced welder.

A restrictor of 1 5/8" at the end of the pipe is also recommended, this should be 6 - 10" long for best results.

Many thanks to Mike for this information and pictures of his own XS650 racer.

Mike is the owner of Vintage Brake and 650 Central.


Some time after I got this information from Mike Morse I contacted him again when the club racer project got off the ground wanting more information regarding what would be needed for the racer.

Mike, as usual, responded with the following diagram outlining what would work for our racer.

This was developed over many years and is tried and tested under racing conditions and we thank Mike for his generosity.

Cones made to Mikes specs.

End caps made and welded together.

Cleaned up ready for Jet Hot coating.

AR (anti reversion) cone design.

Pipes made by CES in Brisbane.

Fitted to the racer (not finished yet)