Well..another day....another test ride.
The two different jets (1-120 and 1-127.5) ran OK but no real improvement in top end.
I've done a bit of research and discovered a few points. These things are likely obvious to the more experienced Big owners but a bit of interest to me still so I'll share.
Reading the service manual I discovered that the main jets for the SR41 were 120. When the SR42 (800 cc engine) was put in using the same frame and airbox as the SR41 the standard main jets used were 117.5.....so actually leaner.
This certainly supports Robs statement that when I put the 800 into the 750 frame (using the smaller airbox) that the bike would need smaller mains.
The other fact I discovered while searching the DR650 sites regarding the GSXR 1000 silencer was that the STANDARD main jets on the DR650 should be made SMALLER (leaner) if the GSXR silencer was used on the 650 with no other mods to the airbox or carbs. This supports what Bluesman has been saying all along that you have to have a large volume silencer for this bike. What complicates things for me here in the western US is that I MUST have a spark arrestor on the bike to ride anywhere off-road. The GSXR pipe supports the spark arrestor nicely so I'd really like to keep using it.
So now I have an engine that wants smaller mains and a silencer that wants smaller mains.
I have 125s in now and am thinking about going right back to standard jetting for a SR42...that being 117.5. I think I have those jets in the box.
I'll play with it tomorrow and see what happens.
So, even with you lot beating me over the head with information, it's still taken me over 3 years of Big ownership to learn stuff.