Problems with two up touring on my 250

[Onlyalittleexcess]

Since I got my old 1979 xs250 back on the road in November I have been throwing the good wife on the back and racking up a couple of hundred kms each Saturday or Sunday.
Whilst I acknowledge the limitations of the old girl ( bike ) we have had a blast getting around Perth and surrounds after a few years away from two wheels.
The bike cruised around 90-110kph without too many problems up until just recently.
Now when under load on the open road it gets to about 100kph and then starts to loose power and the speed drops right down until the power cuts back in again.
I had had this problem once before under load going up a steep hill, now it does it all the time on the freeway or open road.
Apart from this the bike runs very well. It can redline in lower gears and doesn't miss a beat. Cold starts are terrible but thankfully I live on a hill.
Points have just recently been changed along with plugs by the local bike shop.
Plugs when I removed them were sooty, not sure if any clues there?
Any advice greatly appreciated.

 

[drewpy]

running lean, check for cracks in inlets and not sure if you cleaned them carbs.

do you run a fuel filter?

 

[Onlyalittleexcess]

The carbs were supposedly cleaned etc at last service a month ago...perhaps not that well ??
No fuel filter.
Do you mean cracks between the air box and carbies?
Is there an straight forward adjustment to get the mixture richer?

 

[SpecialK]

Your plugs look quite good, if you were running lean they would be white and charred. I'd check your float height, its possible that when you are cruising at 100kph its gets starved for fuel because the floats are set to high.

 

[xschris]

Those look a little rich to be honest. The white parts should be clean and the tip a light gray.

 

[Onlyalittleexcess]

Many thanks guys , but now I am confused ... one lean, one rich and a float height issue
Wish I wasn't such a newbie and could test all the theories , just hate throwing it back to the shop when these things happen.
Mrs and I might have to go on a diet to keep the revs up

 

[drewpy]

easy check, just apply a bit of choke on the move and see if it helps.

 

[Onlyalittleexcess]

Thanks guys but it appears the problem has been solved.
I never touch the petcock as I don't get to Res and it stays on ON the whole time.
When I inadvertently checked the other day it was set to Pri
Not sure how it happened but makes good sense now as to why it was dying under load.
Set it back to ON and off we went...didn't miss a beat.

So the old girl ( bike ) lives to face another day.