Check the exhaust is fitted correctly and tight,all gaskets are in place if there are any, an air leak could cause this problem.
You could refit your original exhaust and see if problem is still there, check the carburettors are correctly set up and there are no blockages in the pilot jets or main jets.
Is the bike running ok , any misfiring or lack of power?
These bikes generally run rich with fuel to begin with, and even with a new exhaust they still don't need rejetting, although the carbs may appreciate being balanced.
I tried having my carbs rejetted years ago and the bike never ran correctly, so i had it all swapped back to normal and then it all ran okay again.
As Slappy suggested, i would check that everything has been fitted properly and that you have no air leaks, it's easier than you think to fit it slightly wrong.
When i bought my bike my mechanic noticed a bit of air blowing from the gasket area, so i bought new ones and when i was fitting them i found TWO sets of gaskets already in place.
All trace of the old gaskets need properly removing and the area where the gaskets sit need to be as clean as possible.
You can use a bit of grease to keep the new gaskets in place when fitting the exhaust.
More people are born because of alcohol than will ever die from it.
If you change your exhaust headers make sure the restrictor point of the new set is similar in overall opening size to the original set.
The original outlet measured: 35mm (narrowest point) to 43.5mm (widest point) externally at its most restricted point.
I’m not sure what the wall thickness is but I reckon it must be somewhere between 1.0mm and 2.00mm, my original pipes are still in good condition and I was loathe to saw them up to find out.
In any event the Motad replacement header system outlet pipe is has a clear open area of 1364sqm. Whereas the original outlet is restricted to somewhere between 962sqm and 1075sqm.
When I fitted the Motad headers the power band almost evaporated and a gas analyser showed it be running far too weak, this being supported by the plug colour.
A further test was done by a lazer temp gauge on the exhaust clamp bracket of both original and new pipes and this showed the exhaust gas temp had risen.
To solve the issue the Motad pipe was sleeved down first to 1075sqm which improved things no end, and finally down to 975sqm, which seemed to be better.
Plugs were checked and exhaust gas analysed and the results were as good as I could get them.
It is my understanding that if you don’t get the right back pressure the engine will run to weak and it is possible that you may end up damaging the exhaust valve edges and seats.
