I have a 1992 XT400 Artesia,just a small bore XT600.The bike is missing badly with any throttle,but runs well with the choke on,also low speed running is fine.The secondary carb diaphram is ok,so I'm thinking the float level might be too low,I have no manual,not even an XT600 one,so could anyone tell me the foat level?

Sounds more like fuel SUPPLY is short. I would first check if the fuel cock flows freely, then by-pass the fuel pump or check the vacuum line actuating the fuel pump, the check if the float needle is not stuck.

------------------
Fred, XTZ660, Holland.

You could be right,but someone has been here before me,I think they may have lowered the float level to stop fuel leaking from the bowl because of a faulty gasket(unavailable of course) sealer has also been used which may be causing a blokage - I have also resorted to a sealer,bad move I think.I don't want to go back into the carbs again,so if I get the float level right this time,that's it for the float level.

There is two ways to measure this, just assuming for your carb it is the same as for the XT600:
1. Support the bike so that is vertical, on a flat surface. Jack up the front wheel so that the mating surface carb / bowl is horizontal. There should be a little hose connection on the bottom of the float bowl. Put on a plastic transparent hose. About 15 centimeters from the end you slip on the bowl you should put two lines on the hose, 6 mm apart. Other end of hose to be fixed temporarily upwards. Unscrew the little drain screw in the bowl, from the left side. Now fuel flows into the hose. Start bike and let run for 4 minutes, idle. Matching the upper line on the hose with the mating face bowl / carb the fuel level in the hose, being the same as in the bowl, should match the lowest line on the hose. Level may be not more than 2 mm lower than the lower line. The 6-8 mm is a XT600 measurement however.
2. Remove carb from bike. Remove bowl. Turn float upwards so that it rests on the needle. Measure distance from mating face to lower side of float. Fot the XT6 this should be 25 - 27 mm.

Also: check colour of spark plug, is it very white? Any air leakage somewhere in the inlet tracts? Any mods to the intake system?

Auke