I am guessing it is the Bystarter Valves (chokes).

I did read up the top that they are not sticking but for an engine to rev at 5k it needs to get a reasoanable amount of fuel and air.

If the carby rubbers are seated properly and the butterflies are pretty well closed that is about the only circuit that will give you enough of both.

regards
jon

what hapens when you give it some throttle?

what happens when you apply the choke?

5000rpm is quite a high idle and like jon says it needs plenty fuel or air for this to happen,5000rpm is also roughly where the bike idles with choke fully on.

is the plungers fully closed,try opening and closing the choke a few times just to see if it makes any difference.....just in case something is stuck open!!!!

if there definately is no vacuum leak then try adjusting the idle and see what happens.


william

its possible for the choke linkage to remain engaged even tho the lever arm has returned to an off position, chek the linkage returns and moves freely. When you put the carbs bak on tighten the 2 clamp screws on all the rubber intake seals,incase you hadnt before.. You said it idled ok for min then rev'd up,soundsl like it could be diaphram sticking &allowing main jet to fuel even tho they appear ok when pushed in by hand, maybe lube the plastic needle bodies with light oil to be sure.. Still think it might be slightly open butterflys, if you shine a torch from one side, the butterflys should totally seal or be very marginally open

MexicanGringo wrote:Still think it might be slightly open butterflys, if you shine a torch from one side, the butterflys should totally seal or be very marginally open

so i took the choke linkages apart and gave them a good clean, making sure to go easy on the plastic bits.
i also did the backing light trick ( a super tip) and the butterfly's to have them open just a fraction of a milimter, tighened everything up and IT WORKED!!

its not perfect, it still idles just above 2k RPMs and if i back the throttle (in the opposite direction) the revs will come down to a more respectable 1.5k RPM.

thanks again for all your help guys, looking forward to ripping up the roads of rural ireland with the Alpha 10's tomorrow