Scooterotica

Thought I'd got the jetting sorted and had got used to a fair amount of light throttle 4 stroking but I now have a problem if I run flat out in 4th for more than a few seconds. At 65mph GPS its pulling 6500rpm and seems happy as. But if I sit like that for much more than 10-15 seconds I get a problem when I come off the throttle. It won't take any part throttle opening just dying unless I give it wide open throttle. If I pull the clutch I can rev it with big openings but anything upto 50% sees it dying. Usually after a while it comes back.

I have a Mugello 186 v3 Dellorto 26 and clubman. Also got an MB fsdtflow tap and get the problem with full tank or low level. Keep trying to get mixture screw adjustment right but don't seem to be able to find a sweet spot.

Any ideas what's causing the part throttle to go off after a fast run and is it linked to the poor part throttle/4 stroking?

Are you using a filter? Full side panel?

You need to find if its a weak issue or a rich issue. Get the bike to the problem scenario again and turn the choke on but dont let the engine die. If the problem gets better its a weak issue if the problem gets worse its too rich. find out if its weak or rich first before you start adjusting.
Does it feel like its flooding or does the throttle feel very "light" when you come off the power?

How old is your carb could be needle and/or atomiser worn , had same symptoms on my ts.

Should have said I am running full panels and a foam filter on rubber elbow.

Needle and atomiser are new as I tried different ones originally. Just going to go and try the choke idea.

Just been out. Ran at 65mph for no more than 10 seconds. As soon as I came off the throttle it wanted to die and would only pull with wide open throttle. When stationary with clutch in it would only rev on full throttle but would pick up much better with the choke on....after 5 minutes if trying to run slowly it came back to normal.

So it seems like it's running too lean. Is it worth moving the needle up or down a notch or two?

Sounds a bit like it could be emptying the float bowl quicker than it can fill up causing it to run very lean after running for a few seconds of using a reasonable amount of fuel. What size float valve is in the carb and also are you sure you have no air getting in your fuel pipe. Crap fuel pipe can let air in and cause a vapour lock which will give the same effect.