running problem

[steven400/4]

my 400/4 runs ok unless i pull the throttle back fast if i do it just dies if i do it slow it picks up fine and if i put it in 4th gear and hold throttle at 5000 rpm the bike trys to go then backs off and trys to go and backs off just keeps doing that
 

[LesterPiglet]

Have your carbs been cleaned recently? Are you using stock air filter and exhaust. Is there crap in your fuel tank?

[steven400/4]

everythink is stock and new filters tank and exhaust

[LesterPiglet]

Has this just started happening or always been like that? You probably need to take your carbs off and give the jets and orifices a good clean.

[steven400/4]

been like it since it went on the road i,m just rebuilding some carbs for one of my other 400/4 looks like i,ll have to put them on this one 

[Spitfire]

Have you checked the points, ignition timing, advance and retard unit, plugs etc before focusing on the carbs ?

Cheers

Den

[Bitsa (Ralph Wright - RIP)]

Steve,
If I remember right when I restored a 400/4 mine acted like that and it turned out to be the o rings on the jets.
Might be the same for you.
Bitsa

[steven400/4]

waiting for a mate to come and check all that before i take the carbs off but still waiting for him 

[exvalvesetdabbler]

Fuel starvation or gross over fuelling. Does it smoke or whiff of petrol from the exhaust
At that rpm/throttle position the pilot jet would have little influence since it runs ok ? at smaller throttle openings.

Check the simple things first

filter gauze on fuel tap blocked
Tank breather blocked
choke flaps not fully open can also cause problems
float needles sticking/clogged up not just the valves but the float movement on its pivot pin
induction air leak around some rubber bit

Next thing would be float heights, main jet needle circlip position and main jet size 

[steven400/4]

thanks for that looks like the carbs are comming off then

[steven400/4]

right gents everythink i,ve been told to try i have everythink has been change,d for new and everythink in the carbs aswell put back on bike starts fine but its worse when you snap it open it dies and cuts out
ok up date just put some diffrent carbs on now the bike revs as it should but car,nt get the revs under 3000rpm even with the screw rite off the rod that open all the carbs at the same time

[LesterPiglet]

Have you synced the new carbs?
I would say the old ones still have some crap in them. You need to clean all the openings with a small guitar string and an airline.

[steven400/4]

not synced them but just put them on my 400/4 cafe racer and had the same problem cut out when snap,d open so i now know it is the carbs just got to work out how to get revs down with knew carbs