SQ4 only runs with choke

[kevin.mcdiarmid]

My friend has restored/rebuilt a 51 SQ4 and it only runs with the bi-starter out on the Solex, if he tries to push it in it dies right away, i tried it while trying to keep the engine running by reving it but i barely got it half way and it died
My newly restored 50 SQ runs great so we took my solex and put it on his bike.....same thing!!
he has double checked valve timing and ign timing and fuel source is an external tank and tried the bikes tank
anyone have any ideas?
thanks
Kevin
BC Canada

[paul.jameson]

Throw away the petrol in the tank and replace with new?

[Paul_Linden]

Air leak on the carb flange? Air leak in an inlet valve guide? Stale petrol? Engine not sufficiently warm before pushing choke in?

[kevin.mcdiarmid]

thanks for your ideas
new petrol in tank
bike well warmed up
carb flange ruled out by using my carb on his bike
real head scratcher

[paul.jameson]

How flat was the head when assembled? What are the cylinder head gaskets? What is the petrol flow like out of the petrol tap?

[kevin.mcdiarmid]

Hi Paul the head is the next thing as today when it was running we partially covered the carb intake and it ran while closing the choke so sounds like a lean issue
the fact that my carb on the bike didnt change things means the only thing left it the head

[paul.jameson]

Or a petrol tap which doesn't let enough fuel through. This can happen if the plunger doesn't come out far enough to clear the feed holes. Many years ago, on my Cammy, it was the cause of partial seizures when the bike was run at high throttle openings due to the mixture becoming too weak. At the time, the pistons in that engine were very well worn and in dire need of replacement so to have partial seizures was some achievement!

[nevhunter]

Has it got automatic ignition advance? IF it says retarded it won't want to go much off idle. Smallish air leaks have more effect at low revs Check fuel flow from tank rate again. Nev

[kevin.mcdiarmid]

2 fuel tanks tried and checked, its god good flow
Ign advance doesnt come in to the equation, its at idle
at idle with the choke out it runs pretty good, can warm it right up
as soon as the choke is started to be pushed in it dies,
im going to help him check for vacuum leaks on the weekend
thanks so much for scratching your heads
Kev

[paul.jameson]

Has the carb been stripped? If so, was a new gasket made for the flange with the 4 screws? Did it have the notch in it? If you don't know what I am talking about, let me know and I'll find a photo for you although there is probably one on here somewhere. The lack of the notch might well cause the problems you are having, but it is hard to understand why your carb worked on your bike but not on his.