CT 70 choke help please.

Andrew T

New Member
Recently acquired a 71 CT 70, runs perfectly but only when the choke is up vertical and not in the open position.
I've read it could possibly be the pilot jet being partially or completely blocked but it revs out beautifully and strong, no issues with running.
And when it's in the open position it behaves like a choke should during a cold start.
Could it be possible for the choke assembly to have been re assembled at sometime with the lever re installed the wrong way, don't even know if this is possible never took one apart.
Any help or experience would be much appreciated thank you.


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Active Member
pilot jet only runs idle and about 1/8 throttle, then the main jet kicks in. It sounds like you have a lean condition when choke is open.
could be low compression
air leak
needle clip setting
wrong main jet size
running a "free flow" air cleaner

Andrew T

New Member
You're right Lukelaw,

First I raised the jet needle all the way up for more fuel mixture and it still stuttered at high revs but only needed to choke it half way now so it proves it was too lean.

Seems at some stage someone put in a new CT 70 carby kit which has a #60 main jet.

I've since realized mine has an ST 70 engine and the recommended main jet is a #65 so I went and got one and changed it over, revs real nice and crisp now but haven't had a chance to run it on the road as it's been pouring rain here where I am but I feel confident it should be an improvement.

Thank you Lukelaw, been a great help.

Andrew T

New Member
Problem solved, the #65 main jet and raised jet needle fixed the the problem of running only with the choke on, obviously it wasn't getting enough fuel as someone along the way used the wrong main jet.

Now it revs out and my first experience with how a proper 70 should ride.

At first I didn't want to touch a 52 year old classic but glad I did, it brings us closer together, ha ha.