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[thebullet]

Hi all,

Many of you would have seen my other thread about strange things when cold, this has all been narrowed down to the choke now.

I had some work done at a garage and i noticed it was put on so that it dosen't lock but just slides in and out like the water valve.

Anyway, when the choke is fully out, the car jitters about all over the place. The only way I can start off a drive without it doing this is only pulling out the choke slighly and managing the revs untill they will sit normally. If I did the same with the choke fully out, it hates it.

IfI do drive with it fully out and then push it in, it still goes mad untill I really get hight through the gears and it almost seems like the fuel has been cleared out of the carb then.

Tomorrow, I want to see if it is adjusted right.

What would this problem mean the choke is doing wrong? could the fast idle be out so I have to put too much choke to gain revs? the choke cable pulling too much so it is overfueling?

Sorry if people think I have repeated a thread, but I feel the last one was going off topic by myself.

Thanks again for your help, really appreciate it.

[Dan]

The choke control on an SU is two stage. The first 1/4" to 1/2" of movement of the control does nothing more than raise the idle speed, beyond that it starts to enrich the mixture. The cable should be installed so that the first 1/8" of movement of the control takes up the slack in the cable only. Then with the control at the point where it just starts to enrich the mixture you set the fast idle speed. On an HS this is the position where the cam just starts to move the jet, on an HIF there is an arrow marked on the choke cam that aligns with the fast idle screw when it's in the setting position.
Beyond that all the adjustment is automatic and governed by the choke cam and jet linkage, all the maths for that has been worked out in advance and there is nothing else you can adjust. You must fit a locking cable, either twist to lock or ratcheting. A sliding cable is no use, you need to be able to set a choke position. The enrichment is used to start the car, once it is running it might still need the higher idle speed in winter. It's perfectly fine to leave a little tickle of choke on in winter to make it run right because a little choke doesn't alter the mixture.
If it seems to be operating erratically, it's probably dirty. A little dirt in the mechanism plays havoc with the position of the stops against the cams and screws, and as the dirt moves about the relative position of everything changes. The carb mechanisms must be kept clean, use carb cleaner and scrub the operating faces and threads of the adjusting screws with a brass brush or a toothbrush. If that doesn't fix it, the cams and screws may be worn and need replacing.