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MG Midget and Sprite Technical - Stuck throttle after head job

Upon completing a head job on my 77 1500 I found that the throttle is very stiff. The spring cannot close it. The carb was off the car for about one month. I checked to make sure that the cable was free in its housing. I did clean the outside of the carb with degreaser. The good news is that with the help from a friend pushing the throttle down with a screwdriver the car fired up first up first try. thoughts on the sticking throttle, do I need to take the carb off or can I get it to loosen up in place. Oh yea it is a ZS carb.
Thanks in advance for your help.
jt simmons

Disconect the cable and check each step individualy
Pedal assembly
Cable
Carb

You will find what is sticking.
Do not force any of the parts!
Certainly in a carb to many parts that can be damaged.
Onno K

I've experienced something similar, and have a couple of suggestions.

The ZS has a spring that fits around the throttle shaft right at the carb body. Make sure that's not sticking. Mine was... still not sure how, but it was binding a bit. I fiddled with it and modified the curve, and it freed up.

Also, if you have had the throttle plate off the shaft and back on, it may now be off-center and binding in the carb throat. What you need to do is to loosen the two throttle plate screws (carb off, natch), and make sure that the plate can freely close all the way. THEN tighten the screws, and again check for free movement from fully open to fully closed.

Have you verified that the stiff movement is at the throttle shaft?

Cheers, and good luck,

-:G:-
Gryf Ketcherside

The pedal and cable move freely. I did not have the throttle plate loose or off. The carb was removed and placed on the workbench for about a month then decreased with a spray before going back on yesterday. Do you think the degreaser spray de-lubed the shaft? I tried spraying silicone to no avail. I noticed the throttle was stiff prior to refitting on car, but thought that must be normal. I will have time to try any suggestions tomorrow. Thanks again.
Jim
jt simmons

WD40, drizzle it onto the linkages while moving them, keep spraying it until it frees up. I would guess the degreaser has stripped the lubrication.
WDT Corry

Interesting! So the trick here will be to isolate where the binding is occurring so you can deal with it specifically. I'd suggest removing the carb and rotating the plate/shaft while inspecting it very closely.

The shaft should rotate freely. As mentioned above, there are only a couple of things that's caused it to bind, in my experience. You should be able to see if the plate is scraping the inside of the throat, as this can make the throttle difficult to close... and this is what you've described. If it's not, you may need to actually remove the plate from the shaft... then check the shaft alone for free movement... and if it's still binding, remove the shaft for inspection.

Note too that the ZS carb, unlike the SUs, has a neoprene air seal around the throttle shaft where it enters the carb body. I can't see where that would be binding, but it would still bear inspection. If it's damaged, they're available and easy to replace.

Let us know how it goes. You've piqued my curiosity!

;-)

-:G:-
Gryf Ketcherside

This thread was discussed between 26/01/2012 and 27/01/2012

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