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SU Carb Rebuild Question

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B

BWillis

Jedi Knight
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So I got my rebuild kits from Joe and started putting things back together tonight. While test fitting the new jets and needles I noticed that the needle would not slide down all the way into the bore. I loosened up the jet carrier about 1/4 turn and the needle moved freely. I decided to swap the carrier for one from another carb body. Good, thats now sorted.

Now I also have a problem with the jet sticking when the throttle is operated. I cand figure out how to fix this. Does anyone have any suggestions?

Thanks!
 
Ben -

If I understand your issues correctly, it sounds like a jet centering issue. This was just discussed here:

https://www.britishcarforum.com/bcforum/ubbthreads.php/ubb/showflat/Number/317299/fpart/1

What I do not understand is the jet sticking when the throttle is operated. I am certainly not an SU expert, but the jet does not move with throttle operation. It moves with choke operation. I am sure that the more knowledgeable members will help out with a reply.
 
Bent jet?

Believe it or not, the jet on my front carb had a slight bend, so the needle would stick part-way up/down. Piston would not drop when lifted.

Ben - does the piston hit the bridge with a "click" or "thunk" when you lift it with the lifting pin and let it drop?

Tom
 
It may be you're going beyond the "operational limit" of the choke linkage and getting it over center of the actuating lever. Rarely (if ever) would you get it to that point with all the linkage and cable in place, methinks.
 
Tom,

I'm talking about the jet. The needle piston has the lifting pin.

It may be that Im reaching the limit. But, on another set of carbs that I have I can rotate the lever this far without binding. It may not be an issue when I have them installed but I wanted to check with the experts! /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

Thanks!
 
Ben, there are a couple of things to look at. Make sure the jet slides freely in it's bearing through its entire range of travel, with all linkage disconnected. I've heard that the surface finish on some of the current jets is less than stellar, leading to some stickiness. A light polish may be in order.
Make sure the choke linkage is not applying any side load to the jet. With the jet linkage still unhooked, check the fit at various positions of the jet. If, when you are reaching maximum travel, the linkage is out of line with the attachment hole on the jet, adjust the linkage to fit correctly.
Jeff
 
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