SU Carb Experts

[gira]

Guys,

 

Is there a way to tell if the carbs are worn out without some elaborate set up to tell if the shafts are leaking? I assume someone that knows what they're doing can sort of look at them, wiggle them some, and tell if they're going to work properly. I am mainly asking about shaft play. What is acceptable?

 

Thank you,

Greg

[Xnke]

Not really. Best way to tell is bolt them on the car, and hit the throttle shafts with a little carb cleaner, just like checking for a traditional vacuum leak.

 

The way I do it is just wiggle the shaft like you said-you should feel barely a perceptable movement-any play in them will introduce an air leak, but it's up to you to decide how worn is worn. For your needs, (SCCA ITS?) you're gonna want to either polish the shaft and have it plated back up to slightly oversize, and then just ream the bushings, or fit new bushings and turn the shaft down slightly. (Not enough to get you caught, anyway!)

 

Although you did buy my old SU's with 8mm throttle shafts, so I guess the smaller shaft diameter is OK-or maybe those were just "runnable cores".

[gira]

Nah, it's for a streetcar that needs to have a reliable idle.

 

G

[Miles]

http://www.ztherapy.com/

[Xnke]

For a reliable streeter, I would start by using a long chucking reamer ream both bushings in the carb body at the same time, or if I couldn't get a reamer long enough, I would user some aluminum foil wrapped around the shank of the reamer, slip it through the "near" side bushing, with foil wrapped to make it a snug fit, and then ream the "far" side bushing. Then, turn the carb body end for end and do the same thing. This will help keep the reamer aligned in the bushings, but it likely won't be perfect.

 

Ream the bushings to clean up, then hard chrome plate the shafts. If you have to go more than 0.012" on the plating, skip the plating and turn the shafts to 8mm, then press in a new 8mm bushing the the carb bodies and ream as per above to 8mm, to clean up. Any place that does hydraulic cylinders will know where to get the hard chrome done, and can finish the shafts back to 10mm (or whatever size you need them to be) easily.