Anyone using SUs take note [with pictures]

[lesingepsycho]

This evening I decided to swap in the new throttle shafts that I bought for my SUs. They had been on the car and driving <span style="font-style: italic">reasonably </span>well. They did however have a vacuum leak at the throttle shafts. I put my Weber back on in the meantime but have still never like the DGV as much as hot SUs.

So the short version is, after putting the micrometer to the shafts, old and new, the difference was astounding! The new shafts were the appropriate .248" whereas one spot on the old shaft was as worn down as .223"!!! That's a HUGE difference! No wonder it wouldn't idle smooth! After closer inspection there is a very noticeable ridge on the shaft from where it has been worn down so severely. See pic

Anyhow, I just thought I would throw this out there as something to consider for those of you struggling with your SUs. I'll tell you what, when I reached down and grabbed the linkage and it had lots of travel in the bore, I was pretty certain that they were way off. A little jiggle and maybe a little spray could tell you a whole lot.

I hope to get this new set of carbbies on tomorrow and then I'll really be able to see what kind of difference the throttle shafts make.

JACK

 

[Trevor Jessie]

Typical. I have a set on my bench right now that are worn worse than that.

 

[tdskip]

Anyone use the propane torch test to quickly confirm if you have air leaks at the throttle shafts?

 

[jvandyke]

HS2? I think I was told HS2s don't have any bushing in the carb body so the shaft is the only wear area as opposed to other SUs that are bushed and need to be rebushed too, or something like that. Hooray for HS2s I guess.

 

[Dug]

I know there will be some that say only the shafts wear, however the bodies can and do wear as well.
I’ve seen it a lot, of out of round holes over many years.

New shafts are such an improvement that it’s like renewing the bodies to an acceptable level operation.
The carburetor bodies will show signs of being out of round if measured with a snap gauge or hole gauge.
How bad it is depends of the mileage on the carburetors, how much grit was covering the engine area, dusty environments can add to the situation.

I’ve made throttle shafts for these cars, MGB, MGA and big Healey’s for years. Picking material that is 0.25 in diameter to start with and when cutting the slot in the shafts for fitment of the throttle plate keeping the slot narrower so it doesn’t extend into the carburetor body as much (more bearing surface). For fun measure the length (width) of the slot in a new shaft and compare that to the opening in the body. Sorry for the long bit but the bodies can and do wear.
Dug

 

[jvandyke]

I suspected, and still do, some wear on mine but they "looked" really good, no noticeable wear but I don't have anything accurate to measure them with. I put o-rings on the inside edge and covered the outside end with a smear of RTV. Took the o-rings back out as they interfered too much. I will get new shafts at some point. They are working very well as is for now though.