• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

SU- Can the throttle shafts be sealed or bushed?

Share this page

58Custom

58Custom

Jedi Warrior
Offline
Well, I fired up the 1275 yesterday after the refresh and set about with my first personal encounter with the SUs. I have a lot of experience with fixed venturii carbs like Holleys, Carters and Autolites, but the SUs are new to me. I do have a couple of manuals DL'ed from the internets.

With the engine running I used a tube to listen for vacuum leaks around the carbs and manifolds and noticed that the throttle shafts were sucking air. On a Holley I would first replace the teflon seals, then resort to bushings if the wear in the throttle plate is extreme. But looking at the factory manual and the SU tuning manual I don't see any seals in the exploded diagrams.

Do SUs have throttle shaft seals? What do you guys do with leaking SU throttle shafts?
 
Hi, Tom -

Only way to do it is to re-bush. Takes a special knack and a proper reaming tool. Most of us send the bodies off to Joe Curto, or someone specializing in the process.

Mickey
 
Agree, Joe is reasonable and does excellent work. He did mine. Sometimes all that is needed is new or oversize shafts.
 
The carb bodies usually do not wear, but the shafts certainly do. You can see it if you pull out the shaft, a deep ridge all around it. New shafts are reasonable and available at better Brit parts suppliers.
 
If you only have shaft wear, new shafts are the cure. If it's to a point where the body is impinged upon, bushes are available, as are oversize shafts. But as said above: line boring of the body will be required. If you're used to the "funny" (to us LBC guys) carbs you're half-way there. The ONLY source for proper quality parts is Joe Curto, tho.
 
Tom,
Sure you will find more wear on the brass shafts and less in the bodies. But in most cases the bushing holes in the bodies will be elongated just enough at 12 o’clock / 6 o’clock that they will need to be bushed. Sometimes the oversize shafts are not even big enough to true up the bodies when the carbs have “a lot” of wear.
You will be able to “roughly” tell how a new shaft “might fit” by pulling the old shaft out, flip it around and place it back into the body at a point where the shaft isn’t worn to check it full diameter to the carbs body.
Another check before ordering shafts is to take the letter “F” drill (0.257 diameter) from an A-Z index set and try inserting it shank first into the carb bodies. This will tell you if you already have oversize shafts from a past life. You may wish to insert a ¼” drill bit into the bodies (again shank first)to check the fit for standard shaft “feel”. Good quality drill bits (not harbor freight) will be on size to 0.001 under on the shank, the shafts bought from Moss will be 0.002 and sometimes up to 0.003 under the standard fraction size of 0.250.
This will let you test the waters of what you “might need” to think about when repairing or sending the bodies into be repaired.
"dug"
 
:thumbsup:
 
HS2s, (What you have on your 1275) is a little different animal than the HS4s ( MGB) and above carbs. The HS2's throttle shafts ride directly on the aluminum of the carb body and doesn't have the brass bushings like the rest of the HS series carbs, and actually this turns out to be a good thing. 99% of the time throttle shaft leaks on HS2s come from wear on the shaft not the shaft hole in the carb body, aluminum shaft bore rarely ever wears like the HS4's brass bushings do, so refitting with a standard shaft will fix almost all HS2 throttle shaft leaks. Hope this helps.
 
Down here in Johannesburg

I don't know what happened to my previous post but here is a repeat. About 5 years ago the 1500 midget was idling like a dog, no amount of amateur tuning could rectify the situation. I took it to a specialist as advised above and with a new this and a rebush there, plus needle alignment, absolute magic. This was its first SU overhaul I did after about 19 years of ownership. The SU is a very low maintenance carb so do yourself a favour get the whole thing done professionally and enjoy hassle free motoring.

In preparation for the Spridget tour in South Africa I have done 3 by 50 mile runs and I am averaging 33 mpg and I haven't touched the carbs for about 5 years.
 
Ok,
Now I'm interested....I thought 1500's had a Stromberg 150-CD4T carb? Did other countries put SU's on them?? I'd love to know.
"dug"
 
The UK spec 1500's certainly had SU's.
 
Re: SU- Can the throttle shafts be sealed or bushe

Hi Dug,
Down here in Johannesburg -My 1500 Midget is from the UK I shipped it out in 1984. It has twin SU's and I put a K&N filter on. Attached is a picture of the engine bay, you can see the twin SUs and the K&N filter.
 

Attachments

  • 11470.jpg
    11470.jpg
    87 KB · Views: 160
Re: SU- Can the throttle shafts be sealed or bushe

Very cool,
I would think that to be the ideal conversion to ditch the Stromberg for. Thank you for sharing that SU's were used on late models (75+) out of the US market. Learned something!!
 
Re: SU- Can the throttle shafts be sealed or bushe

any usa model converted to Twin Carbs needed a notch cut out of the wheel well to make it fit - any that I have seen that is
 
Re: SU- Can the throttle shafts be sealed or bushe

Yes, as JP says... something to do with LHD vs RHD configuration of the engine bay, as I remember.
 
Back
Top