SU throttle shaft and bush dilemma - advice?

[Alec]

Similar to several other members having high idle and balancing problems, I went through all the checks to establish a cause to no avail. On a complete tear-down, we found a strange problem. The re-turn tab on the lever of the front carb (to which the return spring is attached) was very slightly bent and kept the throttle plate cracked - so thought problem solved. Tried again, now idle down to 1050, but carbs would not balance - the front carb doing most of the work.

The spray method did no show-up any leakage issues, but we concluded that the throttle plate must be hanging up in the bore somehow - this is what we found. The part of the body around the throttle shaft has broken away exposing the bush, and this rough edge seems to be causing the shaft/plate to hang up. I think the wear pattern on the body can be seen.

Do stock HS6 carbs as fitted new have brass bushes?

If no, then these carbs have been poorly re-bushed before and I am in for a challenge. The only solution I can see at the moment seems to have new bushes made with a concave profile to match the interior bore. If yes, how common is this problem
Ideas or advice please, Thanks

 

[Alec]

Sorry , could not add picture of the other side in the previous post, so have added it here. Thanks again

 

[trrdster2000]

Alex, don't think I have seen a carb that worn out, you may be flogging a dead horse. Lets see what some of the others have to say. I have a good set but you need to have someone near you to find a set, as shipping to Canada is very expensive.

Wayne

 

[Simmo]

Hi,
I'm all away in Australia and I use Joe Curto in New York for my Carburettor problems. He is the best and very reasonable in price. Its even worth the postage the other side of the world
Thats my two cents worth anyway
Here is the link

https://www.joecurto.com/index.htm

 

[TR3driver]

I don't believe they had bushes originally, certainly the earlier H6 did not.

I'm thinking you could just smooth away that rough edge and get by; but if not then new bushes all the way through and matched to the bore is probably the next step.

I forget the HS6 arrangement offhand, but I'm wondering if it might be possible to add some shims on the outside, to hold the plate better centered instead of letting it rub against side of the bore. I recently found that my H6 front throttle plate was hanging up on an almost invisible rough spot in the bore (not broken away as yours is), and adding a shim washer between the carb body & idle stop lever (so the shaft couldn't move forward under force from the linkage), plus re-centering the throttle plate solved the problem.

 

[Alec]

Thanks for the input everyone. I am fearful that the front carb may be a lost cause, and guess the worst case scenario is replacement, in which case Wayne we could be talking again.

Randall, I am leaning your way. It will be a challenge though - am considering tapping into the bushes with a suitable size tap (not sure what size yet maybe 3/8" UNC?) and driving out from the other end with a punch. If it works, then machine some new bushes and profile the one end to matching concave - indexing will be an issue when pressing in the bushes though. Your ideas of shims on the outside will be explored for sure, as I think they may be required even with news bushes, due to state of wear in the body

What do you think of minor refacing of the body with JB Weld?
Keep ideas coming and thanks again

 

[TR3driver]

Maybe I'm missing it, but those don't look all that bad to me. Mine certainly don't look much better.

I checked an old article by Tony Rhodes, his carbs were HS6 and there didn't appear to be a bushing before he put one in.

3/8" would be too large, most likely, that's the outside diameter of the standard bushing. 8mm might work, but it might be easier to just cut away the bushing with a reamer.

There isn't a lot to the profile, might be easier to just cut it after installing the bushings, rather than having to worry about alignment.

 

[Brinkerhoff]

Alec, I see darkened wear patterns that looks to me like the butterfly was installed off center , if anything. I've run just fine with carbs that looked no better than yours. Re-install the butterflies with the shafts installed leave the butterfly screws loose until they can close the throat off for the most part.

 

[dklawson]

I am glad others posted what I was going to say... it doesn't look that bad to me. However, pictures can be deceiving.

Are you saying that as shown in the first picture the witness marks on the throat from the butterfly are deep? I can't tell depth from the picture. IF that is what you are saying then you may have a problem getting the two carbs balanced and set properly at idle. JB weld on a very well prepared carb throat may help but ONLY if you take the other advice given above to make sure the newly installed butterfly is centered and does not rub against the JB weld. After all, JB Weld is softer than the metal you are applying it to and it would only be a VERY thin coat. It would easily be scraped or flaked off.

The throttle shafts should be 7mm in diameter (new). Therefore, if you use a tap to remove them you probably won't need anything larger than 5/16-24.

 

[titanic]

I am new to this forum, but would like to comment on the problem. It is typical of a botched rebushing of the carb body. When boring the carb body, the hole should not go all the way through. It will cause an air leak around the shaft and there is a slight possibility that the bushing could move inward and jam the throttle open. Also, all the h6 and hs6 carbs I have rebushed have had brass bushings from the factory. You could try to salvage it, but hs6 carb bodies are still plentifull and inexpensive on ebay.
Berry

 

[Alec]

Thanks again everyone, there is a lot of good info coming my way, particularly as first off I am trying to understand what caused the inner part of the vody to break away.
If the the HS6 came from the factory with brass bushes, then these are likely the originals. Can I then assume then Stock HS6's come stock with bushes?

In this case, is it possible that using a return spring that is too heavy (or too many springs), could create a side force that provides for the butterfly to gouge the area around the shaft? When I got the car 10 years ago there were two springs on this side, which I now assume was intended to overcome the bent tab found at the first go-around.

The cleshaft clearance at the moment is quite sloppy (guess at 0.010"+, so I doubt I can get away with not doing a repair.I already bought the std 5/16" shafts and bushes (never thinking to use the oversize shafts)

OK JB Weld is out. I will go out today and source a 8mm tap just in case though might this not be too small (0.316 vs 0.320")? and have a go at removing these bushes tomorrow, and also see if I can get someone with a lathe to make new bushes to suit the damaged body - experience trying to balance these carbs over the last 4 years has been fruitless, and I can't get over that this area of the body is the cause.

I'll report back.
Thanks again

 

[titanic]

Alec-I doubt that the bushings in the picture are from the factory. The original bushings are quite thin-walled and never go all the way through. The throttle shafts are 5/16" dia. Like I mentioned in the previous post, it may be easier to find another carb body than to salvage the one you have. Oversize shafts won't help as there would still be an air leak caused by drilling through the carb body. All of the hs6 carbs I have rebushed had bushings from the factory.
Berry

 

[dklawson]

I stand corrected on the shaft diameter.

 

[Alec]

A quick note to acknowledge the help;
Randall and Doug - there is a step of about approx 1/16" where the bush is recessed into the body and it looks like ample space for air to leak past the butterfly in the closed position. The witness marks evident are more severe in the shaft area. Based on comments, I may sacrifice this body in the repair attempt and do as you suggest and worry about the profile match after the bush is in. If the matching process destroys the body, then it is time to search out another body - was really hoping to get more drives before the snow flies

Brickerhoff - The butterfly could well have been off-centred and could be the cause to start the wear process of the body around the shaft. Per Randall, the shimming of this shaft to help maintain centre might be necessary

Titanic - It is only the forward shaft bore of the front carb where the small flange is missing and revealing the bush. You seem to confirm the notion that HS6 carbs come bushed from the factory. I noted through a search on BCF a comment that only the HS2 has the shaft run directly in the carb body and HS2/4/6 are bushed - don't know if that is fact though. Will try to measure the exisitng bushes tomorrow.
Thx all

 

[CJD]

Normally bushings are not too hard to find. Do a google search for local bearing supplies, and they should be able to set you up once you have punched those out. When you install, though, leave enough on the inside to file smooth with the throttle bore (unlike your predecessor!)

John

 

[dklawson]

The bushings are also available from APT. However, after installation they really need to be reamed "inline" to the correct diameter. This sounds like one of those situations where a call to Joe Curto would be in order.

 

[vivdownunder]

Throttle shaft wear can be greatly reduced with a drop of oil every now and then where the shaft enters the carby body. This also helps return to idle.

Shafts I've seen removed are nearly always bone dry.

 

[Alec]

Went over to a friends place (has Mill and Lathe). We assessed the stripped carbs for a couple of hours against the info received here, to decide best approach given the starting point was to tap and punch out the OEM bush.

It looks like this option will have to put aside, as there is indication that the brass bush is "captive" in the throttle shaft bores i.e. We drew a sharp scriber firmly across the bore surface and you could feel the difference in materials between the bush and the body material towards the outside edge, which means that the bush cannot be punched out. Also a visual through a magnifying glass seemed to confirm this - cleaned and took a picture (sorry it is not the best). It also looks like the rear carb is showing signs of surface cracks in the inner shaft bore area!! I am beginning to think that using too strong a spring with worn bores could be the problem

Looks like plan B to drill and ream is now the only way. Will get some new bushes and make a plan on Tues, as my friend had Chemo yesterday an it takes a few days......
Cheers

 

[Alec]

Just adding a nother picture to hopefully show that cracks are also now evident in the rear carb as well

 

[titanic]

Alec-Those black marks in the bore look more wear than a crack, but maybe it is just the picture. Strong return springs are sometimes used out of desperation to cure a shaft binding problem caused by misalignment of the 2 bores, which is usually caused by trying to drill the carb bodies in a drill press or using a hand drill.
I think the od of the bushes sold by Moss (and probably others) is .375" or 3/8". This may or may not be the same size as the factory bushings. I used to re-bush carbs using a piloted counter bore chucked in the head stock of a lathe and a center in the tailstock to support the opposite side bore. If your friend has a 3/8" or 13/32" piloted counter bore, you might try it. You might find some oil lite bushings locally or made that could be turned to required dia. You would still have to deal with problem of the air leak around the shaft caused by drilling into the venturi. Carefull filing of the new bush or making a fixture to hold the carb body in the lathe and machining the protruding bushing to match the carb bore is possible, but very time consuming. There are lot of hs6 carbs from elderly Volvos available that might work. I am using a pair on my TR6. This variation uses individual choke cables, but might work with the single cable linkage used on TR4As.
Good luck
Berry