I've never had so much trouble with SUs before, please help!

[Bork Volvo]

I want to give everyone a sincere thank you for your ideas and thoughtful replies. Just to let you know, I have successfully resolved the issue with my SU HS6 carburetors and the 4,000RPM limit!

I had a bit of a meltdown this morning where I turned to my helper and said, "I hate this car." I was feeling so terribly defeated that I dismissed him for the day and started putting away my tools.

In my SU drawer, I found another set of authentic SU jets still in the box. A lightbulb went off; at this point, the jets were the only things that I hadn't revisited or switched during my entire campaign. The jets fitted to my car were purchased from a local British car specialist. Even though the jets were new and supposedly for SU HS6 carburetors, something in my gut told me to get rid of them.

I swapped them out for the SU jets from my inventory and my car suddenly would rev to the moon! An absolute night and day difference.

Again, thank you for your thoughtful replies and creative problem solving. Hopefully this saga can help somebody else with a similar issue!

[Moomoo]

Originally Posted by Bork Volvo

I want to give everyone a sincere thank you for your ideas and thoughtful replies. Just to let you know, I have successfully resolved the issue with my SU HS6 carburetors and the 4,000RPM limit!

I had a bit of a meltdown this morning where I turned to my helper and said, "I hate this car." I was feeling so terribly defeated that I dismissed him for the day and started putting away my tools.

In my SU drawer, I found another set of authentic SU jets still in the box. A lightbulb went off; at this point, the jets were the only things that I hadn't revisited or switched during my entire campaign. The jets fitted to my car were purchased from a local British car specialist. Even though the jets were new and supposedly for SU HS6 carburetors, something in my gut told me to get rid of them.

I swapped them out for the SU jets from my inventory and my car suddenly would rev to the moon! An absolute night and day difference.

Again, thank you for your thoughtful replies and creative problem solving. Hopefully this saga can help somebody else with a similar issue!

Great thread, didn’t understand all of it but enjoyed it.

Super outcome! 😄👍

[Ron Kwas]

Bork;

In order to help me (and presumably others interested and who offered troubleshooting help) understand exactly what it was on those carbs which did not play with your engine, I would like you to measure the unloaded length of the Dashpot Return Springs on the carbs which exhibited the Rev limiting issue (or, if you can make out any color-coding on them)...they should be 5 1/2" and Red...

If they are taller, or a different color, this probably means they were replaced with a spring with higher spring-constant, which were intended for carbs fitted to higher displacement engines (or for instance 2 carbs on a 3liter engine)...don't forget, these carbs are highly configurable, and while your rebuilder maybe thought they were doing something good by renewing them, by installing the wrong DRSs, they built in a Throttle limiting factor (and a bit of a trick and puzzle for you, and us!)...which on your engine meant that Dashpots never rose as high as they should have with WOT, effectively being a Throttle limiter... That would be the only answer and explanation to the issue I can think of, given the new info...

Cheers

Edit: Which also means that with the correct DRSs installed, those "problem carbs" will also work just fine!

Edit2: ...and as far as the jet being the cause, I can't believe this, as the 0.100" jets are the only ones which would fit our Metering Needles (starting at 0.099")...if it was a 0.090" jet, the MN would bind and never allow the Dashpot to fully close to the Venturi, and that must have been one of the first things we asked you to check for...

[Derek UK]

Great that you are now running OK. However, as Ron's Edit 2 says there is only one jet that works with the HS6. If you think there is something wrong with the jets you could send them to Joe Curto at British Superior in NY and ask him if they are normal and OK. Take them in for him to look at if you are really keen. He might be willing to chat if you give him a call.
Being care full not to bend the needle, offer the bad jets up to one of the pistons with it removed from the carb and see if there is any interference. The jets should go up flush with the piston.

[Splinelube]

Congratulations. You're a patient fella.

[Bork Volvo]

Originally Posted by Derek UK

Great that you are now running OK. However, as Ron's Edit 2 says there is only one jet that works with the HS6. If you think there is something wrong with the jets you could send them to Joe Curto at British Superior in NY and ask him if they are normal and OK. Take them in for him to look at if you are really keen. He might be willing to chat if you give him a call.
Being care full not to bend the needle, offer the bad jets up to one of the pistons with it removed from the carb and see if there is any interference. The jets should go up flush with the piston.

Joe Curto lives 262 miles from my house, NY is a big state, and I am on the other side of it. The problem jets are already in the bin and garbage day was yesterday.

[Bork Volvo]

Originally Posted by Ron Kwas

Bork;

In order to help me (and presumably others interested and who offered troubleshooting help) understand exactly what it was on those carbs which did not play with your engine, I would like you to measure the unloaded length of the Dashpot Return Springs on the carbs which exhibited the Rev limiting issue (or, if you can make out any color-coding on them)...they should be 5 1/2" and Red...

If they are taller, or a different color, this probably means they were replaced with a spring with higher spring-constant, which were intended for carbs fitted to higher displacement engines (or for instance 2 carbs on a 3liter engine)...don't forget, these carbs are highly configurable, and while your rebuilder maybe thought they were doing something good by renewing them, by installing the wrong DRSs, they built in a Throttle limiting factor (and a bit of a trick and puzzle for you, and us!)...which on your engine meant that Dashpots never rose as high as they should have with WOT, effectively being a Throttle limiter... That would be the only answer and explanation to the issue I can think of, given the new info...

Cheers

Edit: Which also means that with the correct DRSs installed, those "problem carbs" will also work just fine!

Edit2: ...and as far as the jet being the cause, I can't believe this, as the 0.100" jets are the only ones which would fit our Metering Needles (starting at 0.099")...if it was a 0.090" jet, the MN would bind and never allow the Dashpot to fully close to the Venturi, and that must have been one of the first things we asked you to check for...

My springs are red on the end and both of them are the correct length. I purchased these springs from VP Autoparts, part number 71816.

I spoke to the British car specialist who sold me the jets originally; he insists they were for a SU HS6 carburetor, but he mentioned may have been for a 1962-1964 Austin Healey 3000, which also used the HS6. The documentation that came with the jets he sold me were instructions for HS6 carburetors, along with a pair of NOS BC needles that I never used.

I noticed that the faulty jets were not color coded like the SU branded jets I installed (my current jets have either an orange or yellow band). They also looked subtly different than normal SU jets; while the orifice for the needle was brass, it was surrounded by an aluminum tube instead of being a one piece brass jet. The weird thing is that my KN and KD needles sat perfectly inside the problem jet. Laid flat on a table, they were the same dimensionally in terms of length of jet and the fuel supply line.

Although these problem jets appeared to be genuine SU to the casual observer, they were not. The instruction sheet I have said SU-111 in a corner. After doing a web search for that SKU, it corresponds to a kit offered by a company called Royze under their Karb-Tun-Kit line of products. Attached is a picture of a recent eBay listing for one such kit. Notice how similar the jet looks compared to the SU version; as I said earlier, my old jets were aluminum with a brass orifice, not all brass.

[Ron Kwas]

Bork;

Thanks for follow-up info to help us understand...!

WOW!...so incorrect Jets were indeed the culprit!...something else to watch for!...I have to wonder just by what mechanism they caused this...do I dare ask "Country of Origin" of these Jets?

Note to self: Check off "Learned something new today".

[Bork Volvo]

Originally Posted by Ron Kwas

Bork;

Thanks for follow-up info to help us understand...!

WOW!...so incorrect Jets were indeed the culprit!...something else to watch for!...I have to wonder just by what mechanism they caused this...do I dare ask "Country of Origin" of these Jets?

Note to self: Check off "Learned something new today".

Supposedly Royze was founded in 1952 and has made 100% of their products in the USA at their own facility. They are still in business today.

https://www.royzeinc.com

Browsing their website, it appears that many of their jets now look identical to SUs and are completely brass. Perhaps my example was an older production that was withdrawn for defects. Although I had a singular bad experience, I'm not going to condemn them completely. It looks like they have a wide array of products and I am sure they have many happy customers over the last 70 years.

[Ron Kwas]

Bork;

I hear what you're saying, but fact is that the two jets fit, but had some sort of strange issue which I would have dearly loved to fully understand...

Cheers