TR4/4A TR4A Strombergs or SU's?

[karls59tr]

I know that there are differing opinions on whether Strombergs are more problematic than SU's. I wonder when the chngeover was from Strom's to SU's on the TR4? What was the reason for the switch back then? I'm more familiar with SU's having rebuilt a few but less knowledgable about Strom's. I fired up the 4A project car with Stroms and got a fair bit of black smoke and the engine would only idle with the choke pulled out. Car has been sitting for years so the carbs should probably be gone thru. I do have a good set of SU's that I could put on instead. Any opinions on that? Also...were the TR4A Strombergs the same as the TR6 units? I know of many TR6 drivers that have converted to SU's out of frustration with the Strombergs so I'm wondering if I would be further ahead installing the SU's?

 

[Geo Hahn]

It's my understanding that the back & forth from SU to Stromberg to SU on the TR4s & 4As was more about patents & licensing issues than performance.

I have one car of each and do not find one any better or worse than the other but then the TR4s had a simpler ZS that adjusts more like an SU (jet nut) compared to the later versions on the TR6.

 

[TR3driver]

The rights to the SU design were acquired by one of Triumphs' competitors, so the ZS carb was specifically designed to side-step the SU patents.

In general, I entirely agree that they are about the same as far as reliability, ease of service, etc. But one has to be careful to compare apples to apples, as the emissions versions of both types were much worse than the non-emission versions. The later emission SUs had all kinds of crazy things, including temperature-sensitive needle positioners and ball bearings in the domes.

Personally, I would focus on finding the problem rather than just swapping parts. I know several people that were convinced their "emissions" ZS carbs were the problem (mostly because they didn't understand them). Over $1000 later, they discovered that the engine didn't run any better with new SU carbs ... the problem had been somewhere else entirely.

"Have to keep the choke on" plus "blows black smoke" ... the black smoke is caused by keeping the choke on. You need to find out why it can't burn a normal mixture (likely poor ignition, could be no compression, etc).

 

[glemon]

Agree with Randall, will add that I ran a 4A with Strombergs as my daily driver for years, once I rebuilt the motor and carbs (and a lot of other things) it ran great and was very reliable. Started from below zero to over 100 degrees, ran very smooth, and also got good MPG, I could get 30 plus MPG highway if I drove with a light foot.

I think the Strombergs got a bad rap because most of them are on 68 and later cars with all sorts or valves and compensators that most people (including myself) are not really sure how to adjust or test and don't want to mess with.

They work on the same principle as SUs, and the main difference is the rubber diaphragm instead of the piston, they will run like crap if the rubber is torn, but the diaphragms last a long time as long as you don't monkey them up taking them apart or putting them back together.

I like the older Strombergs so much I put them on my TR250, runs great with them.