It's just a slight change of plans. I'll circle back and revisit it at a later date. I've performed carb swaps before but it was either a single Stromberg to two SUs or two Strombergs to two SUs. Never ran into critical flow issues like here - but that's all part of the learning process isn't it?

Been messing with cars for over 40 years and I'm still learning new things.

 

I am curious if you know the history of the 2 SU HD8s. Were they from a triple setup, or some other car using a twin SU configuration?
UK parts catalogs show both Triple and Twin SU HD8s with UM needles, the production Triple SUs using Blue & Black P/N AUC 2107 springs, and the Production Twin SUs using Red & Green P/N AUC 4826 springs...
You may want to try the Red & Black springs before you go back to the ZSs? (We) will all sleep better, if we know the out come!!!! Haha

To test my results before and after modifications, I used a Drag Racing APP on a smart phone. Had a long flat freeway on ramp, just out of town that I could do 1/4 mile runs without merging. Recorded elapsed time and terminal speed; after, new distributor, triple manifold, 2 to 3 ZSs, 2.25" intake runners, and K&N filters. Springs and Needles didn't change, (except non-adjustable needles to adjustable). Used fixed Jets, and after 3 attempts, final setting (-.141" ) below flush.
Cut about 3 seconds off 1/4 mile times as reported in motor magazines road tests from the day.
Rgds
David

 

I do know the history: my brother owned a '71 E-type OTS and wanted to convert it to triple SUs. He found these three carbs and then found a complete carb/manifold assembly plus an air box. He let me have the three loose carbs since he sold the car afterward. They were missing parts so I was able to make two complete ones from the set. If I buy a few parts I can make the set-up triple again.

My aforementioned friend ran this two-carb set-up with the stock ZS manifold (which has 2" ports by the way) and he said it ran like a scalded dog. Of course, he'd had the engine breathed on. Joe Curto had instructed him which needles, etc. to use but my friend has since sold the car and couldn't remember what he used. He had so much money tied up in it he felt he had to move it on.

Don't worry, I'm not giving up on it - just putting it on the back burner for a while.

 

I saw on an E type YouTube video that carbs are often marked Front, Center, Rear ?? or something to that effect? Would that have any impact on what is going on? Just a thought.

 

On the triple set-up the carbs are all the same, only the float chamber orientation differs.

Took Old Scruffy out after reinstalling the Strombergs and she ran better (blanked off the decel valves and screwed the temp compensators shut). I still have the intermittent stutter - it sounds similar to hitting the rev limiter on a modern car but not consistent; it occurs around 4000 to 4500 RPM, mainly in second gear. Since this distributor has a vacuum retard unit (which is disconnected right now) I'm suspecting vacuum advance.

 

I still think that stutter could be interference from the leads impacting the electronic contact set up you have in the distributor. Try silicone leads, and suppressor caps.

 

Malcolm - I forgot to mention it on my last post but I did verify the plug leads are silicone. I replaced them not long ago.