Stromberg Adapter Plates - Federal v UK Spec

[terryp]

Russ
Thanks for the post. All the original set up is gone, I did try it for a week, but it was horrible.

My question - is using a modified federal adapter block, any worse than using a UK spec pair of adapter blocks and link pipe?

Thanks
Terry

[CBUEB1771]

Terry,
Years ago I worked with a very experienced engine designer. I had just acquired a set of the UK/European spec inlet adapters with the balance tube between them. I asked this engine designer to look at them and he felt that the area for flow in the UK/European balance tube was just enough to alleviate the cylinder filling imbalance problem. The equivalent area for flow in the US version is small in comparison and therefore it is a less effective solution. I would use the UK/European version. I did this for a while before I converted to a Weber head. I was happy with the performance of the UK/European inlet adapters. I'll answer the obvious question. I don't really prefer Webers over the Strombergs with UK/European inlet adapters. For real-world driving conditions the constant depression carburetors (SU or Stromberg) produce good low-speed torque and smooth transition to large throttle openings.

[terryp]

Russ
Thanks for that, what do you think the imbalance Problem would cause. The car does seem to run ok, the only issue is that I have never been able to obtain an even slow idle.
Cheers
Terry

[CBUEB1771]

Terry,
The balance tube should reduce roughness a bit, probably most noticeable at idle when the effect of the flywheel is minimized. The balance tube will also yield a bit more torque and power. How much I don't know. The telling thing to me is that every MG, Triumph, four cylinder Austin Healy, etc. has a balance tube in the inlet manifold and therefore there was/is wide acceptance that there is a reason to put it there.

[gus]

An even slow idle is probably carb tuning or vacuum leak

Strombergs hate vacuum leaks, any vacuum leak.

after looking for external vacuum leaks the top culprits are

main diaphragm

throttle shaft wear

throttle bypass valve diaphragm [little bolt on dealy next to throttle shaft, bypasses throttle at very high vacuum, for emissi90ns reasons, when rotten prevents throttling down]

[69S4]

I've never been able to get a 'slow even idle' with mine and I'm not even sure that Lotus managed it. There's a reference in MW's Twin Cam Engine book to the UK Stromberg's exhaust note as being 'splashy as it hunts' and 'not a regular beat as with Webers or Dellortos'.

Gus is right when he says the Strombergs are really sensitive to air leaks and I don't suppose that situation is improved these days with the carbs in various stages of wear and the potential for multiple other leaks, particularly via the vacuum take off. I've never had much of a problem with holes in the diaphragms and didn't notice much of a change when I replaced the throttle shafts / seals some years ago but the main 'O' rings have been a constant problem. Mismount them somehow, even by a fraction and the idle is all over the place. And it's very easy to get a poor seal. If you do the engine certainly hunts up and down on idle.

I don't have the throttle bypass capsules on my carbs. Were these a US only thing?

[terryp]

I don't have the throttle bypass capsules on my carbs. Were these a US only thing?

I think so Stuart, although they seem to be on quite a few UK cars. I managed to get some new ones.
To be fair I am comparing my tickover to my G4 that has Webers so probably hyper critical.