Rover V8 - CD175 Stromberg’s running rich.

[R0vers]

Having just rebuilt the old rover V8, I took it down to the MOT and she passed everything else, but failed on the emissions – the CO2 reading should have been under 3.5%, but the reading mine came out with was 7.5%.

I took the tops of each carb and cleaned the dampers out and took the needles out and refitted. One of the brass shoulders on the needles was sitting slightly proud, so I turned the adjuster anticlockwise to lower it slightly. The Haynes manual says to have the shoulder in line with the seat of the piston, which I’ve done.

I’ve checked the choke, which is off and the air filter is new. Apart from the smell of running rich, she is running sweetly – but need some advice on what I do next?

I’m reluctant to keep going back to the MOT station each time I make an adjustment and ask them to check the readings again.

I stopped by a local classic car specialist this morning asking if it was something they would look at, but they said I need to find a rolling road who has more specialist equipment….

I know that running too lean can cause damage, but is it OK to run it around being too rich?

[Quagmire]

Might be worth investing in a wideband oxygen sensor, they aren't massively expensive anymore, then you can check what is going on quite accurately yourself.

Only downside is that it means taking the exhaust off and welding in a boss for sensor.

According to the AFR/CO table stickied on this section of the forum your 7.5% CO is roughly equivalent to an AFR in the low 12's or high 11's.

Only problem with too much fuel is that it cleans the oil off the bores and will generally soot things up.

[DaveEFI]

With Stromergs, the jet shoulders should be aligned as a starting point. The carbs then balance for flow, and any mixture adjustment carried out equally to both. You aim for the best idle speed, but no weaker.

This does assume the carbs are within spec as regards wear, etc.

[R0vers]

With Stromergs, the jet shoulders should be aligned as a starting point. The carbs then balance for flow, and any mixture adjustment carried out equally to both. You aim for the best idle speed, but no weaker.

This does assume the carbs are within spec as regards wear, etc.

i think my problem lies with the position of the needle -

(Option A) Is it the shoulder of the thin long brass needle itself that should align with the bottom of the piston?(there is a very thin black washer at the top)

OR
(Option B) the shoulder of the sprung loaded spring housing, which holds the needle in place?

here is a link to a sketch i did to help explain

http://s33.postimg.org/8c2uekaof/Stromb ... ostion.jpg

Also, when tightening the small grub screw in the side of the piston, should this clamp the spring housing in place- or should the spring housing be allowed to slide freely within the female housing?

[R0vers]

I decided to replace both needle sets as i wasn't convinced by them as they has a slightly chamfered shoulder, and all others I have seen reference to have a square shoulder. there were also sitting proud of the piston, which i assume was the reason i had such rich readings.
Anyhow - the adjusting screws deep inside the piston were gummed up and needed some persuasion to get free once more - but got there in the end.

The new adjustment needles now sit flush with the underside of the piston and are both equal on each bank...

It seems to be a real grey area on how to properly fine tune the Stromberg’s, but I hope for now I’ve got it close enough to use and check it out on the emissions machine when I can.


I’m hoping to go for a longish drive tomorrow, so fingers crossed!