Amazon: Carburettor options?

[woodman]

Hello,

I'm running on a single Stromberg CD175, the old one with the easy mixture adjustment. After overhauling it twice in 30,000 miles I still don't feel it's really doing the job: I get quite lively performance but I can't get an even mixture across the throttle range, which means it's either weak and lumpy at idle or too rich when opened up. It also drinks dashpot oil like I drink wine...

After reading various threads on here over the years I'm coming to the conclusion that a more modern single SU from a Montego would be a good option, though when I saw 123GT-Amazon last week he was also thinking that a more recent Stromberg from a Volvo 740 might be a good bet. (Mind you my Auntie who loved her 740 always complained about the fuel consumption...)

Now that the car is running so well otherwise I feel this might be the next thing to tackle, so I'd welcome any advice about more recent single carbs that are easy to tune and give a better mixture progression.

Thanks, Andy.

[Clan]

Originally Posted by woodman

Hello,

I'm running on a single Stromberg CD175, the old one with the easy mixture adjustment. After overhauling it twice in 30,000 miles I still don't feel it's really doing the job: I get quite lively performance but I can't get an even mixture across the throttle range, which means it's either weak and lumpy at idle or too rich when opened up. It also drinks dashpot oil like I drink wine...

After reading various threads on here over the years I'm coming to the conclusion that a more modern single SU from a Montego would be a good option, though when I saw 123GT-Amazon last week he was also thinking that a more recent Stromberg from a Volvo 740 might be a good bet. (Mind you my Auntie who loved her 740 always complained about the fuel consumption...)

Now that the car is running so well otherwise I feel this might be the next thing to tackle, so I'd welcome any advice about more recent single carbs that are easy to tune and give a better mixture progression.

Thanks, Andy.

I would fi the twin SU carbs which were standard on the 122S they are a known quantity regarding jets and set up rather than random carburettors off other cars which need calibrating properly , not an easy job ..

[Derek UK]

You shouldn't have to rebuild the carb twice in 30kmiles unless you're not actually addressing the actual worn parts. Not much to wear anyway. Temperature compensator on this carb? If so that needs to work properly. Correct needle?
This carb will work fine with a better cam than the A you probably have but not much point adding an expensive pair of SU's without changing the cam.
Twins with an A cam will give you worse consumption.
A single HIF would probably work fine IF you can get it set up properly. I think the Maestro ones had a sort of stepper motor and damper to improve emissions which might be best removed. MG Metro maybe?

[woodman]

When I say rebuilt twice, what I mean is that I bought a rebuilt one from that reputable firm down south whose name escapes me now, but then subsequently changed the jet and needle again from Burlen, because the needle was bent - I don't honestly know whether I'd bent it or someone else had, but it had worn the jet out of shape too. The diaphragm is fine. Now it starts and performs fine but it still has this problem of uneven mixture progression. As you suggest Derek, this might suggest the wrong needle, but Burlen assured me there was only one correct needle for my carb, and that was it.

I have a bias towards SUs because in the past I've had a Metro, a Montego and four Triumphs, two of which were twin carbs - so that's eight SUs, and I can't say I ever had a single problem with any of them.

[classicswede]

The CD175 is a great carb and equal to the HIF SU, both are better than the HS range in my opinion.

Burlen are good with getting the right parts so your needle and jet should be correct. The mixture is simple enough to adjust.

If getting fueling right accross the range is the problem there are 3 likely causes

1) wrong oil or no oil in the dashpot. The CD175 uses ATF but if it is leaning on acceleration going to a thicker engine oil would help

2) worn spindle or other area of air leak

3) wrong needle or jet

[swedishandgerman]

When you say uneven mixture progression, what do you mean?

I can't say that I've ever had a problem with a Stromberg CD175 and I would never consider swapping it for anything else - that is unless I was going for a full job including cam etc - but I'm not clear on what problem you're experiencing.

If I was you, I would stop fiddling about with the carb you have and get hold of another identical carb

I had a Montego carb on my previous Amazon Estate. There was sod all difference, but there was this irratating thing where was unable to adjust the linkages and rods to be able to get full open throttle

[woodman]

Maybe that's answer, Adam. I just get another CD175, take my time on the workbench and rebuild it myself, so I know exactly what it's doing.

What I mean is, the mixture tends to be weak at idle and rich when opened up - which I accept could also be caused by a leaking seal, but with a carb that I paid to have rebuilt I suppose I was assuming this wasn't the problem.

It's not a big problem but it's enough to throw the numbers off when you put it on a gas analyser, and I think it's a point of principle for me now - the carb should be capable of working perfectly, so that's what I expect it to do.

[coaster22]

My 1983 240 has the single Stromberg CDSE type carb, had similar issues until an overhaul last year. Have had experience with SU HIF carbs on MGB V8, prefer the simple robust Stromberg, just ordered gasket set and O ring as you mentioned the dash pot oil disappearing, this is the small rubber O ring which will have perished and needs replacing, you can buy the Allen tool to do this .I use ATF in my dash as suggested A number of rebuild guides on the web, good one on a Triumph site as I remember. My own opinion is stick with the Stromberg.

[Alf ista]

I have the Stromberg on my car and it has given zero trouble in all the time I have had the car. Well, except for a failed diaphragm. I know you said yours is alright, but maybe changing it would be worth it in case there is a pin hole?

[guitarman]

I'd concur with the above. The needle is critical. Diaphragms are cheap as chips. Likely to be shot full of holes but I feel Strombergs are good carburettors, which rarely need fettling.
No air leaks?