SU vs DCOE for Tractability

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addo
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SU vs DCOE for Tractability

Post by addo »

I have another project that is under some pressure to restart.

It involves a car with (presently) twin DCOE carbs, one of which was not running happily several years ago; the other may now have followed suit. They're on a '60s Standard Triumph motor with headers and a lumpy cam. Ignition is presently standard, and I suspect worn bores.

My thinking was to replace the carbs with two SU 6s or even 4s on a standard manifold, at least for the time being as this should (?) simplify tuning and idle stability. Or am I barking up the wrong tree? Weber rebuild kits are quite cheap now, but I have nil experience with the carbs and imagine that you'd need a bung in each header pipe to tune them with a wideband O2 kit. I don't even know where to start with a Weber, if you tune the idle circuit first or get the main jetting right, then work around that.

In a perfect world it would get an EFI conversion but that's not feasible at the moment.

So - looking for words of cynicism and general discouragement... How to tread through this with the least amount of muck sticking to my shoes (ie; lingering issues to sort)?

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Re: SU vs DCOE for Tractability

Post by lexi »

I think my triumph 2.5 pi made 150 bhp with Lucas injection. The earlier 2000 and 2,5 carbies were all Stromberg.

You are going back to Hot Car magazine stuff with this Addo. I forget all of it and I had Ford crossflows with many webers and piper camshafts Janspeed branch manifolds etc etc :lol: About 6 yrs ago I threw out 3 hundred of those old mags, Cars&Car Conversions and Hot Car. The info was priceless for this stuff, as every combination was in those mags in detailed build stories, for all of those old engines.

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CitroJim
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Re: SU vs DCOE for Tractability

Post by CitroJim »

Adam, the SU always enjoyed an excellent reputation in the day. It was by far the best part of any BMC car!!! I jest but in the words of all the old tuners they were unbeatable really so I'd be happy to suggest you're on the right track there..

Getting the right needles and dashpot springs might be a bit interesting but there’s so much information out there it should not be hard to find a good starting point..

A lot easier than buggering about with trying to tune a DCOE without doubt and a bloody sight cheaper too.

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Post by addo »

I'm a cynic when it comes to "Ran good when parked" as the Seppos like to say. Quite possibly the Webers are a hacked-up, mismatched set thrown onto a worn out motor. I could be wrong, but it's madness to hope for better than reality suggests.

Sounds like SU HS4s may be the starting point. I think the manifolds as delivered, are made for that throat size, not HS6s. The car needs a lot of fiddling to get back in roadworthy shape, although the body is quite sound. Once it's being driven more, I think the owner will be sufficiently motivated to sort some stuff properly.

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CitroJim
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Re:

Post by CitroJim »

addo wrote:I'm a cynic when it comes to "Ran good when parked" as the Seppos like to say. Quite possibly the Webers are a hacked-up, mismatched set thrown onto a worn out motor. I could be wrong, but it's madness to hope for better than reality suggests.
The words of a wise man...

And the DCOE can wear badly as well, far worse than an SU. Have you seen how many bits are in a DCOE repair kit as against in an SU repair kit..

Fact is, if it ran good when parked up it would never have stayed parked up for long...

In the same tone as you see in dodgy ebay listings: 'Needs slight attention to the....' which in reality means it's a total disaster and is fit only for the bin.

My favourite: 'Slight electrical issue. May be a fuse' If it's just a fuse than why not do it before it goes on sale then. No, you know the problem would stump all the engineers at Jodrell Bank it's so complex and difficult...

Have you seen the books by David Vizard, particularly his BMC A Series tuning bible? He rates the SU above all else for normal use and goes into exquisite detail about them.

What engine is it exactly Adam? We had four pot and six pot Triumph engines here from little baby ones as in the Herald right up to the hairy arsed 2.5 six.

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Re: SU vs DCOE for Tractability

Post by lexi »

Made me laugh enough Jim to think of "Car is not Mot'd but I can put a ticket on it"........Well I suppose it would help :lol:

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Re: SU vs DCOE for Tractability

Post by xantia_v6 »

You haven't told us which engine it is, but if the manifold takes hs4s, I guess it is a 1300 or 1500. I think the 2.5s were fitted with hs6s.

http//www.mgexp.com/article/all/Tuning_SU_Car ... sport.pdf‎ is well worth a read.

My dad was (among other careers) an expert tuner of Solex/Weber carbs, unfortunately he gave that up and sold all his carb spares before I could walk. He said his most bizarre tuning job was fitting and tuning a pair of Solex carbs to a vintage Rolls Royce to improve the fuel economy.

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Post by addo »

It's an FH series block (1296cc, 9.0:1 nominally), out of a Spitfire Mk 4.

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Re: SU vs DCOE for Tractability

Post by spider »

I can recall many years ago my dad made a manifold enabling him to fit an SU onto his 2CV :) Not sure if that was the R or V plate one, both were quite old when he had them though, he had the V plate in about 85/86 going from memoryy. I may still have the homemade manifold somewhere.