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JClug

Replacing Stromberg with SU carbs?

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Hi, 

I would like to hear from anyone that has replaced their Strombergs with SU carbs. Is this worth doing, or even a good idea? Do they work as well with the TR6 engine? Are there other considerations one has to keep in mind? Problems? Thanks in advance.

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Why...just why ???? :(

What is it you are hoping from SUs ?? More power? More needle options? Easier to work on ?

Just curious about your motives.

Jochem

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My friend Frank has SUs HS6 on his TR250, installed by the previous owner.

He told me this should be Strombergs and asks himself the same question the other way round.

So the answer from someone who did both, and can compare objectively, would be interesting.

Ciao, Marco

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Let us have a name, we are a nice friendly forum, and welcome.

jochem has it in one = Why.

Strombergs are a fine carburettor, I've had them on my TR4 for over tewnty years because although it came fitted with the 'wrong' SU's,

Strombergs were correct for my car.

So I did the swop, never regretted it and see no reason to change, They stay in tune, I've never had to change a diaphram, though do carry spares and for me it has been a success.

The ONLY reason you might consider moving to SU's is a greater availability of needles, perhaps useful if you wish to alter /experiment with your car, upgrades, rolling roads etc., but other than that I really can't see the point.

John.

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Welcome to the forum, JClug.

A bit of an introduction (hint) from new joiners is always appreciated.

I did the change from Stromberg to SU in a previous car, around 1990. No internet, no TR register, just me.

It made no noticeable difference, but I liked the looks of the SU’s better.

Enjoy the TR.

Waldi

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4 hours ago, JClug said:

Hi, 

I would like to hear from anyone that has replaced their Strombergs with SU carbs. Is this worth doing, or even a good idea? Do they work as well with the TR6 engine? Are there other considerations one has to keep in mind? Problems? Thanks in advance.

Hi - I agree with many of the sentiments already expressed - Strombergs seem to have developed an unfair reputation - you can replace them with SUs and TR Shop do a kit with linkages for £795, but there are companies around who will restore your existing set up, including the manifold and linkages for a lot less - I've used GW Carbs ( https://www.sucarbs.co.uk/) as they are local to me in Essex and they do a cracking job - have a look at their website to see examples of their work  - no association other than a satisfied customer

Cheers   Rich

 

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When I first had my TR6 I replaced the worn Strombergs with new SUs and they were ok, nothing spectacular but ok. The SUs eventually wore out so I had the Strombergs repaired and now run with Strombergs again and the car somehow seems a bit smoother.

George

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5 hours ago, JClug said:

Hi, 

I would like to hear from anyone that has replaced their Strombergs with SU carbs. Is this worth doing, or even a good idea? Do they work as well with the TR6 engine? Are there other considerations one has to keep in mind? Problems? Thanks in advance.

I think the main reason is if you modify the engine then there are far more options (needles) for tuning it correctly.

Darren

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I’ve a 150CP with HS6s on a 2.5s Manifold with Dolly Sprint KN Filters with richer Needles and the Car flies and  yes it’s a Spitfire.

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I replaced my Strombergs with SU’s earlier this year. Reason was that the Strombergs was worn with idling problems etc, probably too much play in the spindles. Got a pair of second hand SU’s in good condition, think I paid around £90-for the pair, spent some money on gaskets etc, also bought some parts on spindle connections etc. 
 

I’m very happy with the result, a bit easier starting and a better idle, in terms of performance it seems the same, possible the Strombergs performed a little bit better on high revs? Might just be a feeling and not a fact.

On the plus side SU’s looks better, and is easier to work on, on the minus the original air filter does not fit but not a big deal for me.
 

Will keep the Strombergs as they are original to the car and could possible be restored, taking them apart it is obvious that the Strombergs are quality carbs, and like for like better than SU’s in terms of machining tolerances.

 

Magnus

Edited by TRseks

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9 minutes ago, TRseks said:

I replaced my Strombergs with SU’s earlier this year. Reason was that the Strombergs was worn with idling problems etc, probably too much play in the spindles. Got a pair of second hand SU’s in good condition, spent some money on gaskets etc, also bought some parts on spindle connections etc. 
 

I’m happy with the result, a bit easier starting and a better idle, in terms of performance it seems the same, possible the Strombergs performed a little bit better on high revs? Might just be a feeling and not a fact.

On the plus side SU’s looks better, and is easier to work on, on the minus the original air filter does not fit but not a big deal for me.
 

Will keep the Strombergs as they are original to the car and could possible be restored, taking them apart it is obvious that the Strombergs are quality carbs, and like for like better than SU’s in terms of machining tolerances.

 

Magnus

What Inlet Manifold are you using Magnus?

 

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Welcome to the forum.

I've been impressed by the Strombergs on my GT6.

After refurbishing them many years ago and setting them up carefully, they held their tune for years and thousands of miles. Rumours of unreliability or split diaphragms are just that, rumours rather than fact.

The only reason I could see for switching to SUs would be to get a wider range of needle choices when setting up a modified engine. So we come back to the question asked by Jochem: 'Why?'.

Nigel

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I’ve had a couple of split diaphragms over the years, I’ve also had the needle O ring perish & leak but nothing serious has gone wrong with Strombergs I’ve had, then again, nothing at all has ever gone wrong with any of the SU’s I’ve had.

Edited by iani

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Look upon a Stromberg as an over complicated equivalent of an SU.

Similar when working well but with more to go wrong  - diaphragm an o rings to fail but more expensive to rebuild.

Should you actively swap from another? Not really. If you want a swap for performance consider Weber or injection. Strombergs have less scope for alternative needles than SUs when making changes after cam swaps or other tuning.

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Originality wins this contest, as no claimed or actual performance benefits result from a conversion either way. Values decline when there are deviations, with few exceptions.

The only carburetor conversion with any prospect of increasing value would be Weber DCOE, and only if they're properly calibrated ( a black art to most onlookers ) when they deliver the goods in accordance with their reputation ( world's best ). On an emissions spec engine these won't deliver an iota of additional performance however.

For the emissions / U.S. spec TR6 the original Strombergs can't be beat for compatibility and...low emissions. While we're on the topic, an early TR6 Carb with O/D can deliver 34 mpg US on the highway - more than 40 mpg Imperial. This is a little touted attribute.

 

Cheers,

Tom

Edited by Tom Fremont

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Both basically work by inlet vacuum causing the piston to raise letting in more fuel & air as the butterfly is opened, but whereas the SU relies on the upper piston Suction Disc in the top Suction chamber (which can wear) to make a seal the Stromberg has the diaphragm which makes a perfect seal and can easily be replaced. Both good when new but when worn the Stromburg may have the edge.

Chris

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Hi again,

First of all thanks for all the answers and opinions - and I can see that the central question to answer is "Why?" Why change Strombergs to SUs? 

Sorry I forgot to introduce myself. My name is James C., I live just south of Ottawa, Canada, and I began a "small restoration" of a 1972 TR6 approximately 9 years ago. Well, as is the case for many of us I expect, it turned into a full blown body-off, frame-up resto. I got the whole thing into pieces then I lost my rented garage, so the project sat for a few years not being worked on. The 6 survived a move to a new house, and now - 9 years after starting - it sits in a nice big new garage with about 25 parts bins and is waiting to be put back together. The tub and wings etc., are off getting painted, the drive-train is back on the chassis, all new bushings installed, new springs and shocks, muffler, brake parts etc., the usual line of a million things. 

Now to the carbs: In taking the engine apart, I noted that the Strombergs had been running roughly, they were filthy and no doubt in need of a rebuild. In the meantime, I had come in to a pair of rebuilt SU's. Having had a TR3 long ago and an old Volvo - both with SU's - I am more familiar with them, found them very stable and easy to maintain. So, I was thinking of trying out the SU's and if they don't function well, was going to rebuild my original Strombergs. I think I may continue with my plan just to see how well (or not) they perform, and meanwhile rebuild the Strombergs to have them ready to go "on the bench". In the last few weeks I ran a bench (chassis) test of the motor using the SUs; the engine started easily and ran very well, bearing in mind that it hadn't been started in about 5 years. My "English car friend" knows how to tune the SUs, so we balanced them and he seemed quite impressed with how they functioned. So we know they work sitting in the garage in neutral, how they would fare under load remains to be seen.  But...I'm going to order the Stromberg rebuild kit... just in case.

So why change? Just because I have them sitting there ready to go, already rebuilt. Perhaps not reason enough?

James

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Hi James,  sounds a good plan to me. If they end up driving well I would keep them, save your money on the Stromberg rebuild you may need it for something unforeseen.

As they say, if the toast  tastes good who cares who made the bread.

Chris

PS: Keep us posted with your progress, some photos would be great.

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Hi James,

Great to hear a bit more about your TR6 project, looking forward to updates as it progresses. Well done for dealing with the practical difficulties of holding on to your project while moving house, and all the other stuff life inevitably throws at us.

Strombergs or SUs should work fine. If you go with your 'on the bench' SUs, members here will be able to help with needle recommendations.

Please let us know how you're getting on with your car (better still with photos) and ask any questions.

Good luck,

Nigel

 

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12 hours ago, TR NIALL said:

What Inlet Manifold are you using Magnus?

 

Same as for the Strombergs, the engine on my car is 1970, but the head is from 1974 so assume original inlet manifold for a 1974 US car.

 

 

Magnus

Edited by TRseks

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I changed to SU HS6 carbs many years ago with no regrets, but no performance gains either. I like the simplicity of the SU, the ease of accessing the float needle valve (in case it becomes clogged, the ease of adjustment, and the fixed needle. Even with all of the SU needles available, it still requires fiddling with the profile to suit various engine mods.

The choke mechanism of the ZS carb is easier to operate, the throttle shafts have replaceable seals and ride in steel bushings. But the o rings in the damper and the float chamber have a tendency to leak. The temp compensators and throttle bypass valves can be disabled to eliminate problems.

Both carbs have their weak&strong points and are more similar than different. 

Berry

 

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Wow, what a welcoming and helpful community of Triumphers. Thank you all so much for your kind words. Pictures, you say? I tried uploading one but my pics are too large - I will reduce their size and send later.

J

 

 

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Just found this YouTube video on conversion from Strombergs to SU’s, I found it interesting:

 

 

 

Magnus

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One of the issues that I had when changing to SUs was the port for the distributor vacuum unit is set for vacuum advance as opposed to the Stromberg which is designed to operate the TR6's vacuum retard.

When I had the distributor rebuilt I had it converted to vacuum advance which was fine until I changed back to the Strombergs so now I have the port blanked and the vacuum unit is not used.

I also noticed on the video posted by Magnus that the chap connected the float chamber vents to the carbon canister, I know that the Strombergs have this line but they also have an internal vent that is in use for normal running and the vent to the carbon canister only comes into play when you turn off and the anti run on valve directs vacuum to the float chambers

George

Edited by harlequin

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