Carb issues

[Desperate Damson]

Hi Guy's

Question for you!!

I currently have a pair of Strombergs (CD150's) fitted to my GT6 MK3 but they need replacing, it seems Strombergs are pretty rare, can you use SU's on the same manifold? Do i have to do any mods to make it fitt/work. As a few people have suggested this as a option.

What you think?

Paul

[Clive]

Plenty of strombergs around if you look, or they can be rebuilt.
It you want SU's then the dashpots are a tad tall and hit the bonnet, also the bolt holes are the opposite way round so need an adapter plate. It can all be done though. Or fit the short dashpot HS6 carbs from a sprint, again issues with holes, opening up the manifold and making a linkage......
Saloon manifolds no use as they are not stepped down like the GT6 one.

[Dale]

As Clifty says there's a lot more work involved in converting to SUs than in rebuilding your Stroms. All the bits are available and even if the bodies are so shot that they can't be simply inserted (ooer) and re-spindled (unlikely) there are loads of s/h bodies about.
   Unless you're about to do some fairly serious engine mods and want to avail yourself of the greater range of metering needle options with SUs, I wouldn't bother, just rebuild the Stroms.

[Desperate Damson]

Well to cut along story short, i rebuit my current set of carbs (Strombergs) when fitting the main jet which needs to be punched in the centre of the carb, i never found a depth for this jet and there is no depth stop, consulted me Haynes manual, no mention of a depth for them, so fitted them as near as the old ones were fitted. But once running the carbs have no adjustment at all, it picks up ok but no bottom end at all almost stalls. Some people have suggested the jets are too high, but because they are only brass im reluctent to try to punch them in a little more.

Also inside bottom of the oil damper, just about the needle there should be a star washer which holds the needle in place but cant get these anywhere, so im stuffed!! I have tried Rimmers and also Burlen who make the carbs, no luck.

Sorry it a long answer. ??)

Cheers
Paul

[thealligator]

Strombergs dont you move the needle to adjust the mixture not the jet,

The star inside damper is what adjusts the needle I think

[junkuser]

Which model 150, ie, what letters follow the "CD 150"?

[thealligator]

This link may help:

http://www.gowerlee.dircon.co.uk/Stromberg.html

They may stock your bits as well

[rotoflex]

It sounds to me like Paul has the CDSE's.

They have a fixed jet, & the needle is adjusted from above via a mechanism in the center of the hollow dashpot piston shaft.

The jet is punched in.

Paul has actually been more adventurous than I.  I just leave the old jet in place.  I recently had a whim to go ahead & replace it, & when on the phone with a US Stromberg/SU specialist (Joe Curto), was convinced to just leave it unless scorin inside is evident.  If it must be replaced, he recommended sending it to someone who is set up to work on them.  Almost all the time, it's fine when a good needle goes back in.

The problem sounds like it is the undocumented mechanism for needle adjustment in the dashpot.
There is a page online wherein a TR6 owner talks about working on it:

http://www.bowtie6.com/CarbRepair/index.htm

The mechanism consists of a star washer, a small threaded bushing which adjusts the needle, & an O-ring which fits into it.



Usually on older carbs, the only problem here is that they leak dashpot oil into the carb body due to the O-ring's deterioration over time.  But sometimes, the threads are stripped on the threaded bushing, which means the needle can't be adjusted.

That is an excellent page covering the service of that assembly.  I'd suggest contacting some Stromberg places over there to see if someone has new parts, or even very likely some junkers they use for parts for the replacement star washer (& threaded bushing, if neccessary).

The O-ring is often not included with carb rebuild kits, & since the adjustment assembly itself is not covered in any book or instruction insert I recall, it's likely neglected by previous owners & unknown to them how to fix.  A problem with its lack of documentation & replacement part inclusion is that often the pistons are just dunked in carb cleaners during a rebuild (as the instructions don't say what's in there), & the parts cleaner dissolves the little O-ring (as it should, really, petrochemical parts are supposed to be softened & dissolved by parts cleaner).

I can appreciate your frustration now with the Strombergs, but I think with this information you can get back underway & achieve a good result.

Often SU/Stromberg arguments boil down to not very useful Chevy/Ford -type partisanship, but I really believe that for most casual, daily drivers the Strombergs are the better units - short & long-term, they're easy to live with.  

Vacuum leaks on carbs are the most frustrating & difficult problems for most folks to chase, & often on SU's or Strombergs its due to throttle shaft scoring or wear at the throttle shaft bearings.  On SU's, the throttle shaft (if scored or worn) must be replaced (sometimes with a larger diameter unit), & the throttle shaft bearings replaced (involving reaming), which is a more aggrvating procedure than on the Strombergs.  On the Strombergs, the seal at the throttle shaft is via throttle shaft seals, in which the throttle shaft is partially held,  Usually, if the throttle shaft on a Stromberg is scored (found at rebuild with a fingernail), the solution is simply to get another, standard-size throttle shaft (cheapish), polish the insides of the bearings a little, & fit new throttle shaft seals.

Some kits do not include throttle shaft seals (part 21 in the diagram on the page below)
http://www.gowerlee.dircon.co.uk/Stromberg.html

But good kits do, & should.  Even if they have no problem at disassembly for rebuild, parts cleaner will of course attack them & cause them to deteriorate, & removal for cleaning often injures them.  Replace the throttle shaft seals at rebuild, attend to the interior condtion of the throttle shaft & its bearings, & the throttle shaft just plugs on forever.  Even with minor scoring, new seals will prevent a vacuum loss there - you can run well on wear there that would make an SU unmanageable.  

Always confirm with the rebuild kit supplier that the kit contains throttle shaft seals (double check or go somewhere else if it seems to be a counter-jockey who just responds "Oh yeah, it's got everything you need".  If you have CDSE's, you must anyway confirm that the kit includes the diaphragm for the throttle bypass valve (Not shown on the illustration on the page below, it is sandwiched between the two halves of the throttle bypass valve assembly number 17)
http://www.gowerlee.dircon.co.uk/Stromberg.html

Here, this diagram shows it #12:
http://www.spitbits.com/gt6/GT6%20fuel.htm

A lot of words for problems that can be dealt with more directly.
1.  Disassesemble the needle adjusting mechanism in the pistons per the page at
http://www.bowtie6.com/CarbRepair/index.htm

2.  Esamine what you've got, if you'll need new star washer, threaded bushing, &/or O-ring.

3.  Contact a Stromberg specialist over there to glom needed replacement parts off a junker, & a new O-ring.

4.  Put it back together, & do the mechanism in the other carb too.

5.  At future rebuilds, always attend to the needle adjustment mechanism & throttle shaft condition (w/fingernail test), & confirm with the kit supplier that the rebuild kit includes throttle shaft seals & the bypass valve diaphragm (often an extra-cost part).

---

Speaking of the CDSE's throttle bypass valve assembly & vacuum leaks:  the throttle bypass valve (shown at # 17)
http://www.gowerlee.dircon.co.uk/Stromberg.html

Can vex some folks.  It does not affect performance, it only comes into play when you take your foot off the gas & the throttle snaps shut (in fact, the only possible performance-reducing item on the CDSE as opposed to the CDS is the needle selection).

However, since Haynes & other rebuild instructions do not cover the assembly any more than to say "Don't disassemble it", it can over time be the source of a vacuum leak even if the gasket between the bypass valve assembly (# 18 ) & the valve's internal diaphragm (the one mentioned earlier that usually must be bought separately) are replaced.

The throttle bypass valve has at its end a little brass plug over an adjustment screw.  The plug can be extracted (broken up) & the screw seen.  There is a small rubber washer around the top of the screw sealing the unit.  If the bypass valve is not disassembled for rebuild, two things happen over time:
1.  Haynes says don't disassemble it, & someone just chunks it in some parts cleaner.  The diaphragm deteriorates, & does affect performance or evolves a vacuum leak there.
2.  Haynes says don't disassemble it, & someone just chunks it in some parts cleaner.  The little rubber sealing washer deteriorates & a vacuum leak occurs there.

Oddly, even though rebuild kits often don't show the bypass valve disassembled, they often include the little sealing washer.  You will have to remove the brass plug over the end to completely disassemble the bypass valve & replace the little washer.

That is simple enough, & does require very coarse adjustment of the screw when the carbs go back on to get it so that the bypass valve does not function when the throttles are opened in operation.

But I was talking with my friend Pierre who does good works among the heathen & their MGs, & he mentioned that some MGs use the same carb WITHOUT the throttle bypass valve.  The carb body has the face there for it, but the passages aren't drilled.  If you're one of the people who like to fix things so that you don't even have to think about them anymore, & it doesn't fall afoul of emissions regulations there, it seems like you could cut a blanking plate to go under the bottom of the bypass valve assembly with scissors from some thin sheet aluminum (or aluminium, or whatever, cheap stuff, it doesn't have to be platinium),  put 3 hole in it for the bypass valve's carb-mounting bolts, then assemble onto the carb in the order (carb body) <- (bypass valve gasket) <- (blanking plate) <- (bypass valve assembly)

The idle would likely change & need to be re-set, but the potential for leaks in the bypass valve would be eliminated.  Whatever it is that the bypass valve does at throttle close it wouldn't do no more, of course.

[Greeks]

Purr

I haven't read all of that above ... and I'm sure it's good of course ... but

Just speak to Andrew Turner, carburettor guru (strombergs, su), who also uses this site.
He's quite excellent, and a good source of advice as well as parts.
http://www.su-carbs.co.uk/

[Desperate Damson]

I did enquire about a set of Strombergs, but found £175 a bit much even for a rebuilt pair. I might contact him regarding the centre jets.

Paul

[Desperate Damson]

A bit of an update for you. After speaking to Andrew Turner about my issues, he gave me the information i needed. Last night after receiving all the bits, i thought i would have a go at adjusting the jet heights, after a bit of fiddling it seems to have done the trick, the car runs well trought the rev range no spluttering etc, although i will need to take it for a longer run to make sure i haven't no gone too rich.

Thanks to all who have been a great help

Paul ;D

[rotoflex]

Well, that made my day.
I hope it all sorts out perfectly!