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GT6 Mk3 carb problems.


Qu1ckn1ck
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I have recently bought a GT6 Mk3 (1971).  It appears to be fitted with the age appropriate CDSE carbs and the 311749 early Mk3 inlet manifold but the engine has been replaced  with a later engine, KE21904HE, and the crankcase breather valve is no longer fitted.

 

With ignition timing, tappets and plug gaps all set correctly, the engine runs with the front three cylinders  far too rich, while the back three cylinders are running at the correct mixture.  Can the mixture be made more lean on the front carburetter or is there something possibly wrong with the temperature compensator or throttle by-pass, please  ?  The Insulator and gaskets between carb and manifold have an internal slot , presumably part of the throttle by pass, which the gasket does not appear to fully seal from atmosphere, is this correct ? 

 

I have no experience of Strombergs, would fitting an earlier CD set without emissions control be possible and make life easier, or even an SU conversion ?

 

If I have to have the carbs reconditioned, is there a recommended firm to contact ?

 

All suggestions gratefully received. 

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The mixture is set up separately on each carb. Are yours top or bottom adjusting? Bottom adjusters are easier, top adjusters need a special tool. There could be something wrong with the temperature compensators but I would expect both to be equally shot. Don't mess with the compensator internals, the leak will be the O rings in the carb body. I'd try mixture adjustment first. I knew little about Strombergs  but got a refurb kit from Rimmers, it was easy enough. You have to be careful with the carb to manifold gaskets, there's 3 ways to get it wrong, upside down, back to front and upside down AND back to front. I wouldn't go for SUs but that's personal preference

 

Here is a link to Buckeye Triumphs, it will tell you all you need to know about Strombergs. They are a larger model on the American TR6 but essentially the same. This is part 1, there are 2 further parts, links at the end of part 1.

 

http://buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm

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thin its time you took a tootle over to sunny Luton

 

and i can show you all the things you need to know

 

temp compensators are best fitted with new O rings (2) and adjust to be firmly shut ,  thtas not correct but if you want to adjust mixture at normal temperatures they must be shut , any air bleed will upset any mixture adjustments at idle  just screw the small nut under the plastic cover till the plunger is firmly seated , refit and forget it .its an emmission device to lean off when hot. if its open when it should be closed you will never get its idle mixture correct .

 

 you need to pop over for a cuppa and some clues  some time soon 

 

Pete

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thin its time you took a tootle over to sunny Luton

 

and i can show you all the things you need to know

 

temp compensators are best fitted with new O rings (2) and adjust to be firmly shut ,  thtas not correct but if you want to adjust mixture at normal temperatures they must be shut , any air bleed will upset any mixture adjustments at idle  just screw the small nut under the plastic cover till the plunger is firmly seated , refit and forget it .its an emmission device to lean off when hot. if its open when it should be closed you will never get its idle mixture correct .

 

 you need to pop over for a cuppa and some clues  some time soon 

 

Pete

Thanks Pete.  The GT6 is with my friendly professional mechanic, Tony, who owned and rebuilt an early Vitesse over many years.  Unfortunately he has no experience of the later emission control carbs so I am trying to find answers and source parts for him to fit.  My previous hands-on experience with classics has largely been with MG's from 1932 to 1980, I am now getting too old to do my own spannering so rely on Tony.

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The cdse are adjustable by fitting a tool down the dash pot

two types , a allen key or offset reversed screwdriver these turn a captive nut when rotated it raises or lowers the needle , the jet in the body is fixed on these.

 

the adjustable needle does have a 0 ring seal to stop oil seapage from the dash pot

adjuster is held in with a external star sprag washer

 

if you get something (that fits ) to turn the adjuster set the small plastic washer level with the base of the piston

 

Pete

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This is the adjuster tool, you risk tearing the rubber diaphragm if you just use an allen key. The body of the tool holds the piston in place while you turn the key. The O ring is in the refurbishment kit but not the sprag wash, which is unfortunate, one of mine jumped the length of the garage. Buckeye have a detailed description of how to set the mixture.

 

http://www.rimmerbros.co.uk/Item--i-RX1222

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good point Doug,,  i was making a assumption for twiddling  base settings with the damper piston 'out'  

 

On my tool i added a pair of threaded in tommy bars ,  if the nut adjuster is blasted stiff you cant grip that silly knurled knob

and yes rip the diaphragm , ( who said use Moles ) 

 

the offset driver reverse slot probably appeared in the later 70s to stop twiddling, there were some crass ideas developed to appear to make things 'tamper proof'    with numbered lead seals , tubes and untwiddly odds and sods  but in the end most got chucked over the hedge , dont think it ever became part of the MOT to check tamper proofing .

 

then the emmision dept  closed  apart from diesel smoke and we moved onto tachograph sealing in the factory

I had GBF 01A   the first factory to be granted certification and we went on to prove the need for armoured sender cables to stop 

rogue cross wiring   electronic tachographs   ( before the days of digital)  had some fun with police pulled vehicles 

and driving while showing asleep or resting and alleged poor fuel consumption..  must write a book 

 

Pete

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