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GT6 Mk 3 3432 Carbs with one choke + fuel pump


RichardS
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After 40 years of being Spitfire and GT6 free, I've just re-invested in a 1973 Mk3 GT6. It runs and drives well but two things are immediately apparent to me.

The first is that the engine smells of petrol and the second is that, although she starts immediately, the idle seems rather rough until she warms up. After some investigation this weekend, the petrol small clearly comes from the fuel pump which is weeping fuel. I assume that the fuel pump is the standard GT6 item, if there is such a thing, although it appears to be fairly new and does not have any markings on it. Please can anyone confirm exactly what model this is so I can determine which gasket kit I need?

Secondly, it appears that the choke control only operates on the front 150 CDSE 3432 carb as can be seen in the photo, which presumably explains why the cold-running is rather rough until the back three cylinders get up to temperature. From reading other posts it appears that this single-choke arrangement is correct but I wonder whether there is an established practice of changing to twin choke operation?

Many thanks for any help

Richard

 

 

 

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Hi I have the same carbs on my Vitesse mk2 . The front choke feeds the rear carb via the second pipe on your picture . To start I would suggest removing the linking rubber pipe and see if the petrol flows when you operate the choke 

Paul 

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34 minutes ago, Paul H said:

Hi I have the same carbs on my Vitesse mk2 . The front choke feeds the rear carb via the second pipe on your picture . To start I would suggest removing the linking rubber pipe and see if the petrol flows when you operate the choke 

Paul 

Thanks Paul ..... I was thinking that there had to be a mechanical connection between the carbs in order for a choke flap on the inner carb to be closed. Maybe Strombergs don't work like that but enrich the mixture increasing fuel flow rather than by reducing air flow? I haven't stripped one down but I'll do some reading to fill in the gaps. 

Richard

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I have a clear tube linking the choke, so I can check the flow . There’s a good US site which you will find helpful , Buckeye references 175’s , yours are 150’s the operation is the same . You will find your carbs have emission controls which need turning off , this can be done later https://www.buckeyetriumphs.org/carburetors

Paul 

 

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10 hours ago, RichardS said:

 I was thinking that there had to be a mechanical connection between the carbs in order for a choke flap on the inner carb to be closed. Maybe Strombergs don't work like that but enrich the mixture increasing fuel flow rather than by reducing air flow?

Early Strombergs had what Pete calls the "Thames barrier" choke, which raised the piston from the throttle side thus, effectively, increasing vacuum at the jet. Later ones simply supply extra fuel. SUs also just give extra fuel but do it by lowering the jet to a narrower part of the needle. Choke flaps in the air way are a fixed-choke carb thing - Solex or Weber or the like.

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22 minutes ago, NonMember said:

Early Strombergs had what Pete calls the "Thames barrier" choke, which raised the piston from the throttle side thus, effectively, increasing vacuum at the jet. Later ones simply supply extra fuel. SUs also just give extra fuel but do it by lowering the jet to a narrower part of the needle. Choke flaps in the air way are a fixed-choke carb thing - Solex or Weber or the like.

Many thanks. I've only had the car for a couple of days and it's already up on the lift with lots of bits removed, which was not that easy as the narrow chassis rails and bolt-on body make it rather like Series Land Rovers which are also tricky to lift, but Strombergs are clearly something I will be learning about. I've already ordered the "adjusting tool" but I'm sure I'll need to make further appearances on here. 😊

First encounter yesterday with the drain-plug-free diff was also interesting. I managed to pump out all the old oil with the pump eventually but that will definitely be drilled and tapped in due course. Also found that the fuel pump looks exactly like the Rimmer replacement so that will be rebuilt with a new gasket.

Both track rod ball joints were removed yesterday and replacements ordered and the threads re-cut. It looks as if someone had been gripping the thread with pliers to lock the rod in place. 🙁

The sump also appears to have been used to jack up the car so it is now leaking badly, as have the chassis outriggers just behind the front wheels, although not on the strong point where the crush tube/box lies but on the plate sections either side. ☹️

Are GT6 owners always this cavalier? 😕

Richard

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you ask about having two carb chokes   its possible but you need another   front carb and have the throttle spindles changed to make a connection,  in fact we did this by chance when converting the Vit6 from solex to strombergs   its really not worth the hassle and no improvement

i see the breather has been plugged at the carb  so what is your breather system , does it have a smiths valve .its open or what ??

as you have temperature compensators on the side these will be CDSE or similar the mixture is adjusted from down the dash pot with a special or long allen key,

couple of points without going into detail

temp comps best screwed to be shut , turn small nut under the plastic cover , they stay open when old and you cant adjust the mixture 

if you remove the air piston adjust the needle so the small delrin washer on the needle is flush with the base of the piston this is the base mixture setting it should be fine .

if the piston diaphragm is all wrinkled  a wash in petrol will return it to size  there is a  small lug on the diaphragm rim to position things 

use engine oil in the dashpot

+1 for all the clues on buckeye triumphs  good pictures and clear explainations for many parts of triumph

pete

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23 hours ago, Pete Lewis said:

you ask about having two carb chokes   its possible but you need another   front carb and have the throttle spindles changed to make a connection,  in fact we did this by chance when converting the Vit6 from solex to strombergs   its really not worth the hassle and no improvement

i see the breather has been plugged at the carb  so what is your breather system , does it have a smiths valve .its open or what ??

as you have temperature compensators on the side these will be CDSE or similar the mixture is adjusted from down the dash pot with a special or long allen key,

couple of points without going into detail

temp comps best screwed to be shut , turn small nut under the plastic cover , they stay open when old and you cant adjust the mixture 

if you remove the air piston adjust the needle so the small delrin washer on the needle is flush with the base of the piston this is the base mixture setting it should be fine .

if the piston diaphragm is all wrinkled  a wash in petrol will return it to size  there is a  small lug on the diaphragm rim to position things 

use engine oil in the dashpot

+1 for all the clues on buckeye triumphs  good pictures and clear explainations for many parts of triumph

pete

Thanks Pete.

I assume that the blue bungs on each carb are plugging the breather inlets?

My engine has a rubber tube connected to a spigot on the side of the rocker box cover and that just runs down close to the bulkhead and vents to air low down. The open end is not particularly oily or dirty so I guess that there is little blow-by? I can't see any sign of a PCV valve or similar. Is there supposed to be something like that on late Mk 3's?

Richard

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30 minutes ago, Pete Lewis said:

Thanks Pete .... but my engine appears to be newer than KE10000, in the 20000's in fact.

The spigot in the top of my intake manifold is plumbed directly into the brake servo. I'm not sure where else it could go?

I could presumably remove the blue bungs and pipe the carbs with a Y-piece into the rocker box if that is now it is meant to be, but the carbs will presumably have been set up with the current plumbing? It doesn't appear to be running rich but I haven't done much running yet.

Richard

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needs a gt6 guru , the workshop manual for uk only shows a sealed  + smiths valve breather

as you have carbs ( never mind the brass tag as thats easy switched)  that are CDSE  with a breather port 

i wonder if they came  from a 2000 saloon  or they are from a USA spec car you dont have a valve and ports on the carb together 

its one or the other 

sorry guessing  a bit 

 

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2 hours ago, NonMember said:

The Smiths valve was applicable to earlier GT6s. The ones with CDS or CDSE carbs (including most Mk3, certainly from KE10000 on) had the breather ports and rubber Y-piece.

Edit: Relevant Canley page

That's very interesting Rob.

I could certainly plumb my engine like that as it would not interfere with the brake booster.

I wonder whether mine has been modified and the carb breathers blanked off because my engine has been fitted with a hotter cam and had the ports polished etc and blanking off the breather ports has been done to provide a richer mixture which would presumably be required to deliver the extra power?

Does that sound plausible?

Richard

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certainly there are only limited needle specs available for strombergs 

but you can play with damper weights and springs to richen 

so what other things are non standard ,  air filters and goodness knows what 

it all helps in unraveling questions on here ,  even Rob doesnt have a crystal ball  Ha !

Pete

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6 hours ago, Pete Lewis said:

certainly there are only limited needle specs available for strombergs 

but you can play with damper weights and springs to richen 

so what other things are non standard ,  air filters and goodness knows what 

it all helps in unraveling questions on here ,  even Rob doesnt have a crystal ball  Ha !

Pete

Thanks Pete

I'm not sure what has been done over the years as there is a huge file of documents which I have only quickly scanned through. One interesting thing is a detailed valuation certificate from the TSSC dated January 1994. The valuation then was £2500 but, unfortunately, I paid a little more than that. ☹️

I whipped out the 1 and 6 plugs this afternoon and it's definitely running a bit rich, assuming that BPR6ES are the right plugs. However, I would expect it to be rich as it was on choke when I drove it onto the lift from cold a few days ago but at least the two were identical. I'll do a proper plug chop once I'm back on the road.

The new fuel pump arrived today so I fitted it. It's completely different to the one that was fitted. 50% larger so needed some fuel pipe re-routing. I suspect that the original one was some kind of cheap rubbish where you couldn't even get a socket on the nuts because of the poor design. The new one from Rimmers, although cheap, is much more substantial and does have the inlet port integral with the cap which was the source of the fuel leak on the original.

I also stripped down the starter motor today and have now ordered a new bendix as, although the flywheel looks new (I think that is in the paperwork) the teeth on the bendix were very worn such that there was no longer any ramp left on the leading edge. That's another postage charge! 🙁

So  much to do .... so little time. 😉

Richard

 

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i have a hate of any Plugs with an R in my view following cars playing up with BPR5 or 6ES is fit BP6/5 ES and the faults disappear 

it sems to me the weak 22kv HT of our cars is corked up by the supression resistance  fine on more modern with 32kv or more 

i would bin them they are not whats specified anywhere for our triumphs 

bosch have a good review these days NGK do not glazr the centre electrode and choke /rich running contaminates it and they break down 

there  are some good notes in the forum about this 

certainly a run on choke takes a good few hot miles to clean it off

have fun with the bendix 

Pete

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33 minutes ago, Pete Lewis said:

i have a hate of any Plugs with an R in my view following cars playing up with BPR5 or 6ES is fit BP6/5 ES and the faults disappear 

it sems to me the weak 22kv HT of our cars is corked up by the supression resistance  fine on more modern with 32kv or more 

i would bin them they are not whats specified anywhere for our triumphs 

bosch have a good review these days NGK do not glazr the centre electrode and choke /rich running contaminates it and they break down 

there  are some good notes in the forum about this 

certainly a run on choke takes a good few hot miles to clean it off

have fun with the bendix 

Pete

I dismantled the old bendix before I ordered the new one. With the press it's a two minute job, thankfully. There are so many different types that fit the Lucas M35J. 9 teeth, 10 teeth, clockwise, anticlockwise. I just hope I've ordered the right one, 9 teeth, clockwise, but we'll know in a couple of days.

What is the Bosch recommended plug? This is another area where I haven't even started my research yet so I'll definitely start with this forum 

Richard

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