Triumph twin Strombergs...

[philcoyle]

Re: Triumph twin Strombergs...

I still do not see how you can have manifold depression/suck/vacuum if the porting in the carbs is not linked directly to the manifold, as you say Peter the Y piece should be connected to the manifold.
At the moment the servo is connected to the manifold, but the carbs are connected to the engine breather which is pressurising the carbs and not creating a Constant Depression.
Just humour me for the moment and disconnect the servo hose, not forever, and connect the carburettor pipe you have going to the rocker cover onto the manifold.
This should now give you C.D. and then we have to work out where the engine breather is going to fit and of course the servo pipe, but one step at a time.
What you have at the moment is Constant Pressure from the crankcase and not Constant Depression from the manifold. I said earlier the answer was staring us in the face, Constant Depression Carburettor, they have to have vacuum/suction/depression, as soon as the engine turns over. I don't know how many more ways I can express this.

Pipe off rocker cover.
Servo pipe removed from manifold, temporarily.
Connect pipe with the T piece to the manifold.
Cross fingers and everything else turn the key.
Even I'm getting depression.

[greyV8pete]

Re: Triumph twin Strombergs...

I Googled “triumph gt6 inlet manifold” and clicked on images.

It seems to me that your Y-branch should go to the rocker cover via an emissions PCV valve thingy that presumably will shut off when the engine starts to run and the inlet vacuum pulls it closed. Then the air will have to go in through the carbs. The other connection on the top of the cast inlet manifold should be blanked off?

http://www.rimmerbros.co.uk/Item--i-GRID008001

http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1396120436/

The link below shows twin SU carbs with a similar idea but using the inlet manifold connection as there aren’t the pipes on those carbs like your Strombergs.

http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl/Blah.pl?v-print/m-1259491759/

I would try temporarily blocking off all the pipes and see if the engine will run. If it does then decide which pipes you want to connect the valve to. My money would be on using the Stromberg connections via a Y-piece via the valve to the rocker cover and then blanking off the manifold boss.

Peter.

P.S. I have crossed posts with Phil. Seems like we are on the same wavelength and getting somewhere! PL

[greyV8pete]

Re: Triumph twin Strombergs...

Ah yes! Just looked at your very first post and the pipe across the engine goes to the servo. So, connect that to the single boss on the cast manifold balance pipe. Connect the rocker cover pipe to the PCV valve. Connect the PCV valve to the Y-branch with the legs of the Y going to each carb pipe. Be sure to connect the PCV valve the right way around and I bet it will work! Peter.

[philcoyle]

Re: Triumph twin Strombergs...

Well done Peter it appears you have cracked it, the first post shows a 1/2inch bsp T piece connected to the manifold and servo, and the PCV and this part doesn't seem to be on the engine now.
I've learnt a lot today about Triumphs, think I will stick with my EFi for now.

[David]

Re: Triumph twin Strombergs...

Yes the manifold take off is for the servo, used to come off a T which also had the PCV. It is connected to that non return valve on the manifold.

The rocker box breather goes to a PCV on older setups but these newer carbs have an inlet for the breather which is the Y piping. The Y piping and new inlets on the carbs replace the PCV setup.

I tries Pete's suggestion of blocking the pipes off yesterday, no change.

I think what's confusing you is seeing photo's of earlier (PCV) setups and later carb type breather inlets. Pics below of setups like mine.

GrahamBingham-HF-X10.jpg

513631-1000-0.jpg

Of course I still reserve the right to be totally wrong about this.

David.

[David]

Re: Triumph twin Strombergs...

So after talking to the supplier, it could be that the chokes internal 'mechanism' is 'stuck', suggestions;

1) Pour a small amount of fuel into the manifold which should start the engine and warm up the carbs freeing the choke
2) Pour hot water, or use a hot air blower to warm the carbs and choke for same result
3) Block or reduce the rocker box to carb breather inlet pipes to reduce airflow and thereby richen the mixture

Seems you guys are partly on the right track it seems that later GT6's had reducers on the breather inlet on the carbs to counter some starting issues.

Will report back later.

David.

[greyV8pete]

Re: Triumph twin Strombergs...

Mmmm. One choke stuck maybe feasible but both stuck seems unlikely unless both carbs were poorly stored for some long time?

I presume that the needle jets are adjusted correctly and not just screwed up fully closed?

I would definitely want to block the Y-piece for now. Meantime how old is the fuel? This modern stuff does seem to go off very quickly. I have had problems with my classic not starting if it isn't used much during the winter. I use the top spec fuels (preferably Shell) as they seem to be less prone to this.

Your problem has got me really intrigued. Can't wait for the next progress report! Peter.

[philcoyle]

Re: Triumph twin Strombergs...

You and me both Peter, I hate to be foxed by a manmade machine, so what happens if you clamp the carb to rocker cover pipe very lightly to create a temporary restriction.

Earlier David said the engine fired up on easy start, confirming nothing wrong with electrics or timing but no fuel leaving the carbs. Exit one thought.

Is fuel pump delivering? I see you have an electric pump .

Lifting the dashpots manually doesn't encourage fuel to enter the engine, Why. easy start works okay and not related to the cars fuel system. Third thought.

Did you say earlier that you fitted the one-way valve/fitting into the manifold, isn't it supposed to be on the servo pipe and is it working the right way around, in other words can the depression in the manifold draw air through it when the engine turns over. Need a lie down.

[dogoncrazy]

Re: Triumph twin Strombergs...

Don't these carbs have Diaphragms?
Are they in place/intact?
No diaphragm or split would result in no depression I believe.
Correct me if I'm wrong

[philcoyle]

Re: Triumph twin Strombergs...

David, do you have an assistant who can turn the engine over on the key, whilst you hold your hands over the carbs, covering as much of the intake as is humanly possible. This will act as a choke and the engine has to draw fuel into it, or it will reveal any other pathway that open and is causing the engine not to draw in fuel.

Failing that I am coming to your place with a gallon of petrol and a box of matches, this is getting near to desperation now. think I'm supposed to do smiley face or something.

[David]

Re: Triumph twin Strombergs...

Mmmm. One choke stuck maybe feasible but both stuck seems unlikely unless both carbs were poorly stored for some long time?

I presume that the needle jets are adjusted correctly and not just screwed up fully closed?

I would definitely want to block the Y-piece for now. Meantime how old is the fuel? This modern stuff does seem to go off very quickly. I have had problems with my classic not starting if it isn't used much during the winter. I use the top spec fuels (preferably Shell) as they seem to be less prone to this.

Your problem has got me really intrigued. Can't wait for the next progress report! Peter.

No, a couple of weeks stored apparently.

Yes jets are set correctly

Tried the Y piece block, no change.

Fuel is just 8 weeks or so old and quarter of tank.

[David]

Re: Triumph twin Strombergs...

Don't these carbs have Diaphragms?
Are they in place/intact?
No diaphragm or split would result in no depression I believe.
Correct me if I'm wrong

Yes, they are new.

[David]

Re: Triumph twin Strombergs...

David, do you have an assistant who can turn the engine over on the key, whilst you hold your hands over the carbs, covering as much of the intake as is humanly possible. This will act as a choke and the engine has to draw fuel into it, or it will reveal any other pathway that open and is causing the engine not to draw in fuel.

Failing that I am coming to your place with a gallon of petrol and a box of matches, this is getting near to desperation now. think I'm supposed to do smiley face or something.

Did this early on to see if I could hear air being drawn in anywhere else.

[David]

Re: Triumph twin Strombergs...

So after talking to the supplier, it could be that the chokes internal 'mechanism' is 'stuck', suggestions;

1) Pour a small amount of fuel into the manifold which should start the engine and warm up the carbs freeing the choke
2) Pour hot water, or use a hot air blower to warm the carbs and choke for same result
3) Block or reduce the rocker box to carb breather inlet pipes to reduce airflow and thereby richen the mixture

Seems you guys are partly on the right track it seems that later GT6's had reducers on the breather inlet on the carbs to counter some starting issues.

Will report back later.

David.

So reporting back. First I would say whilst I appreciate the help please check the thread before suggesting things, we may have already covered it

re: above points.

1) No change, runs stops
2) Done with heat gun, no change
3) Done no change

Whilst I was there I also swapped the complete choke mechanism from the old carb hoping that would fix it, no change.

So we now know the new choke is probably working.

Another call to the supplier brings the suggestion, "take it off and check that this other float chamber valve is not stuck". If that doesn't work been asked to return it so at that point I will 'fix' the old carb and put both old ones back on with the PCV setup and then ask for a refund!

Fairly soon I will be wondering why I spend £300+ and didn't just refurb the old carbs myself....

David.

[philcoyle]

Re: Triumph twin Strombergs...

Ten out of ten for tenacity, £300 and a whole month without a result. That's about 20 bottles of Bacardi and one hell of a headache.
Will we know the outcome of why there is a problem with the new carbs?