Triumph twin Strombergs...

[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.

[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

[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...

Shouldn't the y piece go into the balance pipe? At the moment it seems it will just suck air from the rocker cover? But then it would just duplicate the cast manifold balance pipe. What does the other hose connect to?

[David]

Re: Triumph twin Strombergs...

Any chance of a photo of where the steel balance pipe from carb to carb joins the manifold, I now have a mental picture of the carbs in situ, like peter I don't have a Triumph engine car so everything is a learning curve.

Try this....

[philcoyle]

Re: Triumph twin Strombergs...

Any chance of a photo of where the steel balance pipe from carb to carb joins the manifold, I now have a mental picture of the carbs in situ, like peter I don't have a Triumph engine car so everything is a learning curve.

[greyV8pete]

Re: Triumph twin Strombergs...

That hole is not and has never been blocked. The steel plate in front of it has matching holes, as do the air filters when fitted.

I just updated my last post (weird, typed that whilst end of Edinburgh Tatoo!) to link to. A photo of a manifold identical to mine.

Mind you we are all converging on the probable issue, lack of air fuel mix between carbs and cylinders!

Keep chipping away! I am sure a simple answer is there if only we could see it! It will be interesting to hear what a phone call to the supplier reveals. Peter.

[David]

Re: Triumph twin Strombergs...

That rectangular cut out is the bit that was worrying me Phil, hence the second para in my post #43. If the air can’t get in there then the diaphragm / piston / needle assembly can’t rise. I reckon those Ebay gaskets will solve the problem. Peter.

That hole is not and has never been blocked. The steel plate in front of it has matching holes, as do the air filters when fitted.

I just updated my last post (weird, typed that whilst end of Edinburgh Tatoo!) to link to. A photo of a manifold identical to mine.

Mind you we are all converging on the probable issue, lack of air fuel mix between carbs and cylinders!

[greyV8pete]

Re: Triumph twin Strombergs...

If air was going from filter side to manifold, it would completely bypass the carb, type this on ebay, triumph vitesse gt6 inlet manifold for stromberg CD carburettors,, check out these gaskets on ebay especially the ones with the cutouts.

That rectangular cut out is the bit that was worrying me Phil, hence the second para in my post #43. If the air can’t get in there then the diaphragm / piston / needle assembly can’t rise. I reckon those Ebay gaskets will solve the problem. Peter.

[David]

Re: Triumph twin Strombergs...

Yes the ones with the cut outs are for the carb to filter join, not the manifold to carb.

My manifold is the same as the first one shown in this thread, no holes bar the big one!

http://www.triumphexp.com/phorum/read.php?8,911772

[philcoyle]

Re: Triumph twin Strombergs...

If air was going from filter side to manifold, it would completely bypass the carb, type this on ebay, triumph vitesse gt6 inlet manifold for stromberg CD carburettors,, check out these gaskets on ebay especially the ones with the cutouts.

[David]

Re: Triumph twin Strombergs...

Looking at the last photo the one with red gasket goo on it there is a piece of gasket missing by the oval aperture, and probably why it was running originally, could this have supplied a way for the C.D. to work by allowing the constant depression in the manifold to find a route into the old carbs. It might be worth cutting a gasket or two like that photo and see what happens, have you tried jacking open the dashpot pistons very slightly whilst someone fires it up ( stick your fingers in and lift them a little)
On the Stromberg sectional drawings it clearly shows the passage way from the manifold side of the carb to the dashpot. The reason why they are called Constant Depression carburettors.

Interesting reading on the CD carbs.
P.S. they do not work like S.U. carbs, almost but not quite.

This metal plate is on the filter side of the carbs, not the manifold side so the 'missing piece of gasket' makes no difference really as it'll run with or without the filters attached.

I have tried lifting the dashpot pistons, no change.

I understood the pressure differential was caused by the throughput of air from filter side to manifold side, but I could be wrong. Hoping a call to the supplier sheds some light tomorrow.

[philcoyle]

Re: Triumph twin Strombergs...

I take your point the supplier saying the new carbs would replace the old carbs, BUT, if the old carbs were not correct to start with ?
Also the answer is already there, they are called Constant Depression carbs, if there is no passageway to the inlet manifold they cannot act as C.D. carbs, other than that red gooey gasket cut away.

I would take the bull by the horns and mark out that oval aperture on the inlet manifold using a new gasket, then I would drill a 5mm hole in the middle of the marked out oval at an angle into the inlet manifold, not forgetting to stuff it full of greasy rag first, or you could do it properly and remove the manifold. This way you would have carb and manifold depression linked. If it doesn't work you only end up with 2 holes that wont affect anything, but if it does work?

Just had a cup of coffee and a thought, if all this is too extreme for you, the easy way is to cut several gaskets as per gooey red one, and put two or three between manifold and the steel plate making sure the bottom part by the oval is missing as per your last photo creating a passageway from manifold to carb, in effect creating a spacer. If it works then you will have to get the old drill and files out.

[philcoyle]

Re: Triumph twin Strombergs...

Looking at the last photo the one with red gasket goo on it there is a piece of gasket missing by the oval aperture, and probably why it was running originally, could this have supplied a way for the C.D. to work by allowing the constant depression in the manifold to find a route into the old carbs. It might be worth cutting a gasket or two like that photo and see what happens, have you tried jacking open the dashpot pistons very slightly whilst someone fires it up ( stick your fingers in and lift them a little)
On the Stromberg sectional drawings it clearly shows the passage way from the manifold side of the carb to the dashpot. The reason why they are called Constant Depression carburettors.

Interesting reading on the CD carbs.
P.S. they do not work like S.U. carbs, almost but not quite.

[David]

Re: Triumph twin Strombergs...

As a casual observer, it looks to me as if carbs and manifold are mismatched. I cant see how the dashpot can lift when there is no drillings in the manifold to facilitate this.
All the carb faces suggest there should be a way of the depression in the manifold lifting the dashpot also the carb mounting plate shows holes to match the carbs but the manifold does not. The fact that you have run the engine on easy start administered through the air intake confirms that no fuel is getting past the carbs, as would be the case if the dashpots were unable to lift.
Is there a way you could lift the dashpots manually when you start the engine, in a way of mimicking the manifold depression lifting the Dashpots, its worth a try.

Is it possible the manifold was for S U carbs and not Strombergs

Good points, which is why I took a look at the old carbs, and whilst these to have a couple of holes on the manifold side of the castings both were blocked by the old gaskets, and as I said there are no corresponding holes in the manifold anyway. The car ran fine with the old carbs. Top picture above.

Maybe there's something on the old carbs that I'm missing on the new, superficially they look the same bar the inlets for the rocker box cover breather but internally they were different in the float chamber with a pipe next to the jet, so who knows what other differences they have!

I'm just hoping the supplier will know what's going on as these new items were supplied as 'direct replacements' for the old carbs.

Details on operation of the CD type carb here