Triumph twin Strombergs...

[David]

Re: Triumph twin Strombergs...

Double checked timing, it's not 180 out (was running prior to carb replacement), I will check the spark again today but as I say this is all new kit (disci, leads, plugs, coil etc) that was running fine.

Checked the gaskets and in fact left the air filters off to be sure. I don't think there's a port on the carb to manifold side is there? I vaguely recall seeing a type of gasket for that location with a circular cut out on the ID edge, was that on very late cars, no port to match on the inlet anyway (worth me looking at today!)

Can't fit the old carbs now as I had to cannibalise one for good a part to replace a faulty part on the 'new' carbs.

Andy: No, no great smell of fuel but plugs are wet and smell of fuel. No attempt to fire at all.

So, this afternoon a few things to look at.

[David]

Re: Triumph twin Strombergs...

Back from Halfords, Easy Start in hand and it runs, https://youtu.be/VAtwVuDAKw8.

I checked the old carbs and they do have two holes on the inlet side of the casting but these were covered by gasket, see attached photo.

The 'new' carbs appear to have just one hole (I only checked one carb) and these are also covered with the new gasket and there's no matching hole on the manifold. It would make sense that if these holes were expecting to line up with holes in the manifold for some sort of vacuum or pressure to enable operation then that maybe the problem. But I'm out of knowledge now so will have to call the firm that built them tomorrow.

Final photo of the holes in the front of the carbs and that they are NOT covered up by the front plate, which has corresponding holes.

That's it for the day, I have to attend to the household list now to keep the brownie points topped up

[philcoyle]

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

[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

[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.

[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.

[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...

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...

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

[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...

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...

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.

[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.

[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....

[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?