Triumph twin Strombergs...

[David]

Here's a Sunday night topic to keep you awake.

My Marlin has a MK2 Vitesse engine, according to the serial number. As purchased it had 'Emission Control' carbs on it and the build photo's from the mid 80's appear to confirm they've been on there since then. The setup will be familiar to Vitesse and early GT6 owners of a breather pipe from the rocker box to a breather valve and then into the inlet manifold. All good so far. Mine has a brake servo so there's a T on the manifold to take vacuum off to the servo. See photo.

Today I started the job of replacing the carbs and appear to have ended up with (GT6 MK3) carbs which have the vacuum connectors on the manifold side of the bodies and some of you may know that at this time Triumph did away with the breather valve, T'd these two connectors to a single hose onto the rocker breather.

So my question is should I:

a) Just blank the vacuum pipes on the carbs, or connect them? (simplest option, mimicking the old 'Vitesse' setup)
b) connect them up to the breather valve and remove the T on the manifold leaving a single vacuum connector for the servo (non standard?)
c) bin the breather valve, and connect the carbs vacuum outlets via a T to the crankcase pipe? (GT6 MK3 style)

I suspect any and all of the above will work, I have no idea if my engine has the later emissions control disti or cam etc

Photo's attached showing the old setup, new vs old carbs with vacuum connectors highlighted.

thanks, David.

[d mulcahy]

Re: Triumph twin Strombergs...

I have a Triumph engined roadster and have replaced all rubber hoses, when replacing the hoses connected to the valve mentioned I noticed the hose inner diameter was a lot smaller to increase pressure to the valve. When I asked Rimmers if the replacement was the same as the original and informed that it was of one diameter and did not matter but why then would Triumph make a specific hose to do a certain job beats me.

[d mulcahy]

Re: Triumph twin Strombergs...

P.S. may be selling due to I'll health so the problem will not be a problem soon, unfortunately.

[David]

Re: Triumph twin Strombergs...

Here's a thought, prompted by Dave's mention of pressure.

The early setup relied on pressure to pop the breather valve to vent fumes back into the inlet manifold.

The later setup presumably creates a vacuum caused by the airflow through the carbs which will pull fumes out of the engine.

So maybe the question should be is the MK2 Vitesse engine happier under pressure or vacuum. Does the latter setup just create linear neutral effect whereas the old style breather valve would allow pressure to build and then release in a an on off fashion.

More Google searching for original documentation I suspect... but I'll probably end up with setup C) as per this photo but with a manful take off for the brake servo vacuum line.

Edit: Eighth post down this page seems to be useful
http://club.triumph.org.uk/cgi-bin/f...5719993/s-all/

David,

[David]

Re: Triumph twin Strombergs...

Decision.

I'm going for option C (bin the breather valve, and connect the carbs vacuum outlets via a T to the crankcase pipe) for the following reasons;

- The carbs have been designed to do the breather recirculating job
- Presumably this is a 'better' solution as Triumph adopted it on later cars (GT6's)
- I can remove the breather valve reducing the number of things needed to maintain.

Rimmer Bros do the pipe's and T pieces needed as well as a single outlet inlet fitting for the brake servo vacuum pipe.

David.

[hkp57]

Re: Triumph twin Strombergs...

I agree with your selection of option three, in chronological sequence this was the route the manufactures went last so presume the best.

Main benefit to you is the PSV needs maintenance and going through the carbs does not. Same in reality to my breather question on the B series engine.

The thoughts above about the PSV giving you an on off breather system is not correct, they function to give you a low constant vacuum on the crankcase and is what you need.

http://mgaguru.com/mgtech/engine/cv103.htm

[stevejgreen]

Re: Triumph twin Strombergs...

Can't see why a smaller internal diameter hose should impact air pressure unless there is a very significant flow.

[David]

Re: Triumph twin Strombergs...

I agree with your selection of option three, in chronological sequence this was the route the manufactures went last so presume the best.

Main benefit to you is the PSV needs maintenance and going through the carbs does not. Same in reality to my breather question on the B series engine.

The thoughts above about the PSV giving you an on off breather system is not correct, they function to give you a low constant vacuum on the crankcase and is what you need.

http://mgaguru.com/mgtech/engine/cv103.htm

Thanks for that, an interesting read.

[David]

Re: Triumph twin Strombergs...

Next episode...

So carbs are on and whilst removing the early model Vitesse/GT6 breather assembly I also removed the T piece from the centre of the inlet manifold. One side of the T returned the crankcase fumes to the inlet the other was a take off for the brake servo.

It gets interesting here. The vacuum pipe is actually connected via a reducer to the other side of the T piece, I hadn't noticed this earlier. The replacement connector supplied by Rimmers is too large a bore for the vacuum pipe. Not surprising as the Rimmer piece supplied is probably for the larger bore fume return pipe so I'll just use the old reducer screwed directly into the manifold.

As an aside this T and reducer look suspiciously like domestic plumbing parts!

On looking at the reducer it has something inside, is this some soft of filter to prevent fuel getting to the brake servo, or is it something else, a one way valve perhaps? My question being should any inlet manifold vacuum take off for a brake zero be 'filtered', makes sense not to send fuel/air mix to the servo after all.

Photo's attached as usual. Hope you're all having as nice weather as we are here.

[greyV8pete]

Re: Triumph twin Strombergs...

A chap that supplied me with some brake servo parts a while ago used to work for Girling (when they actually made things in the UK!) and told me that with "old style" carb engines which are quite generous with the amount of petrol they spread around, you should have a U-trap (approx 200mm deep) in the vacuum line. This can be 8mm bundy or copper pipe and can be fitted on the inner wing, preferably somewhere that it can get warm. Any fuel that gets into the line will then evaporate preventing any liquid fuel getting to the servo diaphragm. Peter.

[David]

Re: Triumph twin Strombergs...

Thanks Peter that's a useful tip and I have some copper pipe laying around so will see how that could work.

Also, petrol U trap and non return valve's mentioned in this Delphi PDF. It does appear that some (later?) servos have a non return valve incorporated within the unit.

http://www.mossmotors.com/graphics/p...DF/981-173.pdf

So, another update, isn't the Internet wondeful. Seems that the 'reducer' I'm talking about is in fact the non return valve mentioned in the above PDF. Carried by Rimmers;

http://www.rimmerbros.co.uk/Item--i-ADU1402

So I'm all set bar dropping a U bend into the line as per Pete's note and the Delphi document. I have however noted that the servo is supposed to be installed at between 25-45 degree incline whereas mine is mounted on the horizontal.

[greyV8pete]

Re: Triumph twin Strombergs...

I seem to remember that the front of the servo being higher is to facilitate bleeding the hydraulics. Peter.

[David]

Re: Triumph twin Strombergs...

I seem to remember that the front of the servo being higher is to facilitate bleeding the hydraulics. Peter.

That makes sense. Next time I need to bleed them I'll re-mount the servo!

David.
Wishing I did all this over the winter...

[djj_engineer]

Re: Triumph twin Strombergs...

Tolkien has a rocker box breather valve and wont run properly without it. I had the carbs rebuilt by Burlen Services ( SU carb builders)
The brakes don't have a servo. Doug removed it during his ownership but it doesn't seem to have had much load difference to the foot-brake so I left well alone when i rebuilt the system.
The main problem I found was a thorn shaped needle of solder in the fuel line to the front carb. It seemed to be interfering with the float needle on that carb making setting the carb for mixture very difficult!

[David]

Re: Triumph twin Strombergs...

Well a good weekends work and everything is back together;

- Refurbished carbs, with breather inlets fitted
- Smiths style early breather valve gone
- Crankcase breather routed to carbs
- Non return valve refitted and plumbed to a new U bend onwards to the brake servo
- All new plumbing...

So, filled the dashpots, turned the key waited to hear fuel going into the carbs. OK I can hear that, but hang on I can also hear fuel pouring onto the floor.

I thought it would be simple pipe clip tighten but alas no, fuel is pouring out of the front (air filter side) of the rear carb. Front carb is fine.

So, what's going on. Any ideas?

Over pressure, causing nearest carb to the pump to leak? I don't think I have a regulator. Perhaps I should install one. But nothings changed on the pump side, still the same electric pump.

Annoyingly the reason I swapped the carbs, apart from being very worn, was that on the old set the rear leaked occasionally, silly me was thinking it was a jamming float chamber valve but perhaps that was a mis diagnosis!