Genuine help from you experts needed!!

[Forkie]

Part 3. By the way, all this is being done on a cold, non running engine. Foot to the floor on accelerator brings the stop clamps right round to their stops, butterfly valves to rear of carb bodies fully open.
Choke setting - there is at least 20mm of choke pull inside the car before anything moves at the linkages - so that is obviously not right. Accelerator cable does also have a tad of pick up before any movement, but not as much as the choke set up.
Await replies but i am wondering if i have had too much faith in the p.o. for it being set up correct - i am starting to wonder if he has not put the carbs back in the right order at some point, i have always assumed he had....is that my issue? The carbs just felt better when i swapped the pistons over.....i have read somewhere to be carefull interchanging as the dashpots/piston assembly are machine matched to fit..
Any input would be appreciated.

[johnnydog]

Interesting results...
Is the jet visibly round or oval on either carb? If not, I'd continue with Pt 2. Changing the piston and needle as complete assemblies is easy to return to the original if necessary.
If they are oval, then the needle and jet need replacing anyway.
I appreciate that keeping the piston in its respective carb is probably recommended, but I have played around with HS6's over the years, and not found changing pistons only (from a different set if carbs) has had any detrimental effect. From your experiments, I still think that maybe the needle in the affected carb is slightly bent out of true, rather than the fault being with the piston itself or the spring.

[Forkie]

Hi John,
Yes i found the results interesting too. Simply swapping the springs, which then cancelled out the stutter was the most baffelling!!!! Interesting that you say you have inserted different piston assemblies into dashpots before with no adverse effect - so i feel happier at that to try it that way for now. I mean , if now i am thinking the p.o. DID at some point muddle them up, it's now been running for ? years/miles in a 'non matched pairing ' anyway!! Neither dashpot internal face or piston outer face shows any sign of scoring or anything else so im happy with that.
Regarding ovality of jets - as far as i have noticed so far they both look good to me. Todays examination/tests were going to be a further/closer look at the jet holes, to empty the oil from the piston rods and clean with meths, which then affords me a proper look at the inverted needles etc, and to do the upside down drop test of piston into dashpot. Sadly for me i had to change plans again as the daughter's car needed help so that was that i will get those tests done during this week.
As a p.s. - what oil do you find best for the dashpots - ive only ever used engine oil, i am getting conflicting views even on that....

[johnnydog]

There are different schools of thought on the oil for the piston damper - the handbook states 20 /50, other say a thinner viscosity.
I personally, I use a 10/40 (I use that in my other 'non Triumph' cars), which is slightly thinner, especially when cold.
Being perfectly honest though, I've not noticied any difference when using either of those oil viscosities in the carbs.

Incidentally, did you check the float valve in the top of the float bowls - especially the problematic one? When Dave B and myself were diagnosing a stutter and and its refusal to rev on his 2500 with HS6's, the lack of power even at low revs was found to be one of the float valves was faulty and not letting sufficient fuel into the bowl. It wasn't stuck, it just wasn't letting enough fuel through. A change of float tops cured it (bearing in mind there are different types of float).

[Forkie]

Ok so using the 20/50 that is in them now is not really the incorrect grade!!!! I am not alone then, that there are many differing views.
Re float valve - i get your suggestion - and hands up i have not even removed either float lid as yet ( they have been off in my ownership, cleaned out and new gaskets) - the reason being is that even though i appeared to have that stuttering front dashpot, it WASN'T being noticed in start up, or pull away - it starts absolutely fine, and pulls away in the expected smooth manner,without any hesitation at all. That is the main reason i was surprised when i noticed that stutter - it wasnt being noticed in start up or initial pull away....
Are you suggesting, bearing in mind the above, that my bigger issue - no top end speed/ lack of overall power, might well be a dodgy float?
* even though it does not show in initial start up / pull away. I would of thought any sticking or stuttering would show up more from the off/ cold.

[Alec]

Hello Forkie,

there is a specific S.u. oil which, from memory is a straight 20 grade but when I had S.U.'s I always used engine (20/50) oil.

Alec

[Forkie]

Hi Alec,
Yes , the brother in law was talked into purchasing proper SU oil, for the carbs, for his Sprint. But i have always only ever used the same 20/50 oil as per the engine grade, without any adverse issue.So with John and yourself both agreeing on 20/50 i am happy with the fact the oil i have been using should be fine. It seemed fine decades ago with my Minis' ,Allegros etc so why would it be different now!! I appreciate the continued interest.

Regards, Nige.

[Forkie]

John ,
So if it wasnt stuck, what was the reason for not letting enough fuel through? But like i have mentioned, mine is not stuttering or hesitating at all, at start up or low speed anyways !! It is after 35 40 mph the problem starts - could that still be float related ?

[Alec]

Hello Nige,

there is an old practice used in motor racing of what was called 'Plug cutting' to gauge mixture strength, pre days of sophisticated mixture analysis.

It was used to check full power setting but the same can be done with your car when it reaches the stuttering stage. A suitable relativly traffic free road is required, run the car until it stutters n(ideally for as long as posible), de clutch and simultaneously switch the ignition off. Then remove the plugs and see what colour they are. Probably the hardest is finding a suitable bit of road where you can carry out the test and coast to a layby to check the plugs?

Alec

[johnnydog]

We checked them by trying to blow through the fuel inlet pipe, and operating the float, to see if they shut off correctly, as fuel delivery / starvation was suspected as it wouldn't rev. There was a problem with one float valve - I think from memory, it wasn't allowing sufficient fuel through, rather than not shutting off, which affected the fuel delivery into that particular bowl. A used one off another carb cured it.
Not much help, I guess, but I only suggested it as another easy item to check!