Genuine help from you experts needed!!

[Forkie]

Ok so i'm not ignoring the last few messages between us but i am trying to stay focused on where i am right now with the tests on the carbs as planned, and i simply don't have the spare time to be on it daily so there will always be short breaks in between.
Here is my latest results - which i do find even more interesting ! So now bear in mind the piston assemblies are now swapped , so front assembly in rear, rear in front. Everything else is as was. Last night removed FRONT piston assembly ( which was the rear) , sat it upside down into a jar to drain the oil. 24 hours later - this eve - clean oil in jar from said piston. Ideal. Used meths on inside of front dashpot and outside of piston- they were clean but just a belt and brace job. Oil that drained out was perfect . Had a torch, magnifying glass AND my glasses to check jet and needle - to me, jet is circular, not oval, and no signs of scoring to needle, although as i believe was mention it seems 'sprung ' off center.

[Forkie]

So now oil is drained from dashpot i can do the ' drop' test. This is where i need advice on if im doing it correctly. I am getting mixed info on certain aspects so it was done in two ways. So im holding the assemblies, my lad is on the stopwatch . Each test was done 4 times, to get an average. First test - dashpot upside down, no damper fitted, piston inserted, hold base of piston and let the dashpot drop down - at the point of seperation with a 'pop' - average 4 seconds. Second test, in exactly the same manner but with damper now fitted - average 3 seconds. Both large holes in piston base plugged on both tests with blue tac. According to the 'old google' - the Haynes - thats a fail. Answers on a postcard please !!!

[Alec]

Hello Forkie,

that both have identical times sounds good, that means the pistons should rise and fall in unison which is what you want.

Alec

[Alec]

Hello Forkie,

I just checked mu S.U. manual and the way they test them is with the damper in, blocking the holes and with a small nut and bolt with a large washer which acts as a stop to prevent the damper leaving the piston. Their time is 5 to 7 seconds from fully in to hitting the washer at the base of the damper.
Your 3 seconds seems to indicate that there is too much gap between piston and damper.
I would suggest a call to Burlen Services technical department would be useful?

Alec

[Forkie]

Yes thats what i read in the Haynes, 5 - 7 seconds, so a fail. I did not use the screw etc, could not see how that is really relevant, i just had my hand directly underneath ready to catch the falling dashpot.
So this eve will be a repeat to the rear dashpot ( now with front piston) and see what that gives me. Then i will swap the pistons back to where they were, and test both all over again. Will put up the results.
Regarding Burlens - i have already looked at their site, and worryingly HS6 complete Carb replacements are N/A. Whether that is permanent, or temporary at this point i am not sure.

[Forkie]

Ok so here we go - so this is the rear carb, but with front piston - the oil in the damper was clean, but way darker than the rear one,not sure of the significance of that. Everything else ditto - i.e. no scoring to needle, needle slightly sprung off center, jet looks ok, no obvious ovality.
Drop test - as per front one x 4 or more !! - without damper fitted - just below 5. WITH damper fitted - around 5.
So now, pistons reversed, back to how they were - readings now all with damper IN - FRONT - between 4.9 / 5.5 ( this being suspected weak running carb). REAR - barely 4.00 , and several tests ( this being suspected corectly running carb). So all in all, ALL these tests indicate both are on the lower end, or lower than the reccommended time.
The big question - would this indicate the reason for my lack of power/ no top end acceleration?

[Alec]

Hello Forkie,

I mistakenly thought that you had tested both together.

You do not need a new carburettor, but possubly new dashpot and piston assembly. If the seal is below specification i.e. falling too fast, this will slow the rate of lift when you accelerate so richening the mixture, and if pistons are not matched then this will affect some cylinders more than the others. (Quite what the effect of the balance pipe has on mixture distribution between cylinders I can't begin to guess?)
That is why I suggested talking to Burlen as they may be able to offer a practical solution, e.g., spring rate has a bearing on the rate of rise of the piston.
Incidentally many years ago when doing a comprehensive rebuild to a car I ordered, over the phone, a set of piston dashpot assemblies and the Burlen representitive queried why I wanted them as they very rarely wear, basically as there is no contact between piston skirt and dashpot outer.
It is likely that yours have had an abrasive clean in the past and that is why the drop test is on the low side?

Alec

[Forkie]

Not sure, the one thing that the test DOES NOT mention is as well as plugging the by- pass holes in the piston base - no mention of plugging the tiny breather hole int the damper cap....we did just that, and it slows the fall down considerably .....
Well i woke up at 2 am this morn with a light bulb flashing before my eyes ... i am obviously well aware of the need for the oil in the dashpots, and from past memory of cars that have not been checked or topped up it can cause all manner of running issues, hesitation etc. But how crucial is tha actual level in the tubes, i know the book gives a level which looks like the top of the tube. What im trying to say is if they were too low a level, would the engine start up and run ok at low speed, but start struggling the faster you try to go....

[Alec]

Hello Forkie,

I don't know why S.U. say to test with the damper in place, it only works with the piston rising, not falling. Blocking that breather hole will not give an accurate test I don't think.

All the oil level needs to do is cover the damper base as a minimum, as the piston rises the oil level relative to the damper sleeve increases.. If you fill it right up, it will be ejected through the breather hole when the throttle is fairly wide open.

Alec

[Forkie]

Mmm ok. I've got another set of eyes and ears coming round tommorrow to have a look over it, a friend of mine has suggested him as he is a bit more of an ' old school' mechanic and works on the older stuff so will see what he finds.